《材料表面与界面》课程教学资源（文献资料）二氧化碳在多孔材料上的吸附 Sub-Angstrom Level for Maximizing Specific Capacitance and CO2 Uptake

Makrials Vies 器 www.MaterialsViews.com www.afm-joumal.de A New Approach to Tuning Carbon Ultramicropore Size at Sub-Angstrom Level for Maximizing Specific Capacitance FULL and CO2 Uptake PAPER Jin Zhou,Zhaohui Li,Wei Xing,*Honglong Shen,Xu Bi,Tingting Zhu,Zhipeng Qiu, and Shuping Zhuo* was obtained when the pore size of carbon Ultramicroporous carbon materials with uniform pore size accurately materials matched the dimensions of adjusted to the dimension of electrolyte ions or CO2 molecule are highly the electrolyte ion.With regard to CO, applications.it has been widely efficient ways to fine-tuning ultramicropore size at angstrom level are scarce. A completely new approach to precisely tuning carbon ultramicropore size at Cothe ome sub-angstrom level is proposed herein.Due to the varying activating strength 。 and size of the alkali ions,the ultramicropore size can be finely tuned in the range of 0.60-0.76 nm as the activation ion varies from Litto Cs*.The car. bons prepared by direct pyrolysis of alkali salts of carboxylic phenolic resins yield ultrahigh capacitances of up to 223 Fg-(205 Fcm in ionic liquid diame Puher electrolyte,and superior CO2 uptake of 5.20 mmol g-1 at 1.0 bar and 25 C. studies showed that CO2 uptake is lim- ited by ultramicropores smaller than a Such outstanding performance of the finely tuned carbons lies in its adjust certain diameter at different pressures or able pore size perfectly adapted to the electrolyte ions and CO2 molecule.This temperatures.On the other hand,the work paves the way for a new route to finely tuning ultramicropore size at the volumetric performance is of great impor sub-angstrom level in carbon materials. tance for practical application of carbon materials in supercap citors and co,cap ture.In this sense,high packing density of 1.Introduction 、Crbon mera eh机ati ecent s for materials. with capacitance and CO uptak carbon r electrolyte ions or the CO2 molecule may result in materials diameter smaller than 1.0 nm to be responsible for an anom- exhibiting optimal performance.These impressively show the alous increase in specific capacitance in organic electrolyte importance of uniformly adjusting the ultramicropore size at media.It is suggested that desolvated ions rather than larger- sized solvated ionic species are stored in these ultramicropores. cphyim地me me In the case of ionic liquid (IL)media,maximum capacitance and polymer carbonizationl13 allow production of porous carbon materials with developed porosity.These methods,how- ever,typically lead to poor fine tuning of ultramicropore size hou,H.Shen, 马 at sub-angstrom levels.The most successful synthesis strate gies to control micropore size are based on the selective deal. oving of metal carbides by chlorination.although chlorine gas E-mail:zhuosp_academic@yahoo.com from 0.7t01.0n of ust sofu of He 照 energy-cor suming t tures proces ously hinder large-scaleonmufcnword,efficient ways to precise fine-tuning the ultramicropore size of carbons D010.1002/adfm.201601904 are scarce.It is still very challenging to develop facile approach 0L10o0290010 2016 WILEY-VCH Verlag GmbH Co.KGaA.Weinheim wileyonlinelibrary.com 1

full paper © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 1 was obtained when the pore size of carbon materials matched the dimensions of the electrolyte ion.[4] With regard to CO2 capture applications, it has been widely accepted that CO2 uptake at ambient pressure is determined by the volume of ultramicropores rather than the total pore volume.[5,6] Presser et al. reported that most of the CO2 uptake capacity of carbide derived carbons at ambient pres￾sure to be originated by pores with a diameter smaller than 0.8 nm.[7] Further studies showed that CO2 uptake is lim￾ited by ultramicropores smaller than a certain diameter at different pressures or temperatures.[7,8] On the other hand, the volumetric performance is of great impor￾tance for practical application of carbon materials in supercapacitors and CO2 cap￾ture. In this sense, high packing density of the carbon materials is preferred. As large pore size and broad pore size distribution are usually in contra￾diction with high packing density, uniform ultramicroporosity are highly desirable for maximizing volumetric capacitance and CO2 uptake for carbon materials. As pointed out above, carbons with uniform and fine tai￾lored ultramicropore size matching the dimensions of the electrolyte ions or the CO2 molecule may result in materials exhibiting optimal performance. These impressively show the importance of uniformly adjusting the ultramicropore size at sub-angstrom levels. Well-established methods such as chem￾ical activation,[9,10] physical activation,[11] template methods,[12] and polymer carbonization[13] allow production of porous carbon materials with developed porosity. These methods, how￾ever, typically lead to poor fine tuning of ultramicropore size at sub-angstrom levels. The most successful synthesis strate￾gies to control micropore size are based on the selective deal￾loying of metal carbides by chlorination, although chlorine gas is very toxic.[14] Hou et al. reported a hot-pressing method to adjust the average pore size of zeolite-templated carbons from 0.7 to 1.0 nm at the expense of using ultrahigh pressures of up to 147 MPa.[15] Cyclic oxidation/thermal desorption treatment allows gradual adjustment of average pore size, although the time- and energy-consuming features of this process seriously hinder large-scale carbon manufacturing.[16] In a word, efficient ways to precise fine-tuning the ultramicropore size of carbons are scarce. It is still very challenging to develop facile approach A New Approach to Tuning Carbon Ultramicropore Size at Sub-Angstrom Level for Maximizing Specific Capacitance and CO2 Uptake Jin Zhou, Zhaohui Li, Wei Xing,* Honglong Shen, Xu Bi, Tingting Zhu, Zhipeng Qiu, and Shuping Zhuo* Ultramicroporous carbon materials with uniform pore size accurately adjusted to the dimension of electrolyte ions or CO2 molecule are highly desirable for maximizing specific capacitance and CO2 uptake. However, efficient ways to fine-tuning ultramicropore size at angstrom level are scarce. A completely new approach to precisely tuning carbon ultramicropore size at sub-angstrom level is proposed herein. Due to the varying activating strength and size of the alkali ions, the ultramicropore size can be finely tuned in the range of 0.60–0.76 nm as the activation ion varies from Li+ to Cs+. The car￾bons prepared by direct pyrolysis of alkali salts of carboxylic phenolic resins yield ultrahigh capacitances of up to 223 F g-1 (205 F cm-3 ) in ionic liquid electrolyte, and superior CO2 uptake of 5.20 mmol g-1 at 1.0 bar and 25 °C. Such outstanding performance of the finely tuned carbons lies in its adjust￾able pore size perfectly adapted to the electrolyte ions and CO2 molecule. This work paves the way for a new route to finely tuning ultramicropore size at the sub-angstrom level in carbon materials. DOI: 10.1002/adfm.201601904 Dr. J. Zhou, Z. Li, H. Shen, X. Bi, T. Zhu, Z. Qiu, Prof. S. Zhuo School of Chemical Engineering Shandong University of Technology Zibo 255049, P. R. China E-mail: zhuosp_academic@yahoo.com Prof. W. Xing School of Science State Key Laboratory of Heavy Oil Processing China University of Petroleum Qingdao 266580, P. R. China E-mail: xingwei@upc.edu.cn 1. Introduction Carbon materials have received considerable attention in super￾capacitors and CO2 capture.[1] Recent studies have shown that ultramicropores (diameter <0.80 nm) play a key role in deter￾mining specific capacitance and CO2 uptake of carbon mate￾rials.[2–8] Chmiola et al. pointed out that micropores with a diameter smaller than 1.0 nm to be responsible for an anom￾alous increase in specific capacitance in organic electrolyte media.[3] It is suggested that desolvated ions rather than larger￾sized solvated ionic species are stored in these ultramicropores. In the case of ionic liquid (IL) media, maximum capacitance Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201601904 www.afm-journal.de www.MaterialsViews.com

5器 Makials www.afm-journal.de Vieus www.MaterialsViews.com to tuning carbon ultramicropore size at sub-angstrom level the nucleophilic addition reaction between phenols and for- when keeping the pore uniformity. maldehyde leads to the formation of hydroxymethyl derivatives Herein,we proposed a completely new strategy to finely that subsequently undergo intermolecular condensation (i.e., tune the pore size of ultramicroporous carbons using different dehydration)to yield methylene and methylene ether bridges. The formation of hydroxymethyl derivatives is very fast at the basic conditions used herein (pH =10).this resulting in a pared by direct carbonization of alkali peeDueoegg2ta large number of primary particles and thus small-sized res porting Information) ns,the ultramic of0.600.76 asheCea The high surface tensi g2actnces1 ng in com rolyte,and s up to 223 F e resulting ting of gel cm id e of 5.20 mmo ga10 (Figure S Supporting I by c and 25 C.To the best of knowledge,these value higher than most of the reported carbon materials.Theo tion at min-)for 2 h in argon.The alkali meta ion-activated carbon materials were finally obtained by washing standing performance of the finely tuned carbons was proved with diluted HCl and deionized water to neutrality.For conven- to lie in its pore size perfectly adjusted to dimensions of the ience,the alkali salts of carboxylic phenolic resin and its corre ions composing the ionic liquids and the CO2 molecule. sponding carbon material are denoted as PR-COOM and MAC, where PR and M stand for phenolic resin and alkali metal ion, respectively. 2.Results and Discussion As illustrated by X-ray energy dispersive spectroscopy (EDS) mapping (Figure S3,Supporting Information).the distribu- 2.1.Formation of the Ultramicroporous Carbon Materials tions of alkali ions are homogeneous.These monodispersed ions as a form of-COOM could produce a homogeneous"in Figure 1 illistrates the preparation of the ultramicroporous situ activation"effect.To study the carbonization process and naterials In a yn 2 4.dibud. acid.alkali hydroxide (MOH). dis. TG-MS)a alysis and in situ x o(XRD)were per med 2a-d sho the TG c nd MS solution. of carboxylic (PR-COOK) between strongly carboxyl groups of 2.4-dihydroxybenzoic acid to form carboxylates ( 2boracaP This solution was then hydrothermally treated at 120 24 h to promote polymerization of phenols with formaldehyde at T<200C could be attributed to the evaporation of mois. resulting in alkali salts of carboxylic phenolic resins.Initially, ture and decarboxylation confirmed by the release of H2o Hydrothermal Drying xeroge M+=Lit,Na',K',Rb*,Cs* Carbonization 250 0.8 ±200 150 pore size of carbons 0 100 2 0.2 activation ion size 0.0 Li Na K Rb Cs 08i Li Na K Rb Cs MAC Figure 1.Sche of the nthesis of MAC. 2016 WILEY-VCH Verlag GmbH Co.KGaA.Weinheim Ady Funct.Mater.2016 D0t10.1002/adfm.201601904

full paper 2 wileyonlinelibrary.com © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim to tuning carbon ultramicropore size at sub-angstrom level when keeping the pore uniformity. Herein, we proposed a completely new strategy to finely tune the pore size of ultramicroporous carbons using different alkali metal ions (Li+, Na+, K+, Rb+, Cs+) as activating agents. Ultramicroporous carbons with highly uniform pores and high packing density were prepared by direct carbonization of alkali salts of carboxylic phenolic resins. Due to the varying activating strength and size of alkali ions, the ultramicropore size can be finely tuned in the range of 0.60–0.76 nm as the activation ion varies from Li+ to Cs+. The resulting carbons present ultrahigh capacitances of up to 223 F g−1 or 205 F cm−3 in ionic liquid electrolyte, and superior CO2 uptake of 5.20 mmol g−1 at 1.0 bar and 25 °C. To the best of knowledge, these values are much higher than most of the reported carbon materials. The out￾standing performance of the finely tuned carbons was proved to lie in its pore size perfectly adjusted to dimensions of the ions composing the ionic liquids and the CO2 molecule. 2. Results and Discussion 2.1. Formation of the Ultramicroporous Carbon Materials Figure 1 illustrates the preparation of the ultramicroporous carbon materials. In a typical synthesis, 2,4-dihydroxybenzoic acid, alkali hydroxide (MOH), and formaldehyde were dis￾solved in deionized water to form a pale yellow homogeneous solution. Immediately, a complete neutral reaction will occur between strongly basic MOH and carboxyl groups (COOH) of 2,4-dihydroxybenzoic acid to form carboxylates (COOM). This solution was then hydrothermally treated at 120 °C for 24 h to promote polymerization of phenols with formaldehyde resulting in alkali salts of carboxylic phenolic resins. Initially, the nucleophilic addition reaction between phenols and for￾maldehyde leads to the formation of hydroxymethyl derivatives that subsequently undergo intermolecular condensation (i.e., dehydration) to yield methylene and methylene ether bridges. The formation of hydroxymethyl derivatives is very fast at the basic conditions used herein (pH ≈10), this resulting in a large number of primary particles and thus small-sized resin gels (about 200 nm, Figure S1 (Supporting Information)).[17] The high surface tension generated during the hydrothermal process causes the packing texture of gel nanoparticles to col￾lapse, thereby resulting in compacting of gel particles.[18] The resulting red hydrogels were dried to form dark red xerogels (Figure S2, Supporting Information), followed by carboniza￾tion at 900 °C (3 °C min−1 ) for 2 h in argon. The alkali metal ion-activated carbon materials were finally obtained by washing with diluted HCl and deionized water to neutrality. For conven￾ience, the alkali salts of carboxylic phenolic resin and its corre￾sponding carbon material are denoted as PR-COOM and MAC, where PR and M stand for phenolic resin and alkali metal ion, respectively. As illustrated by X-ray energy dispersive spectroscopy (EDS) mapping (Figure S3, Supporting Information), the distribu￾tions of alkali ions are homogeneous. These monodispersed ions as a form of COOM could produce a homogeneous “in situ activation” effect. To study the carbonization process and activation mechanism, thermogravimetry-mass spectrometry (TG-MS) analysis and in situ X-ray diffraction (XRD) were per￾formed. Figure 2a–d shows the TG curves and MS responses of potassium salt of carboxylic phenolic resin (PR-COOK) and phenolic resin carboxylic acid (PR-COOH). Three gases, including H2O (m/z 18), CO (m/z 28), and CO2 (m/z 44), were detected by mass spectrometry. The little weight loss (<10 wt%) at T < 200 °C could be attributed to the evaporation of mois￾ture and decarboxylation confirmed by the release of H2O Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201601904 www.afm-journal.de www.MaterialsViews.com Figure 1. Schematic diagram of the synthesis of MAC

5器 www.MaterialsViews.con www.afm-journal.de (a) 6 (c) 100日 10 -PR-COOH 0 C0, 90 FULL PR-COO 20 -PR-COOH -PR-COOK 15 H 60 二pR8 PAPER 5 402004006008001000 2004006008001000 Temperature (C) Temperature (C) Ter ure(c) (d) (e) ⑧ Possible activation mechanism (1)PR-C00M-M2C03+C02+H20 800 (2)M2C03→M20+C0 orMC03+C-→M,O+2CO 000 (3)M20+C-M+C0 (4) 400 600 1000 and CO2(Figure 2a-c).In the case of PR-COOH,a significant which are attributed to K(100)(PDF card 01-0500)and KC weight1os of 38.3 wt%in 200-800C is due to th 100)(PDF t of Co w aoo of PR on t observed forme se t the porosi尚i黑hC二eR99 and parti is much more complicated at the temperatures above 200 calate between the carbon layers to form graphite intercalation- The weight loss of about 9.6 wt%in 200-400 C may be due like compounds (e.g.,KCs here)and cause swelling and the to further cross-linking and initial thermal degradation of the disruption of the carbon microstructure,which thereby gener phenolic resin with the formation of KCO,and evolution of ates even more ultramicroporosity.Similar results of TG-MS CO2 and H2O at about 350 C.The weight loss in 400-600 C analyses were obtained for the other alkali salts of carboxylic could be partially attributed to the transformation of K2CO phenolic resins (Figure S4.Supporting Information).indi. into K2O.The sharp weight loss (>20 wt%)above 800 C indi- cating the carbonization process is essentially same for all the cates that the carbon framework is severely etched to form the samples. microporosity. Overall.based on the above observations.a hom Figure 2e presents the in situ XRD patterns at 200.400. 600.and 800C during the olysis of PR-COOK.It can be into alkali car nate (M2CO).H2O.and CO,below 400C.Second.alkali (PDF card71-1466 at around200C.At600℃，the diffra oxides (M,O)are ition of of K2CO onger visible M.CO h nal decomc Third that st of K reaction ed b een transfo ormed K20. We igned a simple tion n of M 0m"s2M+ 20+0 experiment to prove the decomposition of K2CO3.As sho ight loss,t the produced metal es int in Figure S5 (Supporting Information).no precipitates the lattices of the carbon matrix,which is responsible for both were observed when the extract of carbonization residual of stabilization and widening of the interlayer spacing.The PR-COOK at 600C was dropped into BaCl2 solution,indi- interlayer spacing will be primarily determined by the size of cating the absence of CO32-in the residual.This further proves metal intercalate,and this spacing (i.e.,pore size)will be sys- that most K2CO,have been transformed into K2O at 600 C. tematically widened with increasing metal ion size from Lit to Considering the evolution of CO2 and CO at about 520C,the Cs+(Figure S6,Supporting Information).R1 After the removal generation of K2O could be explained by the possible reactions of the intercalated metallic alkali and other alkali compounds of K2C03→K0+Co2orK2C03+C→K0+2C0.When the by washing,the expanded carbon lattices cannot return to their carbonization temperature was increased up to 800C.besides revious nonporous structure and thus achieved to finely tun- the peaks of K,O.new peaks at 10.4 and 16.5 appeared, ble ultramicropore size. 2016 WILEY-VCH Verlag GmbH Co.KGaA,Weinheim

full paper © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 3 and CO2 (Figure 2a–c). In the case of PR-COOH, a significant weight loss of 38.3 wt% in 200–800 °C is due to the continual thermal decomposition of PR-COOH, and a negligible weight loss 20 wt%) above 800 °C indi￾cates that the carbon framework is severely etched to form the microporosity. Figure 2e presents the in situ XRD patterns at 200, 400, 600, and 800 °C during the pyrolysis of PR-COOK. It can be observed that the PR-COOK began to decompose into K2CO3 (PDF card 71-1466) at around 200 °C. At 600 °C, the diffrac￾tion peaks of K2CO3 are no longer visible and K2O (PDF card 26-1327) can be detected, indicating that most of K2CO3 has been transformed into K2O. We further designed a simple experiment to prove the decomposition of K2CO3. As shown in Figure S5 (Supporting Information), no precipitates were observed when the extract of carbonization residual of PR-COOK at 600 °C was dropped into BaCl2 solution, indi￾cating the absence of CO3 2− in the residual. This further proves that most K2CO3 have been transformed into K2O at 600 °C. Considering the evolution of CO2 and CO at about 520 °C, the generation of K2O could be explained by the possible reactions of K2CO3 → K2O + CO2 or K2CO3 + C → K2O + 2CO. When the carbonization temperature was increased up to 800 °C, besides the peaks of K2O, new peaks at 10.4° and 16.5° appeared, which are attributed to K (100) (PDF card 01-0500) and KC8 (100) (PDF card 04-0221), and large amount of CO were detected (Figure 2d). These facts indicate that K2O is reduced by carbon to metallic potassium via the reaction of K2O + C → 2K + CO, and partial carbon atoms were etched into CO to give rise to the porosity.[19] Meanwhile, potassium vapors may inter￾calate between the carbon layers to form graphite intercalation￾like compounds (e.g., KC8 here) and cause swelling and the disruption of the carbon microstructure, which thereby gener￾ates even more ultramicroporosity. Similar results of TG-MS analyses were obtained for the other alkali salts of carboxylic phenolic resins (Figure S4, Supporting Information), indi￾cating the carbonization process is essentially same for all the samples. Overall, based on the above observations, a homogeneous “in situ activation” process was presented in Figure 2f. That is: First, alkali salts of phenolic resins decompose into alkali car￾bonate (M2CO3), H2O, and CO2 below 400 °C. Second, alkali oxides (M2O) are generated via the thermal decomposition of M2CO3 or the redox reaction between M2CO3 and C. Third, framework carbon atoms are etched by M2O via the vigorous redox reaction of M2O + C → 2M + CO, leading to a significant weight loss, then the produced metallic alkali intercalates into the lattices of the carbon matrix, which is responsible for both stabilization and widening of the interlayer spacing.[20] The interlayer spacing will be primarily determined by the size of metal intercalate, and this spacing (i.e., pore size) will be sys￾tematically widened with increasing metal ion size from Li+ to Cs+ (Figure S6, Supporting Information).[21] After the removal of the intercalated metallic alkali and other alkali compounds by washing, the expanded carbon lattices cannot return to their previous nonporous structure and thus achieved to finely tun￾able ultramicropore size. Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201601904 www.afm-journal.de www.MaterialsViews.com Figure 2. a) TG curves, MS responses of evolved gases in TG-MS analysis b) H2O, c) CO2, and d) CO, e) in situ XRD patterns (Cu Ka) during the carbonization of PR-COOK, and f) possible activation mechanism

器 Maknials www.afm-journal.de ViewS www.MaterialsViews.com 200nm 200nm 5 nm g 5μm 200nm 200nm Figure 3.SEM images of a.b)KAC and e.f)CsAC.TEM images of:c.d)KAC and g.h)CsAC. other alkali metals)may be a reason.At 900C Li become leep of carbon Microscopic morphology and pore texture of MAC materials lattices,thus resulting in much more developed porosity.Even were imaged by scanning electron microscopy (SEM)and though the dosage of activation agents used herein was much transmission electron microscopy (TEM)techniques(Figure 3). lower compared to traditional chemical activation processes As revealed by SEM images,the MAC materials were shown (30 wt%of resins as counted in KOH vs 100-400 wt%).the sur- as compact blocks with a smooth surface and no clear pores. face area of KAC material (897 m2g-)was comparable to that However,when observed by TEM,the as-prepared carbons of KOH-activated carbons o2 were found to possess abundant micropores without apparent Dubinin-Radushkevich (D-R)plots from COz adsorption mesopore or macropore signs.High resolution TEM images data provide instructive information about the size of ultrami- ire S7 (Supporting Information)) cropores (diameter <0.8 nm).The slope from the linear D-R plots can be used to estimate micro ore size and uniformity within the MAC structures.These see the Su orting Information for further details).All the from the ho ation duce MAC rials ot liaC exhibited well-defined linear d-r elat 4c-f).In the MAC 1 near fitti ngs f high D-R plo two well-defi ed linear ard type I N2 adsorption a narrow knee at very low relative pressures(P/Po<0.02)and micropore systems(Figure S8,Supporting Information).Due nearly unchanged adsorption amount at higher relative pres- to the weak basicity of LiOH,the neutral reaction between sures.This shape is characteristic of porous materials showing 2,4-dihydroxybenzoic acid and LiOH is incomplete.The exist- a narrow micropore size distribution and a minimal presence ence of unreacted LiOH leads to an uneven dispersion of Lit of mesopores.As shown in Table 1,the SBer versus Smiero and in the phenolic resins,thus resulting in a wide pore size dis- V versus Vmicre values were very similar in all cases,further tribution of LiAC.Apparently.as the activation ions vary from demonstrating the microporous nature of MAC materials. Lit to Cst a systematic widening of micropores takes place Remarkably,the porosity of LiAC is much undeveloped,and the whose size gradually increases from 0.60 up to 0.76 nm.Thus. N,and CO,adsorption data.along with SEM and TEM obser- o-1 resnec vations revealed a purely uniform ultramicropore texture for MAC samples.Remarkably,the ultramicrop re size can be nd si level by the alkali m etal ior anged in react esins.The pared from ergies change( a 0 me red crystalline structure of MAC samples was at 900C with increasingly larger negative values (i.e.higher by XRD (Figure S9a,Supporting Information).XRD profiles reactivity of Mo and carbon)from Li to Cs.Furthermore,the typical of activated carbon materials were obtained with two difference of boiling points for alkali metals (1347 C for Li, broad bands centered at 23.4 and 43 corresponding to the 4 wileyonlinelibrary.com 2016 WILEY-VCH Verlag GmbH Co.KGaA,Weinheim

full paper 4 wileyonlinelibrary.com © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2.2. Structural Characteristics and Chemical Properties of MAC Materials Microscopic morphology and pore texture of MAC materials were imaged by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques (Figure 3). As revealed by SEM images, the MAC materials were shown as compact blocks with a smooth surface and no clear pores. However, when observed by TEM, the as-prepared carbons were found to possess abundant micropores without apparent mesopore or macropore signs. High resolution TEM images (Figure 3c,d,g,h and Figure S7 (Supporting Information)) clearly evidenced highly connected and worm-like micropores within the MAC structures. These pore morphology resulted from the homogeneous “in situ activation” produced by highly dispersed (at atomic level) alkali ions. The porosity properties of the MAC materials were further analyzed by N2 and CO2 adsorption at −196 and 0 °C, respec￾tively. As shown in Figure 4a, all the MAC samples except RbAC presented a standard type I N2 adsorption isotherm with a narrow knee at very low relative pressures (P/P0 0.995, Figure 4c–f). In the case of excellent linear fittings, Dubinin postulated the exist￾ence of highly uniform ultramicropores.[6,23] LiAC showed a D–R plot with two well-defined linear ranges, thereby indi￾cating the narrow microporosity to be composed of two micropore systems (Figure S8, Supporting Information). Due to the weak basicity of LiOH, the neutral reaction between 2,4-dihydroxybenzoic acid and LiOH is incomplete. The exist￾ence of unreacted LiOH leads to an uneven dispersion of Li+ in the phenolic resins, thus resulting in a wide pore size dis￾tribution of LiAC. Apparently, as the activation ions vary from Li+ to Cs+, a systematic widening of micropores takes place, whose size gradually increases from 0.60 up to 0.76 nm. Thus, N2 and CO2 adsorption data, along with SEM and TEM obser￾vations revealed a purely uniform ultramicropore texture for MAC samples. Remarkably, the ultramicropore size can be finely and simply adjusted at sub-angstrom level by varying the alkali metal ion exchanged in the parent carboxylic phe￾nolic resins. The pore size tuning resulted from the varying activating strength and ion sizes of the alkali metals from Li+ to Cs+. The crystalline structure of MAC samples was characterized by XRD (Figure S9a, Supporting Information). XRD profiles typical of activated carbon materials were obtained with two broad bands centered at 23.4° and 43° corresponding to the Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201601904 www.afm-journal.de www.MaterialsViews.com Figure 3. SEM images of: a,b) KAC and e,f) CsAC. TEM images of: c,d) KAC and g,h) CsAC

器 www.MaterialsViews.com www.afm-joumal.de (a) (b) a600 -LIAC FULL 500 NaAC- 128 400 10 KAC 300 000 PAPER 200 100 0 0.0 0.20.40.60.81.0 0.00 0.010.020.03 Relative Pressure(P/P) Relative Pressure(P/P (c) (d) 2.5 NaAC 2.0 KAC R=0.9960 R2=0.9995 2.0 L=0.63nm L=0.66nm 1.5 1.5 10 ■ 1.0 24681012 4681012 log'(P/P) log'(P/P) (e) () 2.5 RbAC ·CsAC 2.0 R2=0.9983 R=0.9984 L=0.75nm 2.0 L=0.76nm 10 12 log'(P/P) log'(P /P) Table 1.Textural properties of MAC samples. reflections of the (002)and (101)graphitic planes,respectively. The intensities of these bands decreased from Lit to Cs',in Na sorption COa sorption agreement with the higher activating strength of Cs+that leads to a carbonaceous structure with more defects Raman spectra Sample Img mg cm'em'g lcm'g Inm) (Figure S9b,Supporting Information)showed well-resolved G 111 0.07 0.05 0.0s 0.60/1.17 and D bands centered at 1589 and 1340 cm-.corres sponding NaAC 668 621 035 032 0.36 0.63 to the reflections of the ideal and the disordered graphitic lat- KAC 897 816 0.49 042 0.66 ice, 8)further aterials.X RbAC 1243 1073 0.70 0.55 0.51 0.75 CsAC 1312 1239 0.67 0.63 0.53 0.76 toeochemiclprop Only C and the (ure S1.Supererv rem species were detected size. and deionized water.The oxygen contents of MAC materials 2016 WILEY-VCH Verlag GmbH Co.KGaA.Weinheim wileyonlinelibrary.com 5

full paper © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 5 reflections of the (002) and (101) graphitic planes, respectively. The intensities of these bands decreased from Li+ to Cs+, in agreement with the higher activating strength of Cs+ that leads to a carbonaceous structure with more defects. Raman spectra (Figure S9b, Supporting Information) showed well-resolved G and D bands centered at 1589 and 1340 cm−1 , corresponding to the reflections of the ideal and the disordered graphitic lat￾tice, respectively. The low value of IG/ID (about 0.8) further revealed the amorphous nature of MAC materials. X-ray pho￾toelectron spectroscopy (XPS) measurements were conducted to determine the surface chemical properties of MAC mate￾rials (Figure S10, Supporting Information). Only C and O species were detected, thereby revealing complete removal of surface metal species by thorough washing with diluted HCl and deionized water. The oxygen contents of MAC materials Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201601904 www.afm-journal.de www.MaterialsViews.com Figure 4. a) Nitrogen adsorption isotherms. b) CO2 adsorption isotherms. Analysis of the narrow microporosity by Dubinin−Radushkevich equation of: c) NaAC, d) KAC, e) RbAC, and f) CsAC. Table 1. Textural properties of MAC samples. N2 sorption CO2 sorption Sample SBETa) [m2 g−1 ] Smicrob) [m2 g−1 ] VT c) [cm3 g−1 ] Vmicrod) [cm3 g−1 ] V0 e) [cm3 g−1 ] Lf) [nm] LiAC 111 93 0.07 0.05 0.05 0.60/1.17 NaAC 668 621 0.35 0.32 0.36 0.63 KAC 897 816 0.49 0.42 0.42 0.66 RbAC 1243 1073 0.70 0.55 0.51 0.75 CsAC 1312 1239 0.67 0.63 0.53 0.76 a)Brunauer–Emmett–Teller surface area; b)Micropore surface area calculated by the t-plot method; c)Total pore volume; d)Micropore volume calculated by the t-plot method; e)Micropore volume given by CO2 adsorption; f)Average micropore size

器 www.afm-journal.de www.MaterialsViews.com K b Cs)were determined to be 55. theeen that AC 2.3.Capacitive Performance of MAC Materials not cear exactly One possible reason is thedif s- others.The cau Capacitive performance of MAC materials was studied both rence in 6 M KOH and pure IL of 1-ethyl-3-methylimidazolium ala mmpChe a tetrafluoroborate (EMImBF)electrolytes (Figure 5).Nearly rectangular-like cyclic voltammetry (CV)curves,characteristic metals except Li become metallic vapor with high diffusivity. of double-layer capacitance,were obtained in all cases.To fur- and could easily contact with carbon surface and efficiently ther investigate the electrochemical performance of the MAC remove surface oxygen.This explains why surface oxygen con- materials,galvanostatic charge/discharge measurements were tent of LiAC is apparently higher than the others.High reso- carried out(Figure S12,Supporting Information).At 0.2 A g lution xPS was used to investigate the atom binding states of and in KOH,the specific capacitances were measured to be 43, the prepared carbons(Figure S11.Supporting Information).In 140,205,200.and 221 F g-i for LiAC.NaAC.KAC,RbAC.and the case of C-species.the peaks at 284.7.285.4.and 286.4 eV CsAC,respectively.At 0.2 A g-1 and in EMImBF.those were are assigned to sp2 hybridized carbon,carbon atoms single or 48,97,128.189,and 223 F g for LiAC,NaAC,KAC,RbAC, double bonded to oxygen,respectively.In the case of O-spe- and CsAC.respectively.The specific capacitance was plotted rsus disch ren density (Figures cd)Clearly CsAC red carb s,includi c-ooc show ved the hig 0 e peaks.3,and in the hih iitce0in ion (a) (b) -.-CsAC -LiAC 2 -NaAC 0.2 ·KaC- 0 0.0 -0.2 2 -·-RbAC -·CsAC 0. 0.9 -0.6 -0.3 0.0 0 0.51.01.5 20 Voltage(V) Voltage(V) (c) (d) 250 LiAC●NaAC 250 -LiAC 200 150 150 100 100 50 0 5 10 15 20 Current density (A g') Current density (Ag) (e) 1.0 0.20 (HOX 0.5 0.15 KOH 一KOH ●-EMImBF -EMImBF NaAC KAC RbAC CsAC 0.0 LiAC NaAC KAC RbAC CsAC Figure 5.Capacitive performance:a)CVcurves at 10mVs-in KOH electrolyte;b)CVcurves at 5 mV s-in EMImBF:c)specific capacitances in KOH electrolyte;and d)specific capacitance in EMImBF:e)areal capacitance at 0.2 Agf)capacitance ratio. 2016 WILEY-VCH Verlag GmbH Co.KGaA,Weinheim

full paper 6 wileyonlinelibrary.com © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (M = Li, Na, K, Rb, Cs) were determined to be 12.3, 5.5, 5.2, 6.1, and 8.2 at%, respectively. It could be seen that LiAC pos￾sesses much higher oxygen content than the others. The cause is not clear exactly. One possible reason is the difference of alkali metals in boiling point (1347 °C for Li, <900 °C for other alkali metals). At high temperatures (e.g., 900 °C), the alkali metals except Li become metallic vapor with high diffusivity, and could easily contact with carbon surface and efficiently remove surface oxygen. This explains why surface oxygen con￾tent of LiAC is apparently higher than the others. High reso￾lution XPS was used to investigate the atom binding states of the prepared carbons (Figure S11, Supporting Information). In the case of C-species, the peaks at 284.7, 285.4, and 286.4 eV are assigned to sp2 hybridized carbon, carbon atoms single or double bonded to oxygen, respectively. In the case of O-spe￾cies, three types of O-containing groups could be verified on the surface of the prepared carbons, including CO, OCO, and OCO, corresponding to the peaks at 531.2, 532.3, and 533.5 eV, respectively.[24] 2.3. Capacitive Performance of MAC Materials Capacitive performance of MAC materials was studied both in 6 m KOH and pure IL of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) electrolytes (Figure 5). Nearly rectangular-like cyclic voltammetry (CV) curves, characteristic of double-layer capacitance, were obtained in all cases. To fur￾ther investigate the electrochemical performance of the MAC materials, galvanostatic charge/discharge measurements were carried out (Figure S12, Supporting Information). At 0.2 A g−1 and in KOH, the specific capacitances were measured to be 43, 140, 205, 200, and 221 F g−1 for LiAC, NaAC, KAC, RbAC, and CsAC, respectively. At 0.2 A g−1 and in EMImBF4, those were 48, 97, 128, 189, and 223 F g−1 for LiAC, NaAC, KAC, RbAC, and CsAC, respectively. The specific capacitance was plotted versus discharge current density (Figures 5c,d). Clearly, CsAC showed the highest specific capacitance among the MAC sam￾ples in the entire range of current densities. CsAC showed ultrahigh specific capacitance (223 F g−1 ) at 0.2 A g−1 in ionic Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201601904 www.afm-journal.de www.MaterialsViews.com Figure 5. Capacitive performance: a) CV curves at 10 mV s−1 in KOH electrolyte; b) CV curves at 5 mV s−1 in EMImBF4; c) specific capacitances in KOH electrolyte; and d) specific capacitance in EMImBF4; e) areal capacitance at 0.2 A g−1 ; f) capacitance ratio

Makrials VieS 器 www.afm-joural.de www.MaterialsViews.com liquid electrolyte,and this value is one of the highest am 32.5 and 6.2 Wh kg for CsAC in IL and KOH electrolytes material ation) FULL r superca pacitor applications (especially in portable electronic devices) Supporting Information).Remarkably,the specific capacitance the specific volur netric capacitance is a more reliable parameter of the electrode was maintained at =191 F g(nearly 100% as compared to the gravimetric one.CsAC (packing density of capacitance retention),even after 10 000 cycles. 02moHsrsof PAPER The ultrahigh capacitance properties can be better under- 2.4.CO2 Sorption Performance of MAC Materials stood by studying the relationship between pore and ion size. Results of the areal capacitance and retention ratio as a func. CO2 capture has attracted considerable attention in recent e地a2a品 use of thamgemeeom haat 物 MAC.we carried out co.adsorption measurements at 10 and 20 bar (Figure 6).As reported in Table S3(Supporting Infor ntly lower values obtained for the rest of carbon materials.In mation).CsAC showed ry high CO uptake at 1 bar acitanc :in EMImBF 0 pore ndi. Capa re s nm) metal Grnd covale。ra hat are AC results can Figure 6c shows the CO adsorption isother erms of explained in terms of pore size and electrolyte ion size(EMIm' the MAC materials at 25C and 0-20 bar.RbAC exhibits the 0.76 nm,BF:0.45 nm,solvated K":0.31 nm,and solvated highest CO2 capacity,i.e.9.63 mmol g-(42.4 wt%)at 25 C OH-:0.35 nm).According to the equation of C=gA/d,the and 20 bar.The trend of CO2 uptakes at 20 bar is in good agree capacitance(C)ofa supercapacitor electrode mainly depends on ment with that of total pore volume.As shown in Table S5(Sup the electrode specific surface area (A).which must be as high as borting Information).the co,uptakes of CsAc are much less possible,and the distance (d)between the adsorbed ions and at high pressure,but much higher at low pressure than those of the electrode surface which should be minimized.In this sense the carbon materials previously reported.This can be explained most efficient ion adsorption is achieved in the pores perfectly by the highly exclusive ultram roporosity but low total pore adapted to the ion size.Theoretical studies have revealed that volumes (<1.0 cm3 g-)of MAC materials because the Co, the capacitance shows an oscillatory behavior as a function uptake at low pressure is determined by the volume of ultra of nar pore size in a theoretical slit ore.]The and the high-pressure CO capacity largely s found to exhibi equal or esp the repa als 0.76 ches pres on rge-s e applications. adsorbent should KAC is appro ma m spe e pore size ally have high CO2/N2 select d stability du ing repet tely twic of the KOH (espec orpt sorption cycles ow regene n energy solvated OH-in di tortion).Since ions can be adsorbed on both CsAC showed promis ng CO2 uptakes(1.52 mmol g)at typical pore walls in KOH electrolyte,there may be a contribution to due gas conditions (25 C and P(CO2):0.15 bar)w hile main the capacitance of KAC from both compact layers of ions.This aining low N2 uptakes (0.61 mmol g,<1/8 of the CO2 uptake) eth hep at 25 C and 1.0 bar(Figure 6c).Additionally,CsAC showed a CO2/N2 selectivity(calculated from the ratio of the initial slopes CsAC showed standard rectangular-like CV curves in KOH of N2 and CO2 adsorption isotherms)of 18 (Figure S14a,Sup- electrolyte at a very high scan rate of 500 mV s(Figure s13a Supporting Information).and preserved 73%of its specific n r e长g apacitance (162 F g)after increasing current density to the aim to test the recyclability of CsAC.four consecutive CO, 20 A g-1.These results reveal excellent po nerformance adsorption cycles were carried out at 25C.and nearly identical being indicative of the good characteristics of the carbon pore sotherms were obtained(Figure S14b,Supporting Informa- (i.e.,high unifo and short The a por h ion).With the the uch highe ostercherfyinededfor C ascribed L (Figure 50 this the h KOH retention ra showed a relative ffect.The capacit et MAC nergy co ng regeneration increases with pore size being attributed to the fast diffusion of presence of a well-developed ultramicropore network with narrow pore size distribution (diameter -0.76 nm)in CsAC results in a high utilization degree of the overall porosity and 2016 WILEY-VCH Verlag GmbH Co.KGaA.Weinheim wileyonlinelibrary.com 7

full paper © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 7 liquid electrolyte, and this value is one of the highest among carbon electrode materials (Table S2, Supporting Information). When evaluating the potential of a porous carbon for superca￾pacitor applications (especially in portable electronic devices), the specific volumetric capacitance is a more reliable parameter as compared to the gravimetric one. CsAC (packing density of ca 0.92 cm3 g−1 ) showed very high volumetric capacitances of 203 and 205 F cm−3 in KOH and EMImBF4, respectively. The ultrahigh capacitance properties can be better under￾stood by studying the relationship between pore and ion size. Results of the areal capacitance and retention ratio as a func￾tion of MAC material clearly pointed out a pore size effect (Figure 5e, please note that LiAC was not included because of its broad pore size distribution[25]). A maximum in specific areal capacitance is reached by KAC in KOH electrolyte, with signifi￾cantly lower values obtained for the rest of carbon materials. In contrast, the specific areal capacitance in EMImBF4 was found to monotonously increase with pore size, with CsAC showing the maximum normalized capacitance. Even though KAC and NaAC have very fine difference in pore sizes (≈0.66 vs 0.63 nm), the specific areal capacitance of the latter in KOH electro￾lyte is much larger than that of NaAC. These results can be explained in terms of pore size and electrolyte ion size (EMIm+: 0.76 nm, BF4 −: 0.45 nm, solvated K+: 0.31 nm, and solvated OH−: 0.35 nm). According to the equation of C = εA/d, the capacitance (C) of a supercapacitor electrode mainly depends on the electrode specific surface area (A), which must be as high as possible, and the distance (d) between the adsorbed ions and the electrode surface which should be minimized. In this sense, most efficient ion adsorption is achieved in the pores perfectly adapted to the ion size. Theoretical studies have revealed that the capacitance shows an oscillatory behavior as a function of nanopore size in a theoretical slit pore.[26] The capacitance versus pore size was found to exhibit two peaks located at the diameters equal to ion size or twice of that, respectively. CsAC possesses a uniform pore size (0.76 nm) that perfectly matches with that of EMIm+, thus leading to efficient ion adsorption and maximum specific areal capacitance.[4] The pore size of KAC is approximately twice that of the KOH ions (especially solvated OH− in distortion). Since ions can be adsorbed on both pore walls in KOH electrolyte, there may be a contribution to the capacitance of KAC from both compact layers of ions. This result is also in good agreement with the experimental results by Béguin and co-workers.[27] CsAC showed standard rectangular-like CV curves in KOH electrolyte at a very high scan rate of 500 mV s−1 (Figure S13a, Supporting Information), and preserved 73% of its specific capacitance (162 F g−1 ) after increasing current density to 20 A g−1 . These results reveal excellent power performance, being indicative of the good characteristics of the carbon pore system (i.e., high uniformity and short pore length) designed herein. The as-prepared carbons showed much higher capaci￾tance retention ratio in KOH than in IL (Figure 5f), and this may be ascribed to the high conductivity, low viscosity, and small ion size of the KOH electrolyte. The retention ratio also showed a pore size effect. The capacitance retention of MAC increases with pore size being attributed to the fast diffusion of ions in larger pores. Ragone plots (Figure S13b,c, Supporting Information) revealed remarkable energy densities values of 32.5 and 6.2 Wh kg−1 for CsAC in IL and KOH electrolytes, respectively. The cycling stability of CsAC against charge–dis￾charge cycles was investigated at 1 A g−1 in KOH (Figure S13d, Supporting Information). Remarkably, the specific capacitance of the electrode was maintained at ≈191 F g−1 (nearly 100% capacitance retention), even after 10 000 cycles. 2.4. CO2 Sorption Performance of MAC Materials CO2 capture has attracted considerable attention in recent years as CO2 is the main anthropogenic contributor to climate change. In consideration of the microporous characteristics of MAC, we carried out CO2 adsorption measurements at 1.0 and 20 bar (Figure 6). As reported in Table S3 (Supporting Infor￾mation), CsAC showed very high CO2 uptake values at 1.0 bar (6.77 and 5.20 mmol g−1 at 0 and 25 °C, respectively) well above than those reported for carbon materials under identical condi￾tions (Table S4, Supporting Information) and higher than those of metal-organic frameworks (MOFs)[28] and covalent organic frameworks (COFs)[29] that are also considered as good CO2 adsorbents. Figure 6c shows the CO2 adsorption isotherms of the MAC materials at 25 °C and 0–20 bar. RbAC exhibits the highest CO2 capacity, i.e., 9.63 mmol g−1 (42.4 wt%) at 25 °C and 20 bar. The trend of CO2 uptakes at 20 bar is in good agree￾ment with that of total pore volume. As shown in Table S5 (Sup￾porting Information), the CO2 uptakes of CsAC are much less at high pressure, but much higher at low pressure than those of the carbon materials previously reported. This can be explained by the highly exclusive ultramicroporosity but low total pore volumes (<1.0 cm3 g−1 ) of MAC materials because the CO2 uptake at low pressure is determined by the volume of ultra￾micropores,[7] and the high-pressure CO2 capacity largely cor￾relates to the volumes of micropores and narrow mesopores.[30] Therefore, the prepared MAC materials are more suitable to CO2 sorption at low pressure. For large-scale CO2 capture applications, an adsorbent should ideally have high CO2/N2 selectivity, good stability during repet￾itive adsorption–desorption cycles, and low regeneration energy. CsAC showed promising CO2 uptakes (1.52 mmol g−1) at typical flue gas conditions (25 °C and P(CO2): 0.15 bar) while main￾taining low N2 uptakes (0.61 mmol g−1, <1/8 of the CO2 uptake) at 25 °C and 1.0 bar (Figure 6c). Additionally, CsAC showed a CO2/N2 selectivity (calculated from the ratio of the initial slopes of N2 and CO2 adsorption isotherms) of 18 (Figure S14a, Sup￾porting Information),[31,32] this value being comparable (or even superior) than that of some nitrogen-doped carbons.[32,33] With the aim to test the recyclability of CsAC, four consecutive CO2 adsorption cycles were carried out at 25 °C, and nearly identical isotherms were obtained (Figure S14b, Supporting Informa￾tion). With the aim to investigate the energy needed for regen￾eration, we calculated the isosteric heat of adsorption (Qst) by applying the Clausius–Clapeyron equation to the CO2 adsorp￾tion isotherm data at 0 and 25 °C. As shown in Figure 6e, CsAC showed a relative low Qst (17–21 kJ mol−1 ) that envisages low energy consumption during regeneration. We believe that the presence of a well-developed ultramicropore network with narrow pore size distribution (diameter ≈0.76 nm) in CsAC results in a high utilization degree of the overall porosity and Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201601904 www.afm-journal.de www.MaterialsViews.com

器 www.afm-journal.de ViewS www.MaterialsViews.com (a) (b) -LiAC -RbAC LiAC RbAC -NaAC◆CsAC -NaAC CsAc 一KAC -KAC 4 3 2 8 8 8.00.20.40.60.8 10 %0 0.20.40.60.81.0 Pressure(bar） Pressure(bar) (c) (d) 10 6 。-LiAC 一N。 CsAC at 25'C co 5.20 -KAC RbAC ◆-CsAC 2 8 0.61 0 0 51015202530 .0 0204060810 Pressure(bar) Pressure(bar) (e) () 25 35 。-LiAC 20 20 Na 15 -0-0-0-0-0-0 15 -RbAC 10 ◆-CsAC 5 -CsAC % 1 2 3 4 0 10152025 co,uptake(mmol g'） Pressure(bar) surface area of the carbon material.These characteristics are of water vapor at very low relative pressures (7.7 mmol g responsible for excellent CO2 adsorption performance at room at 10 mbar).34 As long as the partial pressure of H2o is kept temperature and ambient pressure. below 10 mbar.H2O adsorption may not be expected to inter- In practice,flue gas is a mixture of mostly N2.CO2.and fere with CO,adsorption.Over 10 mbar,a sharp increase in the H,O,while its exact composition depends on the design of amount of H,O adsorbed was observed,and then the presence the power plant and the source of natural gas or coal.H2O is of water in the pores will lead to a decrease of the accessible strongly adsorbed n many adsorbents (zeolite)and thus volume causing a decrease of CO2 adsorption capacity.It is also can e of H2O in flue he fo min eis ay: therms over so the fu CsAC)is very high capa orption to ther cor b H.ophon pore rf 0 ted that th sorption to , until pressures above 10 mbar(corresponding to a relative pres in the adsorber sure of about 0.33).In contrast,zeolite 13X,intensively studied for CO2 capture,presents much higher adsorption capacity kinetic separation of CO2 from H2O. 8 wileyonlinelibrary.com 2016 WILEY-VCH Verlag GmbH Co.KGaA,Weinheim

full paper 8 wileyonlinelibrary.com © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim surface area of the carbon material. These characteristics are responsible for excellent CO2 adsorption performance at room temperature and ambient pressure. In practice, flue gas is a mixture of mostly N2, CO2, and H2O, while its exact composition depends on the design of the power plant and the source of natural gas or coal. H2O is strongly adsorbed on many adsorbents (e.g., zeolites), and thus, its presence can cause a reduction in the adsorption capacity of CO2. Figure 6f represents the water vapor adsorption iso￾therms over MAC materials at 25 °C. Although the capacity of water vapor (20.54 mmol g−1 for CsAC) is very high compared to that of CO2 (5.20 mmol g−1), it has to be pointed that there is negligible H2O adsorption on hydrophobic carbon pore surface until pressures above 10 mbar (corresponding to a relative pres￾sure of about 0.33). In contrast, zeolite 13X, intensively studied for CO2 capture, presents much higher adsorption capacity of water vapor at very low relative pressures (7.7 mmol g−1 at 10 mbar).[34] As long as the partial pressure of H2O is kept below 10 mbar, H2O adsorption may not be expected to inter￾fere with CO2 adsorption. Over 10 mbar, a sharp increase in the amount of H2O adsorbed was observed, and then the presence of water in the pores will lead to a decrease of the accessible volume causing a decrease of CO2 adsorption capacity. It is also important to note that the partial pressure of H2O in flue gases is always over 10 mbar, especially in those after wet desulphuri￾zation. So the flue gases would likely need to be dried to below 10 mbar for H2O adsorption to remain negligible. Another con￾siderable method is appropriately controlling the adsorption time for CO2 sorption to maximize the concentration of CO2 in the adsorbents due to the difference of diffusivity between CO2 and H2O.[35] The higher diffusivity of CO2 will facilitate the kinetic separation of CO2 from H2O. Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201601904 www.afm-journal.de www.MaterialsViews.com Figure 6. a) CO2 adsorption isotherms at 0 °C and 1.0 bar. b) CO2 adsorption isotherms at 25 °C and 1.0 bar. c) CO2 adsorption isotherms at 25 °C and 20 bar. d) CO2 and N2 adsorption isotherms on CsAC at 25 °C. e) CO2 heats of adsorption on MACs. f) Water vapor adsorption isotherms at 25 °C

器 www.afm-journal.de www.MaterialsViews.com 3.Conclusion mass of the active materials was 2.0mgfor each electrode.The model A simple ultramicropore size tuning method for carbon mate. FULL rials was proposed herein.The pore size can be finely tuned in the range of 0.60-0.76 nm.The pore size tuning resulted from EMImBF4.The electrochemical measurements were carried on a the varying activating strength and ion sizes of the alkali metals e specific capac from Lit to Cst.The carbon pared by direct pvrol ysis of alkai salt of carborylic phenolic resins showed highly PAPER developed and uniform short le materials showed c ⑦ pe2dt20sfarnionicliquidcdecto spe e as a ehinporeandio n si 部0 me p capaan orhe crbo orption capacity of 5.20 g at Av (V)was the full regenerability the total mass of active materialsin the cell. for four consecutive cycles.This work paves the way for a new route to finely tuning ultramicropores size at the sub-angstrom level in carbon materials.It is anticipated that these intriguing carbon materials might also find applications as molecular E=号×Cmxv2 sieves,catalysts,battery electrodes,and water/air filters. p-E (3) 4.Experimental Section where the C. V and t w 。 e of the of MAC Materials: pacitor cell before discharge and the time spent in discharge,respectively. 6mL and stirred forh to form a pale yellow clear solution. solution was then solidified at 120C for 24 h.The resulting solid was Covernight and for 2h with a he Supporting Information ewheddndeo Supporting Information is available from the Wiley Online Library or ze rom the author water to neutrality. renMAC Materi Microscopic morphology of the microscope (EM2100.)Surface chemical Acknowledgements determined by X-ray energy dispersive spectr he Advance diffract ith Cu Ka radiation In situ XRD )ndDistinguished Young Scientist Foundation of Shandong d system Received April 16 2016 Revised:July 11,2016 on MID Published online: mass spectrometer (heating rate 20 C min-1,helium flow). Rama Ho 196 s were measu ed at usin a surface area and porosity analyzer (ASAP2020M.Micron ,S.Murali,M.D.Stolle J.Gan eritic 43 USA).N2 and CO2 gases with super high purity(99.999%)were used for E A 2011.3321537:bF.8 The carbon sample 2014.262219. c)L.Borchardt,M.Oschatz,S.Kaskel,Mater.Horiz.2014,1,157; calculated using the N adsorption isotherm data within the relative d)A.-H.Lu,G.-P.Hao.Annu.Rep.Prog.Chem.,Sect.A:Inorg. ressure.Total pore volume was obtained at a Chem.2013,109,484;e)Y.Xia,R.Mokaya,G.S.Walker,Y.Zhu, Adv.Energy Mater.2011.1,678. ative pres Micropore ce area and um ow pressure (0-1.0bar)were arried on the ASAP2020M analyzer.The measurements of high. 2006.313.1760. ressure CO,ad orpton and water vapor adsorption were performed or [4]C.Largeot,C.Portet,J.Chmiola,P.-L Taberna,Y.Gogotsi, P.Simon,J.Am.Chem.Soc.2008,130,2730. [5]a)N.P.Wickramaratne,M.Jaroniec.J.Mater.Chem.A2013,1.112; electrodes were prepared by mixing 95 wt%carbon materials and b)G.-P.Hao,Z.Y.Jin,Q.Sun,X.-Q.Zhang.J-T.Zhang.A.-H.Lu, S.Kim,M.S.Kang. 2016 WILEY-VCH Verlag GmbH Co.KGaA,Weinheim wileyonlinelibrary.com 9

full paper © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 9 3. Conclusion A simple ultramicropore size tuning method for carbon mate￾rials was proposed herein. The pore size can be finely tuned in the range of 0.60–0.76 nm. The pore size tuning resulted from the varying activating strength and ion sizes of the alkali metals from Li+ to Cs+. The carbon materials prepared by direct pyrol￾ysis of alkali salts of carboxylic phenolic resins showed highly developed and uniform short length ultramicroporosity. The prepared carbon materials showed ultrahigh specific capaci￾tances of 205 F cm−3 in ionic liquid electrolyte as a result of a perfect match in pore and ion sizes. The CsAC material showed superior CO2 adsorption capacity of 5.20 mmol g−1 at 25 °C and 1.0 bar, high CO2-to-N2 selectivities and full regenerability for four consecutive cycles. This work paves the way for a new route to finely tuning ultramicropores size at the sub-angstrom level in carbon materials. It is anticipated that these intriguing carbon materials might also find applications as molecular sieves, catalysts, battery electrodes, and water/air filters. 4. Experimental Section Preparation of MAC Materials: In a typical synthesis, 2,4-dihydroxybenzoic acid (0.5 g, 3.2 mmol), alkali hydroxide (3.5 mmol), and formaldehyde (0.53 g, 37 wt%, 0.64 mmol) were dissolved into 6 mL H2O, and stirred for 1 h to form a pale yellow clear solution. The solution was then solidified at 120 °C for 24 h. The resulting solid was dried at 100 °C overnight and carbonized at 900 °C for 2 h with a heating ramp of 3 °C min−1 in argon. Finally, the alkali metal ion-activated carbon materials were liberated by washing with diluted HCl and deionized water to neutrality. Characterization of MAC Materials: Microscopic morphology of the prepared carbon materials were observed with a scanning electron microscope (Sirion 200 FEI Netherlands) and a transmission electron microscope (JEM2100, JEOL, Japan). Surface chemical properties were determined by X-ray energy dispersive spectroscopy (EDS, BRUKER AXS) and X-ray photoelectron spectroscopy (XPS, Escalab 250, USA). XRD patterns of the carbon materials were conducted on a Bruker D8 Advance diffractometer with Cu Kα radiation. In situ XRD patterns during the pyrolysis of PR-COOK were collected on a PANalytical X’Pert Pro system operated at 40 kV and 40 mA current with Cu Kα source under N2. TG-MS studies were performed on a thermogravimetric analyzer (NETZSCH STA 409 thermobalance) coupled to Balzers MID mass spectrometer (heating rate 20 °C min−1 , helium flow). Raman spectra were collected by a LabRAM HR800 from JY Horiba. N2 adsorption–desorption isotherms were measured at liquid nitrogen temperature (−196 °C) and CO2 adsorption was performed at 0 °C using a surface area and porosity analyzer (ASAP2020M, Micromeritics, USA). N2 and CO2 gases with super high purity (99.999%) were used for the physisorption measurements. The carbon samples were degassed at 350 °C for 6 h under turbomolecular vacuum before sorption measurements. Brunauer–Emmett–Teller (BET) surface area was calculated using the N2 adsorption isotherm data within the relative pressure ranging from 0.05 to 0.25. Total pore volume was obtained at a relative pressure of 0.995. Micropore surface area and micropore volume were calculated by the t-plot method. CO2 sorption of MAC materials at low pressure (0–1.0 bar) were determined by a static adsorption method carried on the ASAP2020M analyzer. The measurements of high￾pressure CO2 adsorption and water vapor adsorption were performed on an intelligent gravimetric analyzer. Fabrication of Electrodes and Electrochemical Measurements: Working electrodes were prepared by mixing 95 wt% carbon materials and 5 wt% polytetrafluoroethylene (PTFE) binders, pressing the mixture onto nickel foam at 15 MPa, and then drying at 120 °C for 10 h. The mass of the active materials was 2.0 mg for each electrode. The model capacitors were assembled in a glove box filled with argon (Mikrouna Universal 2440, H2O and O2 <1 ppm) by facing two electrodes sandwiched with a fiber separator for the ionic liquid electrolyte of EMImBF4. The electrochemical measurements were carried on a CHI660D electrochemical testing station (Chenhua Instruments Co. Ltd., Shanghai). The specific capacitance was calculated by the following equation 4 C I t m ∆V m = × × (1) where Cm (F g−1 ) was the gravimetric specific capacitance of the carbon samples, I (A) was the discharge current, t (s) was the time spent in discharge, ΔV (V) was the potential window of the cell, and m (g) was the total mass of active materials in the cell. Energy density (E) and powder density (P) could be calculated from the galvanostatic charge/discharge test using the equations of 1 8 2 E C = × m × V (2) P E t = (3) where the Cm, V, and t were the gravimetric specific capacitance of the carbon materials, the voltage of a supercapacitor cell before discharge, and the time spent in discharge, respectively. Supporting Information Supporting Information is available from the Wiley Online Library or from the author. Acknowledgements The authors are grateful for the financial supports by National Natural Science Foundation of China (NSFC51302156, 21476264, 21576158 and 21576159) and Distinguished Young Scientist Foundation of Shandong Province (JQ201215). Received: April 16, 2016 Revised: July 11, 2016 Published online: [1] a) Y. Zhu, S. Murali, M. D. Stoller, K. J. Ganesh, W. Cai, P. J. Ferreira, A. Pirkle, R. M. Wallace, K. A. Cychosz, M. Thommes, D. Su, E. A. Stach, R. S. Ruoff, Science 2011, 332, 1537; b) F. Beguin, V. Presser, A. Balducci, E. Frackowiak, Adv. Mater. 2014, 26, 2219; c) L. Borchardt, M. Oschatz, S. Kaskel, Mater. Horiz. 2014, 1, 157; d) A.-H. Lu, G.-P. Hao, Annu. Rep. Prog. Chem., Sect. A: Inorg. Chem. 2013, 109, 484; e) Y. Xia, R. Mokaya, G. S. Walker, Y. Zhu, Adv. Energy Mater. 2011, 1, 678. [2] P. Simon, Y. Gogotsi, Acc. Chem. Res. 2012, 46, 1094. [3] J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon, P. L. Taberna, Science 2006, 313, 1760. [4] C. Largeot, C. Portet, J. 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