. Corni et al Jounal of the European Ceramic Sociery 28(2008)1353-1367 1359 have excellent long term stability and also due to the versatile low bodies and objects of complex 3D shape using EPd of nature of the technology for direct conversion of chemical energy silica nanoparticles in aqueous suspensions. However, numerous to electrical energy materials can be deposited by EPD starting from water-based or In general, a solid oxide fuel cell device consists of a repeat- non-aqueous suspensions of nanoparticles. For example nanos- ing stack of multiple single fuel cells. In order to render SOFCs tructured BaTiO3 and Eu-doped BaTiO3 thin films have been economically competitive, however, it is fundamental to sig- recently reported, which were produced by EPD of nanoparti nificantly reduce the cost of materials and fabrication. For this cles from acetylacetone suspensions, 24 aqu reason EPD has been progressively considered for the fabrica- and ethanol suspensions. 26, 27 Zinc oxide nanoparticles have tion of cathode-and anode-supported solid oxide fuel cells of been deposited from aqueous suspensions, isopropyl alcohol both planar and tubular geometry. Several recent papers describe suspensions and 2-propanol suspensions. 30 The produc the use of EPD in this field2-12 and a complete review of the tion of nanostructured zirconia coatings by EPD has been developments achieved so far has been written by Besra and reported both from aqueous suspensions 31, 32 to pro uce den- tal crowns and from ethanol suspensions to produce thermal From these studies it has emerged that the relative advan- barrier coatings tages of EPD in the production of SoFCs are the ability to: Moreover a wide range of dense, nanostructured fund (a) deposit coatings on substrates of any shape,(b)control the tional films have been produced by electrophoretic deposition deposition conditions thus being able to prepare porous coat- of nanoparticles. Mahajan et al uce ing as electrode and dense coating as electrolyte, (c)obtain europium oxide(Eu2O3) thin films and noticed that the films laminate structures of electrodes and electrolyte and (d)pro- optical properties varied with deposit morphology: translucent, duce Ni-yttria stabilized zirconia (YSZ) cermets(anodes) by when there was a uniform size and distribution of the microstruc electrophoretic co-deposition. Yttria-stabilized zirconia (YSz) ture, and opaque, when there was a marked anisotropy of the by far the most popular material used as electrolyte in SOFCs size and distribution of the constituents of the microstruc- anks to its exceptional combination of properties such as high ture. The deposition of nanostructured titania films by EPD chemical and thermal stability and pure ionic conductivity over has been carried out by several groups. 35-14 For example a wide range of conditions. Also Lao. 3 Sro. 17Gao. 3Mgo 1702.83 Dittrich et al. 35, 36 produced TiO2 coatings with different (LSGM) has been employed to produce intermediate tempera- porosity, systematically changed by pressing, in order to opti- ture solid oxide fuel cells (IT-SOFCs). EPD has been also mize the electron diffusion. These coatings present potential shown to be effective to deposit glass-ceramic layers, which are applications in many fields, such as batteries, displays, photo- used as sealant material in some SOFCs designs. 22 Moreover catalysis and solar energy conversion systems. Manriquez and because of the short formation times and the simple equipment Godinez u deposited Ti(m)-doped nanocrystalline TiO2 films needed the use of EPD should simplify the fabrication process on optically transparent electrodes. Valatka and Kulesius41 of SoFC stacks with complex design architecture achieving fur- deposited nanosized titania films on stainless steel and then ther cost reductions. In spite of the progress achieved recently they used the decoloration of methylene blue dye to evaluate in this area, many problems remain unsolved as described ear- the photoelectrocatalytic activity of the coatings. Hydroxyap er by Zhitomirsky and Petric, 2 who underlined that major atite(HA)nanoparticles have been extensively deposited by difficulties are linked to the selection of adequate solvents and means of EPD 42-146 Other nanoparticles were deposited by of the components of the binder-dispersant-solvent system, the an ethanol suspension 69 silicon carbide. 141 ceric<48 powder additives, in particular concerning the chemical compatibility EPD such as: nanosized lead zirconate titanate(Pzt) powder in solubility of the binder, the viscosity and the electrical resistin- pentoxide, 49 hydrous ruthenium oxide, 50, 5I gamma ferric broaden the range of applications of EPD in SOFC technology. and yttria-stabilized zirconia anotubes 159 1 0ve-155nickel ity of the suspensions. Therefore more studies are needed and a oxide, 52 nickel, 53, 54 iron, 53 aluminium, 53 better understanding of the process has to be achieved in order to ferrite, 56 silica, 57, 58 titania polyimide161 Recently, research has been carried out on the deposition of 3.3. Nanotechnology polymeric nanocomposite coatings. For example, polythiophene and metal oxide (alumina, titania and silica) nanocompos 3.3.1. EPD of nanoparticle ites have been electrophoretically deposited from an ethanol The electrophoretic deposition of ceramic nanoparticles(size suspension by Vu et al. 63 They obtained thin films of con- 100 nm)is a special colloidal processing method employed to ducting polymer/metal oxide with a core-shell structure that produce a variety of materials, including monolithic ceramics, can be employed in electronic devices. Kim et al. 6- deposited well as ceramic laminates and ceramic matrix composites of poly(methyl methacrylate)-BaTiO3 nanocomposite coatings ceramic coatings and films, functionally graded materials, as from an isopropyl alcohol/acetone solvent mixture on copper high microstructural homogeneity. Previous work on EPD of foils. The composite films presented a uniform microstructure nanoparticles has been reviewed comprehensively elsewhere& without particle agglomeration. Furthermore, the deposition of and only selected recent papers published in the last 2 years are metal-ceramic nanocomposite coatings has also been inves therefore covered in this section tigated. For example, nanostructured Ni-wC-Co composite Tabellion and Clasen07 have discussed previous work on coatings have been produced by means of EPD on nickel the fabrication of large components, free standing objects, hol- plated stainless steel substrates. These composite coatingsI. Corni et al. / Journal of the European Ceramic Society 28 (2008) 1353–1367 1359 have excellent long term stability and also due to the versatile nature of the technology for direct conversion of chemical energy to electrical energy.109–111 In general, a solid oxide fuel cell device consists of a repeat￾ing stack of multiple single fuel cells. In order to render SOFCs economically competitive, however, it is fundamental to sig￾nificantly reduce the cost of materials and fabrication. For this reason EPD has been progressively considered for the fabrica￾tion of cathode- and anode-supported solid oxide fuel cells of both planar and tubular geometry. Several recent papers describe the use of EPD in this field112–121 and a complete review of the developments achieved so far has been written by Besra and Liu.5 From these studies it has emerged that the relative advan￾tages of EPD in the production of SOFCs are the ability to: (a) deposit coatings on substrates of any shape, (b) control the deposition conditions thus being able to prepare porous coat￾ing as electrode and dense coating as electrolyte, (c) obtain laminate structures of electrodes and electrolyte and (d) pro￾duce Ni-yttria stabilized zirconia (YSZ) cermets (anodes) by electrophoretic co-deposition. Yttria-stabilized zirconia (YSZ) is by far the most popular material used as electrolyte in SOFCs thanks to its exceptional combination of properties such as high chemical and thermal stability and pure ionic conductivity over a wide range of conditions. Also La0.83Sr0.17Ga0.83Mg0.17O2.83 (LSGM) has been employed to produce intermediate tempera￾ture solid oxide fuel cells (IT-SOFCs).118 EPD has been also shown to be effective to deposit glass-ceramic layers, which are used as sealant material in some SOFCs designs.122 Moreover because of the short formation times and the simple equipment needed the use of EPD should simplify the fabrication process of SOFC stacks with complex design architecture achieving fur￾ther cost reductions. In spite of the progress achieved recently in this area,5 many problems remain unsolved as described ear￾lier by Zhitomirsky and Petric,123 who underlined that major difficulties are linked to the selection of adequate solvents and additives, in particular concerning the chemical compatibility of the components of the binder-dispersant-solvent system, the solubility of the binder, the viscosity and the electrical resistiv￾ity of the suspensions. Therefore more studies are needed and a better understanding of the process has to be achieved in order to broaden the range of applications of EPD in SOFC technology. 3.3. Nanotechnology 3.3.1. EPD of nanoparticles The electrophoretic deposition of ceramic nanoparticles (size <100 nm) is a special colloidal processing method employed to produce a variety of materials, including monolithic ceramics, ceramic coatings and films, functionally graded materials, as well as ceramic laminates and ceramic matrix composites of high microstructural homogeneity. Previous work on EPD of nanoparticles has been reviewed comprehensively elsewhere8 and only selected recent papers published in the last 2 years are therefore covered in this section. Tabellion and Clasen107 have discussed previous work on the fabrication of large components, free standing objects, hol￾low bodies and objects of complex 3D shape using EPD of silica nanoparticles in aqueous suspensions. However, numerous materials can be deposited by EPD starting from water-based or non-aqueous suspensions of nanoparticles. For example nanos￾tructured BaTiO3 and Eu-doped BaTiO3 thin films have been recently reported, which were produced by EPD of nanoparti￾cles from acetylacetone suspensions,124 aqueous suspensions125 and ethanol suspensions.126,127 Zinc oxide nanoparticles have been deposited from aqueous suspensions,128 isopropyl alcohol suspensions129 and 2-propanol suspensions.130 The produc￾tion of nanostructured zirconia coatings by EPD has been reported both from aqueous suspensions131,132 to produce den￾tal crowns132 and from ethanol suspensions to produce thermal barrier coatings.133 Moreover a wide range of dense, nanostructured func￾tional films have been produced by electrophoretic deposition of nanoparticles. Mahajan et al.134 produced nanocrystalline europium oxide (Eu2O3) thin films and noticed that the films optical properties varied with deposit morphology: translucent, when there was a uniform size and distribution of the microstruc￾ture, and opaque, when there was a marked anisotropy of the size and distribution of the constituents of the microstruc￾ture. The deposition of nanostructured titania films by EPD has been carried out by several groups.135–141 For example Dittrich et al.135,136 produced TiO2 coatings with different porosity, systematically changed by pressing, in order to opti￾mize the electron diffusion. These coatings present potential applications in many fields, such as batteries, displays, photo￾catalysis and solar energy conversion systems. Manr´ıquez and God´ınez140 deposited Ti(III)-doped nanocrystalline TiO2 films on optically transparent electrodes. Valatka and Kulesius141 deposited nanosized titania films on stainless steel and then they used the decoloration of methylene blue dye to evaluate the photoelectrocatalytic activity of the coatings. Hydroxyap￾atite (HA) nanoparticles have been extensively deposited by means of EPD.142–146 Other nanoparticles were deposited by EPD such as: nanosized lead zirconate titanate (PZT) powder in an ethanol suspension,69 silicon carbide,147 ceria,148 vanadium pentoxide,149 hydrous ruthenium oxide,150,151 gamma ferric oxide,152 nickel,153,154 iron,153 aluminium,153 silver,155 nickel ferrite,156 silica,157,158 titania nanotubes,159,160 polyimide161 and yttria-stabilized zirconia.162 Recently, research has been carried out on the deposition of polymeric nanocomposite coatings. For example, polythiophene and metal oxide (alumina, titania and silica) nanocompos￾ites have been electrophoretically deposited from an ethanol suspension by Vu et al.163 They obtained thin films of con￾ducting polymer/metal oxide with a core-shell structure that can be employed in electronic devices. Kim et al.164 deposited poly(methyl methacrylate)-BaTiO3 nanocomposite coatings from an isopropyl alcohol/acetone solvent mixture on copper foils. The composite films presented a uniform microstructure without particle agglomeration. Furthermore, the deposition of metal–ceramic nanocomposite coatings has also been inves￾tigated. For example, nanostructured Ni–WC–Co composite coatings have been produced by means of EPD on nickel￾plated stainless steel substrates.165 These composite coatings