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PtRu and PtRuMo electrocatalysts supported on N-doped graphene nanoplatelets (N-GNPs) were synthesized by a polyol method and utilized as anodes in polymer electrolyte membrane fuel cells (PEMFCs) to measure their CO tolerance and stability. A higher structural stability of the N-GNP supported catalysts, presenting a lower metal loss and a lower particle growth than PtRu/C was observed. Tests in PEMFCs indicated both a higher CO tolerance and a higher electrochemical stability of N-GNP supported PtRu and PtRuMo catalysts than a commercial conventional carbon black (CB) supported PtRu.

To prevent sintering of carbon supported metal nanoparticles during high temperature annealing in reductive conditions, Pt-Sn nanoparticles were coated with MgO. The agglomeration of Pt-Sn particles upon thermal annealing was significantly inhibited with a MgO shell. The presence of the oxide shell gave rise to a more homogeneous microstructure and a better electrochemical stability.

Platinum and platinum-based electrocatalysts for the methanol oxidation reaction (MOR) are commonly used as the anode material in direct methanol fuel cells (DMFCs). Photo-oxidation promoted by ultraviolet and visible light is a promising method to increase the catalytic activity of DMFC anode electrocatalysts. Photocatalytic and electrocatalytic methanol oxidation can be coupled by addition of TiO2, a semiconductor photocatalyst, to Pt. In the presence of TiO2, an increase of the MOR activity of Pt-based electrocatalysts takes place also in dark conditions. This review deals with the methanol photo-oxidation on Pt/TiO2 catalysts, highlighting the effect of TiO2 morphology, nanoparticles, or 1D nanostructures, on the MOR activity under illumination. Comparison of reaction mechanisms in the presence and the absence of light are presented, and the roles of Pt and TiO2 during electrochemical and photochemical reactions are discussed.

Pt electrocatalysts supported on pristine graphene nanosheets (GNS) and nitrogen-doped graphene nanoplatelets (N-GNP) were prepared through the ethylene glycol process, and a comparison of their CO tolerance and stability as anode materials in polymer electrolyte membrane fuel cells (PEMFCs) with those of the conventional carbon (C)-supported Pt was made. Repetitive potential cycling in a half cell showed that Pt/GNS catalysts have the highest stability, in terms of the highest sintering resistance (lowest particle growth) and the lowest electrochemically active surface area loss. By tests in PEMFCs, the Pt/N-GNP catalyst showed the highest CO tolerance, while the poisoning resistance of Pt/GNS was lower than that of Pt/C. The higher CO tolerance of Pt/N-GNP than that of Pt/GNS was ascribed to the presence of a defect in graphene, generated by N-doping, decreasing CO adsorption energy.

PdNi electrocatalysts supported on carbon were used as anode materials for methane oxidation in alkaline direct methane fuel cells (ADMEFCs). The electrocatalysts were successfully synthesized by the NaBH4 reduction method. X-ray diffraction measurements showed the formation of non-alloyed Pd in the face- centered cubic (FCC) structure for all materials and formation of NiO and Ni(OH)2 species. TEM images showed that the metal particles are well dispersed on the support with small agglomeration regions. Information about the surface structure of the catalyst were obtained by Raman spectra, mainly confirming the presence of Ni(OH)2. The species observed by DEMS, that is, methanol (m/z = 32), CO2 (m/z = 44) and potassium formate (m/z = 84) were confirmed by FTIR, which also showed the presence of a high amount of carbonate in the methane oxidation products of the ADMEFC with Pd50Ni50/C as the anode catalyst. Tests in ADMEFCs showed that the dependence of the maximum power density on nickel content in the catalysts goes through a maximum value of 13.5 μW cm−2 at 50 at% Ni. Moreover, the amount of produced methanol decreases with increasing Ni content in the PdNi/C catalysts. Both these results can be explained by the enhanced methanol oxidation in the presence of nickel.

The application of intermetallic compounds in heterogeneous catalysis had a significant boost during the last decade. Notwithstanding the advantages related to the use of intermetallics in catalysis, random alloys, more easy to prepare, are commonly used as catalysts in low temperature polymer electrolyte membrane fuel cells (LT-PEMFC). In various papers, however, the use of Pt- and Pd-based intermetallics in LT-PEMFCs is reported. In this work an overview of the effect of the crystal structure ordering on the activity for oxygen reduction and stability of fuel cell catalysts is discussed, by comparing ordered and disordered structures with the same A/M (A = Pt, Pd; M = first row transition metal) atomic ratio and ordered structures with different A content.

Nitrogen-doped carbon materials represent a significant part in the field of energy conversion and storage technologies such as proton exchange membrane fuel cells and supercapacitors. The achievement of these materials by sustainable N- and C-containing natural resources using various methods, such as pyrolysis, hydrothermal and ionothermal carbonization is presented. The application of these novel materials as nonprecious catalysts and catalyst supports for low temperature fuel cells is discussed.

Carbon supported platinum is commonly used as anode and cathode catalyst in low-temperature fuel cells. The need of modify the chemical characteristics of the supported catalyst has emerged due to several factors, such as reducing the price of the active catalyst and increasing its activity, selectivity, and long-term stability. Thus, pure Pt is now rapidly being replaced by oxide promoted Pt and Pd or Pt- and Pd-based alloy catalysts in low-temperature fuel cells. In addition to the chemical characteristics of the catalysts, many studies on nanocatalysts have been addressed to correlating the catalytic activity with some physical characteristics of supported fuel cell catalysts. This review article examines the role played by metal particle size, inter-particle distance and metal loading on the support in determining the catalytic activity of supported catalysts.

The high availability and low cost of Fe make it an interesting element for use in non-precious Pt-free catalysts and Pt-based catalysts for low-temperature fuel cells. Pt–Fe compounds can present three crystal structures, these are a disordered fcc PtxFe alloy and two ordered intermetallic alloys (fcc Pt3Fe and fct PtFe types). Fe-containing Pt-based binary and ternary catalysts in the different crystal structures have been tested both as anode and cathode materials in low-temperature acid fuel cells. In this work an overview of the application of Fe-containing catalysts as cathode materials for oxygen reduction and as anode materials for methanol and ethanol oxidation in low-temperature polymer electrolyte fuel cells fuelled with hydrogen or low molecular weight alcohols, is presented. Moreover, the stability of iron in Pt-based binary and ternary catalysts towards dissolution in acid medium is discussed.

Recently, the feasibility of using composite metal–carbon, metal–polymer, polymer–carbon, polymer–polymer and carbon–carbon materials in microbial fuel cells (MFCs) has been investigated. These materials have been tested as MFC anode catalyst (microorganism) supports, cathode catalysts and membranes. These hybrid materials, possessing the properties of each component, or even with a synergistic effect, would present improved characteristics with respect to the bare components. In this paper we present an overview of the use of these composite materials in microbial fuel cells. The characteristics of the composite materials as well as their effect on MFC performance were compared with those of the individual component and/or the conventionally used materials.

The effect of operational parameters on the performance of PEMFCs by using serpentine flow field channels with different (rectangular and trapezoidal) cross-section shape has been investigated. More than cell temperature and pressure, reactant humidification temperature (Tha,c) has a significant influence on the effect of serpentine channels with trapezoidal cross-section on cell performance. The high capability of water removal by serpentine channels with trapezoidal cross-section positively affects the fuel cell performance when the water content in the system is high, as in the case of the reactant humidification temperature higher than cell temperature (Tc). On the contrary, when the water content in the cell is low, as in the case of Tha,c = Tc, the high ability of water removal of serpentine channels with trapezoidal cross-section results in a less effective membrane/cathode hydration. Conversely, the effect of Tha,c on the performance of the cell with serpentine channels with rectangular cross-section is negligible.

In view of possible use as cathode materials in polymer electrolyte membrane fuel cells, the electrocatalytic activity of palladium–cobalt catalysts for oxygen reduction has been investigated in acid medium. In this minireview, the effect of structural characteristics, such as degree of alloying, particle size and palladium segregation on the alloy surface to form a core–shell system, on the electrocatalytic activity of palladium–cobalt catalysts for oxygen reduction is discussed.

Highly dispersed catalysts on a conductive support, commonly platinum and platinum-based catalysts, are used as electrode materials in low-temperature fuel cells. Carbon blacks are commonly used as fuel cell catalysts supports, but their properties are not completely satisfactory. Thus, in the last years carbon black alternative materials such as nanostructured carbons, ceramic and polymer materials have been proposed as fuel cell catalyst supports. Very recently, in consideration of their high surface area, high conductivity, unique graphitized basal plane structure and potential low manufacturing cost, graphene nanosheets have been investigated as a support for low-temperature fuel cell catalysts. This paper presents an overview of graphene nanosheets used as supports for fuel cell catalysts. In particular, the catalytic activity and durability of catalysts supported on graphene are compared with those of catalysts supported on the commonly used carbon blacks and on carbon nanotubes, that is, on rolled graphene.

The electrode stability is a key issue for the development of conventional hydrogen fuelled and direct internal reforming (DIR) molten carbonate fuel cells (MCFCs). While for conventional MCFC anodes the stability problem has been addressed by the addition of Al or Cr to Ni, the problems of the dissolution of the NiO cathode and of the deactivation of DIR-MCFC anodes have not been fully resolved too. This review reports recent improvements in the chemical and physicochemical stability of cathode and anode materials in MCFCs and DIR-MCFCs, respectively.

Rare earth-based materials can play different roles in fuel cell systems. These compounds can be used as catalysts, co-catalysts and electrolytes additives in different types of fuels cells. In particular, a promising acid direct methanol fuel cell can be obtained using rare earth-based materials as both anode and cathode co-catalysts and proton exchange membrane additive. In this work an overview of the use of rare earth-based materials in low-temperature fuel cells is presented.

An empirical model is proposed to evaluate the contribution of alloyed and non-alloyed tin in Ptz-Sn/C catalysts to the performance of direct ethanol fuel cells (DEFCs). The model is based on the presence of SnO2 and a Pt(1−x)Sx solid solution in the bimetallic catalysts. The model predicts the dependence of the performance of a single DEFC on the total Sn content and the degree of alloying of Ptz-Sn/C catalysts used as the anode material.

Highly dispersed platinum or platinum-based catalysts on a conductive support are commonly used as electrode materials in low-temperature fuel cells. The performance and, in particular, the stability of these catalysts strongly depend on the characteristics of the support. Being the use of plain carbon, ceramic or polymer materials not completely satisfactory, in the last years hybrid polymer–carbon, ceramic–carbon and polymer–ceramic materials have been proposed as fuel cell catalyst supports. These hybrid materials, possessing the properties of each component, or even with a synergistic effect, would present improved characteristics with respect to the bare components. In this paper we present an overview of these hybrid materials as low-temperature fuel cell catalyst supports. The improved characteristics of the mixed supports with respect to the individual component and their effect on the electrochemical activity are highlighted.

Platinum–ruthenium catalysts are widely used as anode materials in polymer electrolyte fuel cells (PEMFCs) operating with reformate gas and in direct methanol fuel cells (DMFCs). Ruthenium dissolution from the Pt–Ru anode catalyst at potentials higher than 0.5 V vs. DHE, followed by migration and deposition to the Pt cathode can give rise to a decrease of the activity of both anode and cathode catalysts and to a worsening of cell performance. A major challenge for a suitable application of Pt–Ru catalysts in PEMFC and DMFC is to improve their stability against Ru dissolution. The purpose of this paper is to provide a better knowledge of the problem of Ru dissolution from Pt–Ru catalysts and its effect on fuel cell performance. The different ways to resolve this problem are discussed.

To evaluate the effect of the alloy phase characteristics on the ethanol oxidation activity, carbon supported (PtSnPd) alloy /SnO 2 catalysts were prepared and their electrocatalytic activity compared with that of carbon supported (PtSn) alloy /SnO 2 . Pt–Sn–Pd/C samples in the atomic ratio (1:1:0.3) and (1:1:1) were characterized by energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD analysis shows the presence of fcc Pt reflexions, shifted to lower angles, and SnO 2 reflexions. By comparison with the XRD patterns of carbon supported Pt–Sn (1:1) and Pt–Pd (3:1) samples, prepared by the same method, the formation of ternary PtSnPd alloys is postulated. The crystallite size of the ternary catalysts is smaller than that of both binary Pt–Sn/C (1:1) and Pt–Pd/C (3:1) catalysts. Chronoamperometry experiments and tests in direct ethanol fuel cells of the as-prepared catalysts shows that the activity for ethanol oxidation of (PtSn) alloy /SnO 2 is higher than that of (PtSnPd) alloy /SnO 2 . This result, obtained with the same Pt/SnO 2 atomic ratio in all the samples, indicates the critical role of the alloy phase characteristics of these catalysts on their activity for ethanol oxidation.

The performance and durability of low-temperature fuel cells seriously depend on catalyst support materials. Catalysts supported on high surface area carbons are widely used in low temperature fuel cells. However, the corrosion of carbonaceous catalyst-support materials such as carbon black has been recognized as one of the causes of performance degradation of low-temperature fuel cells, in particular under repeated start-stop cycles or high-potential conditions. To improve the stability of the carbon support, materials with a higher graphitic character such as carbon nanotubes and carbon nanofibers have been tested in fuel cell conditions. These nanostructured carbons show a several-fold lower intrinsic corrosion rate, however, do not prevent carbon oxidation, but rather simply decrease the rate. Due their high stability in fuel cell environment, ceramic materials (oxides and carbides) have been investigated as carbon-substitute supports for fuel cell catalysts. Moreover, the higher specific electrocatalytic activity of some ceramic supported metals than unsupported and carbon supported ones, suggests the possibility of a synergistic effect by supporting metal catalyst on ceramic supports. This paper presents an overview of ceramic materials tested as a support for fuel cell catalysts, with particular attention addressed to the electrochemical activity and stability of the supported catalysts.

To increase their electrochemically active surface area, catalysts supported on high surface area materials, commonly carbons, are widely used in low-temperature fuel cells. Recent studies have revealed that the physical properties of the carbon support can greatly affect the electrochemical properties of the fuel cell catalyst. It has been reported that carbon materials with both high surface area and good crystallinity can not only provide a high dispersion of Pt nanoparticles, but also facilitate electron transfer, resulting in better device performance. On this basis, novel non-conventional carbon materials have attracted much interest as electrocatalyst support because of their good electrical and mechanical properties and their versatility in pore size and pore distribution tailoring. These materials present a different morphology than carbon blacks both at the nanoscopic level in terms of their pore texture (for example mesopore carbon) and at the macroscopic level in terms of their form (for example microsphere). The examples are supports produced from ordered mesoporous carbons, carbon aerogels, carbon nanotubes, carbon nanohorns, carbon nanocoils and carbon nanofibers. The challenge is to develop carbon supports with high surface area, good electrical conductivity, suitable porosity to allow good reactant flux, and high stability in fuel cell environment, utilizing synthesis methods simple and not too expensive. This paper presents an overview of carbon supports for Pt-based catalysts, with particular attention on new carbon materials. The effect of substrate characteristics on catalyst properties, as electrocatalytic activity and stability in fuel cell environment, is discussed.

Carbon supported ternary Pt–Sn–Rh (1:1:0.3 and 1:1:1) alloy catalysts were synthesized by reduction of the metal precursors with formic acid and characterized by EDX, XRD and TEM analyses. Their activity for ethanol oxidation was compared with that of binary Pt–Sn/C and Pt–Rh/C prepared with the same method. XRD analysis indicated that both the lattice parameter and the crystallite size of the Pt–Sn–Rh alloy catalysts are higher than those of Pt–Rh/C and lower than those of Pt–Sn/C. The intermediate value of the particle size of the ternary alloy catalysts was confirmed by TEM images. Linear sweep voltammetry measurements indicated that, for potentials higher than 0.45 V versus RHE, the ternary Pt–Sn–Rh alloy catalysts possess the higher activity for ethanol electro-oxidation, while for potentials lower than 0.45 V versus RHE the electrochemical activity of the ternary catalysts was lower than that of the binary Pt–Sn catalyst. The enhanced activity for ethanol electro-oxidation on the ternary Pt–Sn–Rh catalysts was ascribed to the formation of a ternary alloy and to the lower particle size.

A carbon supported Pt–Sn electrocatalyst in the Pt/Sn atomic ratio 50:50 was prepared by the reduction of Pt and Sn precursors with formic acid and thermally treated at 200 °C (i.e., in the presence of solid tin) and 500 °C (in the presence of molten tin) in flowing hydrogen. In the absence of thermal treatment, X-ray diffraction (XRD) analysis showed a solid solution of Sn in the face centered cubic (fcc) Pt and SnO2. After thermal treatment, the formation of a main phase of hexagonal PtSn (niggliite) and a secondary phase of cubic Pt3Sn was observed in the Pt50Sn50 catalyst. The relative amount of the PtSn phase increased with increasing thermal treatment temperature. The presence of molten tin gave rise to the formation of some big particles during annealing at 500 °C. The activity for the ethanol oxidation reaction (EOR) of the as-prepared catalyst was higher than that of both thermally treated catalysts and Pt75Sn25/C and Pt50Ru50/C by E-TEK. The higher activity for the EOR of the as-prepared Pt–Sn catalysts was ascribed to the presence of a large amount of SnO2.

The development of high performance electrode materials is currently one of the main activities in the field of the low temperature fuel cells, fuelled with H 2 /CO or low molecular weight alcohols. A promising way to attain higher catalytic performance is to add a third element to the best binary catalysts actually used as anode and cathode materials. In Part I of this review an overview of the preparation and structural characteristics of Pt-based ternary catalysts was presented. This part of the review deals with the electrochemical properties of these catalysts regarding their CO tolerance and electrocatalytic activity for methanol and ethanol oxidation in the case of anode materials, and their activity for oxygen reduction and stability in fuel cell conditions when used as cathode materials.

Carbon supported Pt alloyed with first row transition elements (Pt–M/C) is being used as improved cathode catalyst for low temperature fuel cells. These catalysts have been usually prepared by deposition of the non-precious metal onto pre-formed carbon supported platinum, followed by alloying at temperatures of the order or above 700 °C. As the thermal treatment at high temperature gives rise to an undesired metal particle growth, synthetic methods based on the simultaneous deposition of Pt and M on the carbon substrate, followed by thermal treatment at lower temperature have been developed. In this paper the formation of Pt–M/C by low/intermediate temperature methods is reviewed. Moreover, to investigate the effect of the conditions used in the synthesis on the Pt:M atomic ratio, the degree of alloying and the particle size, carbon supported Pt–Co electrocatalysts with nominal Pt:Co atomic ratio 75:25 were prepared by a low temperature chemical reduction of the precursors with sodium borohydride at two different temperatures and NaBH 4 concentrations. The physical characterization of these electrocatalysts was performed by energy dispersive X-ray analysis and X-ray diffraction.

Carbon supported Pt-Sn alloy catalysts were prepared by reduction of Pt and Sn precursors with formic acid and characterised by X-ray diffraction, high resolution transmission electron microscopy and X-ray absorption near- edge structure analyses. Their electrocatalytic activity for ethanol oxidation was compared with commercial Pt/C and Pt3Sn/C electrocatalysts. The synthetized PtSn catalysts presented a low degree of alloy formation and high contents of Sn oxides. The electrocatalytic activity for ethanol oxidation in linear sweep voltammetry experiments at room temperature is greatly enhanced, mainly at low potentials, on Pt3Sn and Pt2Sn catalysts prepared by reduction with formic acid, while only a slight improvement is observed on Pt9Sn prepared with formic acid. On the other hand, a commercial Pt3Sn catalyst with a high degree of alloying showed the highest current performance as anode material in a direct ethanol fuel cell (DEFC) operating at 90 and 110 oC.

Carbon supported platinum metal alloy catalysts (Pt–M/C) are widely used in low temperature fuel cells. Pt alloyed with first-row transition elements is used as improved cathode material for low temperature fuel cells. A major challenge for the application of Pt–transition metal alloys in phosphoric acid (PAFC) and polymer electrolyte membrane (PEMFC) fuel cells is to improve the stability of these binary catalysts. Dissolution of the non-precious metal in the acid environment can give rise to a decrease of the activity of the catalysts and to a worsening of cell performance. The purpose of this paper is to provide a better insight into the stability of these Pt–M alloy catalysts in the PAFC and PEMFC environments and the effect of the dissolution of the non-precious metal on the electrocatalytic activity of these materials, in the light of the latest advances on this field. Additionally, the durability of a PtCo/C cathode catalyst was evaluated by a short test in a single PEM fuel cell.

The formation, structure and transport properties of LiCoO 2 are described. LiCoO 2 exhibits two crystal structures, depending on both the preparation method and synthesis temperature. High temperature lithium cobalt oxide (HT-LiCoO 2 ) has a hexagonal layered structure, while the low temperature oxide (LT-LiCoO 2 ) has a cubic spinel-related structure. The dependence of the morphological characteristics (grain size, size distribution, crystallinity) of LiCoO 2 on synthesis method as well as their effect on the electrochemical properties are extensively reviewed. As the electrochemical properties and the electrical conductivity strongly depend on the structure of the oxide, primary attention is given to lithium cobalt oxide with defect structure and lithium and oxygen nonstoichiometry.

The formation, structure and transport properties of LixNi1−xO solid solutions with x≤0.3 are described. Pure stoichiometric nickel oxide is a green insulator compound with rocksalt structure. When Li+ partially substitute the normal sites of Ni2+, a hole is introduced in the form of Ni3+ or O− to keep charge neutrality conditions, and the oxide becomes a black semiconductor. For Li atomic fraction x>0.3 a rhombohedral distortion of the cubic structure by partial lithium and nickel ions ordering on alternate 〈1 1 1〉 planes takes place, giving rise to a hexagonal structure. Some questions, regarding the hole state, the ordering and vacancy presence in the solid solutions, are discussed. The effect of Li content in the solid solutions on the most typical charge-and-mass transport properties, as electrical conductivity, thermoelectric power and chemical diffusivity, is reviewed.

Platinum metal alloys are widely used in low temperature fuel cells. Carbon-supported PtRu alloys are generally used as catalyst in direct methanol fuel cell (DMFC) anodes and as CO tolerant catalyst in solid polymeric fuel cell (PEFC) anodes. Pt alloyed with first-row transition elements is used as improved catalyst for both PEFC and DMFC cathodes. This paper presents an overview of the preparation and chemical and morphological characteristics of carbon-supported PtM (M=metal) catalysts.

Supported platinum electrocatalysts are generally used in low temperature fuel cells to enhance the rates of the hydrogen oxidation and oxygen reduction reactions. In such catalysts, the high surface to volume ratios of the platinum particles maximize the area of the surfaces available for reaction. It is the structure and proper dispersal of these platinum particles that make low-loading catalysts feasible for fuel cell operation, lowering the cost of the system. If the platinum particles cannot maintain their structure over the lifetime of the fuel cell, change in the morphology of the catalyst layer from the initial state will result in a loss of electrochemical activity. This loss of activity in the platinum/carbon catalysts due to the agglomeration of platinum particles is considered to be a major cause of the decrease in cell performance, especially in the case of the cathode. In the light of the latest advances on this field, this paper reviews the preparation methods of these catalysts, their microstructural characteristic and their effect on both thermal and in cell conditions stability.

The formation mechanism of Pt/C catalysts using non-oxidized active carbon support and the weak reducing agent Na2S2O4 was investigated. Platinum on carbon catalysts were fabricated by an impregnation/reduction process of the Pt-precursor H2PtCl6 on carbon support. The effect of thermal treatment in argon up to 700°C on the structural characteristics of these catalysts was studied by XRD and TEM analyses. The importance of carbon support properties on Pt/C formation was recognized. Before thermal treatment a very weak internal organization (a very small particle size and amorphous structure) in the metal was obtained. Thermal treatment at relatively low temperatures leads to the growth and then to the crystallization of platinum particles in the well-known face centered cubic structure. The sintering of Pt particles occurs through the migration of Pt atoms on the carbon support, likely by a bridge-bonding mechanism on sulfur atoms. A fast growth of Pt particles occurred in the temperature range 300—400°C. Thermal crystallization, instead, occurred mostly going from 400 to 550°C. Following annealing at 550°C, the formation of platinum sulfide was revealed. The sample thermally treated at 700°C showed an anomalous XRD pattern with Pt reflexions shifted towards high angles and an increase of Pt[111]/Pt[220] peak intensity ratio.

The effect of the thermal treatment at 1000°C in air of Li/Ni/MgO system was investigated by X-ray diffraction (XRD) analysis. During air calcinations of Li/Ni/MgO system, the formation of a ternary Li y Ni x Mg 1− y − x O solid solution takes place. The presence of Ni 3+ ions, as charge-compensating species, allows the incorporation of a high amount of Li + ions into MgO lattice without the formation of oxygen vacancies.

Lithium loss from LiCoO 2 following isochronal thermal treatment for 5 h in the temperature range 850–1300°C was determined by thermogravimetric (TGA) and diffractometric (XRD) measurements. Lithium vaporization starts from 900°C, and following thermal treatment at 1300°C 85% of lithium was lost. At 1050°C a change in the mechanism of lithium and oxygen evaporation was observed. Initially, following lithium loss, Li y Co 2− y O 2 (solid solution of CoO in LiCoO 2 ) was formed. An activation energy of 305 kJ mol −1 , not too far from the heat of reaction from Li 2 O to Li 2 O 2 vapour, was obtained. Phase transition to cubic Li 0.065 Co 0.935 O structure occurred starting from thermal treatment at 1050°C. Both hexagonal and cubic lithium cobalt oxide structures were subjected to phase transition to get LiCoO 2 and Co 3 O 4 during cooling, but the cubic phase was stabilized against phase transition with increasing temperature.

Carbon supported PtRu alloys were prepared by impregnation of Pt and Ru precursors on a porous carbon support, followed by reduction of the metals with Na2S2O4. After reduction, the samples were thermal treated in argon up to 700°C. The samples were characterized by atomic absorption (AAS) and X-ray diffraction (XRD) measurements. Before thermal treatment only carbon reflexions were visible in XRD pattern. The reflexions of face centered cubic (f.c.c.) PtRu alloy were revealed in XRD pattern starting from thermal treatment at 300°C. No hexagonal close packed (h.c.p.) RuPt reflexions were detected. During thermal treatment, part of Ru reacted with sulphur forming RuS2. Ru content in the alloy increased with increasing thermal treatment temperature. The results indicated that, first, f.c.c. Pt with few Ru alloyed was formed, then, with increasing thermal treatment temperature, part of Ru atoms present in the sample in an amorphous form entered in the crystal structure of the platinum by a diffusion-controlled mechanism. Also after thermal treatment at high temperatures there was a large part of unalloyed Ru, with only about 49% of the Ru alloyed with the Pt. PtRu particle size was in the range 15–20 nm.

Lithium loss from Li x Co 1− x O solid solutions at 1200°C was investigated by diffractometric (XRD) and gravimetric measurements. The results of XRD analysis indicated that the time dependence of Li 2 O evaporation from the solid solutions was 0.2 for a nominal Li 10% sample, while for a nominal Li 20% sample, the time dependence changed from 1 to 0.2 following 5 h of isothermal treatment. This dimensionless parameter is related to the evaporation mechanism. The behaviour of the nominal Li 20% sample was related to the presence of layered Li y Co 2− y O 2 solid solution in the external part of the particles. Lithium content of the solid solution attained a constant value of 0.06, independent of nominal lithium content of the sample. Then, the solid solution with x about 0.06 seems to be stable against lithium loss. Experimental weight loss, due to both lithium loss and Li x Co 1− x O stabilization against phase transition, was compared with calculated weight loss using the parameters obtained from XRD analysis.

Ni, NiO and LixNi1-xO are the cathodic materials commonly used in molten carbonate fuel cells (MCFCs). Since the instability of the cathode is recognized as a major hindrance to MCFC development, in this report the behaviour of these nickel species in molten alkali carbonates is reviewed, analyzing step by step the processes of lithiation, dissolution and sinterization at cell operating temperatures.

The effect of polytetrafluoroethylene (PTFE) content on morphological characteristics of carbon/PTFE films deposited on porous carbon support was investigated by mercury-porosimetry, scanning electron microscopy (SEM) and a.c. impedance spectroscopy. The microstructure of the film was affected by the content of fluoropolymer. The layer has two distinctive pore distributions with a boundary of about 0.35 μm. The polymer coated the pores with size higher than 1 μm (carbon interagglomerate pores), while the pores with size lower than 1 μm were not influenced by the presence of PTFE. Above 40 wt% PTFE, a further supply of polymer did not fill the pores, but increased the thickness of the sample. The presence of cracks, increasing in number and size with PTFE content, was also revealed. © 1998 Chapman & Hall

Liquid phase sintering of Li x Ni 1 − x O solid solutions with x = 0.30 and 0.44, obtained by the reaction of a nickel and lithium carbonate powder mixture, was evaluated by means of the shrinkage of the specimens. Only when part of the Li x Ni 1 − x O crystalline structure was present as the hexagonal phase, the presence of a reactive liquid phase of undecomposed lithium carbonate promoted the sintering process.

Lithium cobalt oxide compounds are promising materials in various industrial applications, as water electrolysis cells, rechargeable lithium batteries, molten carbonate fuel cells and humidity ceramic sensors. This paper presents an overview of the preparation and properties of LiCoO compounds: lithiated Co 3 O 4 , LiCoO 2 and LiCoO 2 CoO solid solutions.

The historical development and current status of gas diffusion electrodes for polymer electrolyte fuel cells ( PEFCs) are presented. Two and three-layer electrodes are compared. The effects of both the characteristics and the amount of the materials composing the electrode on the cell performance are presented. These include: the characteristics of the porous substrate; the wettability of the diffusion layeer; the characteristics of the catalyst, which is commonly platinum supported on carbon (Pt loading, Pt particle size, Pt/C ratio, Pt deposition method); the presence of perfluorosulfonate ionomer; and the way that the catalytic layer is filled. Attention is also given to the fabrication process of the electrodes and thermal treatments.

The mechanism of formation of lithium nickel oxide phases by solid state reaction of Ni and Li 2 CO 3 in the temperature range 700–800 °C was investigated. Cubic Li x Ni 1 − x O solid solution with nominal composition x = 0.30 was obtained throug the formation of hexagonal Li x Ni 1 − x O. However, hexagonal Li x Ni 1 − x O with x = 0.44 arose from cubic Li x Ni 1 − x O. To explain this behaviour, the existence of an equilibrium relationship between cubic disordered and hexagonal ordered Li x Ni 1 − x O phases is proposed.

The casting behaviour, ultimate tensile strength and the sintering process of tapes consisting of nickel powder, ethanol, po!yvinylbutyral as the binder, polyethylene glycol (molecular weight 200, PEG2) or dibutyl phthalate (DBP) as the plasticizer, and glycerol trioleate as the dispersant agent, were studied. On increasing powder content in the slurry the packing factor of nickel in the green increased, but the ultimate tensile stress and strain to failure decreased. Increasing binder to total binder ratio caused the green density and strain to failure to decrease, but the ultimate tensile stress increased for both PEG2 and DBP. The maximum strain to failure (about 35% for both PEG2 and DBP) in the case of DBP was obtained with an amount of plasticizer lower than that of PEG2. When tapes having different composition were sintered at various temperatures, a linear relation was found between packing factor and fired density, independently of the kind of binder and plasticizer used.

The phase evolution and the sintering process of Co/Li2CO3 mixtures following thermal treatment at 1200 °C in air were evaluated. In the dynamic step of the thermal treatment, Co3O4 and LiCoO2 were obtained and the densification and grain size of lithiated samples were higher than those of pure Co. In the isothermal step at 1200 °C, decomposition of LiCoO2 and diffusion of lithium ions into CoO with formation of LixCo1 − xO solid solution were denoted, and after 40 h of isothermal treatment almost all LiCoO2 decomposed. The sintering constant n varied from 0.27 to 0.37, which suggested that grain-boundary diffusion was the primary mechanism for material transport. For all the compositions considerable morphological changes took place during thermal treatment.

Co and Li{sub 2}CO{sub 3} were used as starting materials to obtain cobalt-based plaques of potential use in molten carbonate fuel cell technology. Samples were prepared by thermal treatments in the temperature range 800-1300{degrees}C. Their composition and microstructure have been investigated at room temperature by X-ray diffraction analysis (Rietveld refinement), weight change and density data, porosimetry, and scanning electron microscopy. It is shown that a highly nonstoichiometric Co{sub 3}O{sub 4} forms on lithium-containing samples in the entire temperature range investigated, while a stoichiometric Co{sub 3}O{sub 4} is always obtained in the absence of Li. Moreover, clear evidence has been obtained that sinterization starts at lower temperatures on lithiated samples than on pure Co ones and that it causes the formation of consistent amounts of stoichiometric CoO in both types of sample. It is argued that the increased sinterization rate shown by Li-containing samples is due to the highly defective structure of their Co{sub 3}O{sub 4} phase.

The effect of the relationship between particle size (d), inter-particle distance (x i ), and metal loading (y) of carbon supported fuel cell Pt or PtRu catalysts on their catalytic activity, based on the optimum d (2.5–3 nm) and x i /d (>5) values, was evaluated. It was found that for y