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The advantages of the use of glucose as a fuel in low-temperature fuel cells are its abundance, easy availability, low cost, non-toxicity and no storage problems. Renewable biomass resources, including starch and cellulose, can be readily converted to the glucose molecule with little energy cost. This overview is focused on abiotic external glucose fuel cells (GFCs), presenting an appreciable performance (maximum power density ≥ 0.1 mW cm−2). Various types of traditional acid and alkaline fuel cells, using solid catalysts, have been fueled with glucose. A comparison of traditional fuel cells fueled with low molecular weight compounds and glucose showed that GFCs have a considerably lower performance, due to partial glucose oxidation, with formation of gluconic acid, by releasing only two electrons, so there is still much room for their improvement. A new type of fuel cells, using liquid catalysts instead of solid catalysts, have recently aroused great interest. When used as a fuel in liquid catalyst fuel cells (LCFCs), glucose provides better cell performance than more simple fuels. In LCFCs glucose can be more deeply oxidized, up to CO2. The hydroxyl/carbon number of polyhydric alcohols seems to be the key factor that determines the LCFC performance, indicating that higher polyhydric compounds, such as glucose, are more suitable fuels for LCFCs than simple alcohols.

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.

The conversion of methane into chemicals is of interest to achieve a decarbonized future. Fuel cells are electrochemical devices commonly used to obtain electrical energy, but can be utilized either for chemicals production or both energy and chemicals cogeneration. In this work, the partial oxidation of methane in fuel cells for electricity generation and valuable chemicals production at the same time is reviewed. For this purpose, different types of methane-fed fuel cells, both low temperature fuel cells, such as PEMFCs and AAEMFCs, and high temperature fuel cells, such as SOFCs, have been used. Also if few works have been devoted to this topic, the promising results drive the development of fuel cells using methane as the source for the cogeneration of power and valuable chemicals.

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/CeO2/C electrocatalysts in different compositions were prepared and their structural characteristics and activities for ethanol oxidation in alkaline media were evaluated. In the presence of CeO2, an increase in the platinum particle size was observed. XANES measurements indicated that the Pt d-band vacancies increased with increasing CeO2 amounts. For the first time, the decrease in electro activity was described to an electronic effect for high CeO2 contents. The dependence of the activity for ethanol oxidation on CeO2 content went to a maximum, due to the counteracting bifunctional and electronic effects of the metal oxide.

Made available in DSpace on 2021-06-25T10:17:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-04-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) The glycerol oxidation reaction (GLYOR) was evaluated using an Au/C electrocatalyst under alkaline conditions and varying glycerol (GLY) concentration. This electrocatalyst was synthesized by the borohydride reduction method. Au/C was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical techniques associated with in situ attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR). XRD diffractograms showed the presence of Au (fcc). Cyclic voltammetry assisted by ATR-FTIR in situ measurements revealed that GLY oxidation on gold leads to the formation of a high amount of glyceraldehyde (GLYAD) for low GLY concentrations, while a lower amount of GLYAD was observed and the formation of dihydroxyacetone (DHA) was prevalent for high GLY concentrations. For high GLY concentrations DHA is almost stable, whereas for low GLY concentration DHA is fast oxidized to hydroxypyruvate. The excellent GLYOR activity of the Au/C catalyst in low GLY concentrations leads to the formation of deeper oxidized C1 species. Instituto de Pesquisas Energéticas e Nucleares IPEN/CNEN-SP, Av. Prof. Lineu Prestes, 2242 Cidade Universitária Biosciences Institute São Paulo State University - UNESP Coastal Campus Scuola di Scienza dei Materiali, Via 25 aprile 22, Cogoleto Biosciences Institute São Paulo State University - UNESP Coastal Campus FAPESP: 2014/09087-4 FAPESP: 2014/50279-4 FAPESP: 2017/11937-4 CNPq: 300816/2016-2 CAPES: 88882.315566/2019

In recent years the use of renewable sources, such as lignocellulosic biomass (LCB), as the fuel for various types of fuel cells received growing interest. Different types of fuel cells, that is, operated at low temperatures (T

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 conversion of methane into chemicals is of interest to achieve a decarbonized future. Fuel cells are electrochemical devices commonly used to obtain electrical energy but can be utilized either for chemicals’ production or both energy and chemicals cogeneration. In this work, the partial oxidation of methane in fuel cells for electricity generation and valuable chemicals production at the same time is reviewed. For this purpose, we compile different types of methane-fed fuel cells, both low- and high-temperature fuel cells. Despite the fact that few studies have been conducted on this subject, promising results are driving the development of fuel cells that use methane as a fuel source for the cogeneration of power and valuable chemicals.

Binary and ternary Pt75CoxNi25-x/C (x = 0, 0.9, 12.5, 24.1, and 25) electrocatalysts were prepared by a polyol method, and their activity for carbon monoxide and glycerol oxidation in alkaline media was compared to that of a conventional Pt/C catalyst. Formation of partially alloyed catalysts was detected by XRD analysis, with the most part of the non-precious metals in a non-alloyed form. The onset potential for carbon monoxide and glycerol oxidation on binary and ternary Pt75CoxNi25-x/C catalysts was lower than that on Pt/C. The higher activity for glycerol oxidation of the Pt75Co0.9Ni24.1/C and Pt75Co12.5Ni12.5/C catalysts than that of the parent binary catalysts was ascribed to the formation of highly active CoxNi1-x(OH)2/CoxNi1-xOOH redox couples with a Co/Ni atomic ratio ≤ 1. Conversely, the replacement of a small amount of Co (0.9 at.%) by Ni did not increase the glycerol oxidation activity of the resulting Pt75Co24.1Ni0.9/C catalyst. The higher activity for glycerol oxidation of Pt75Co12.5Ni12.5/C than that of Pt75Co0.9Ni24.1/C for potentials > 0.7 V vs. RHE, despite the lower Ni-based oxide content and the higher particle size, indicated that at these potentials, the Co12.5Ni12.5(OH)2/Co12.5Ni12.5OOH redox couple is more active for glycerol oxidation than the Co0.9Ni24.1/Co0.9Ni24.1OOH redox couple.

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.

In this work we prepared binary Pt-based electrocatalysts supported on carbon with a 80:20 (Pt:M) atomic ratio (where M = Rh, Pd and Ni) and tested their activity for the ethylene glycol oxidation reaction (EGOR) in alkaline media. Pt90Pd10/C showed the highest catalytic activity for the EGOR. Then, to estimate the optimum Pd content for the EGOR, a new series of PtPd catalysts within a wide range of compositions was synthesized and tested. The electroactivity is dependent on the composition of PtPd and reaches a maximum at 32 at.% Palladium. In situ FTIR results suggest the presence of Pd increases the production of glycolate, while hinders the formation of carbonate. This inhibition, in turn, seems to be dependent on a previous scission of the molecules. Hence, compositions richer in Pd are more tolerant to surface poisoning because the production of fragments possessing a single carbon atom (such as CO) is hindered over these surfaces.

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.

Ternary Pt–Sn–Ce/C catalysts were prepared by a modified formic acid method, and their activity for the ethanol oxidation reaction (EOR) was compared to that of Pt–Sn/C, Pt–Ce/C and Pt/C catalysts. No bulk alloy formation was detected by XRD analysis. XPS measurements indicated no segregation on the catalyst surface and the presence of Sn(0) and SnO x , Ce 2 O 3 and CeO 2 oxides. The onset potential for CH 3 CH 2 OH oxidation on Pt–Sn/C and Pt–Sn–Ce/C (60:20:20) catalysts, which have the highest Sn content on the surface, was lower than that of Pt–Sn–Ce/C (70:20:10) and (50:20:30), Pt–Ce/C and Pt/C catalysts. This work highlights the dependence on the potential of the effect of cerium in Pt–Sn–Ce/C catalysts on the EOR activity and on the reaction mechanism. By derivative voltammograms, different reaction pathways at different potentials, involving Sn (at ca. 0.44 V vs. RHE), Sn + Ce (at ca. 0.55 V vs. RHE) and Ce (at ca. 0.67 V vs. RHE) were inferred. The Pt–Sn–Ce/C catalysts were less tolerant to poisoning by ethanol oxidation intermediate species than Pt/C and Pt–Sn/C, but more stable than Pt–Ce/C catalysts. DEFC tests at 90 °C indicated that a higher Sn surface content is more effective for ethanol oxidation than the addition of Ce to Pt–Sn/C.

Ternary Pt–Sn–Pr/C (70:10:20), (70:15:15) and (45:45:10) electro-catalysts were prepared by a modified formic acid method, and their activity for the ethanol oxidation reaction (EOR) was compared with that of Pt–Pr/C catalysts prepared by the same methods and that of commercial Pt–Sn/C (75:25) and Pt/C catalysts. Among all the catalysts, the Pt–Sn–Pr/C (45:45:10) catalyst presented both the highest mass activity and the highest specific activity. The steady state electrochemical stability of ternary Pt–Sn–Pr catalysts increased with the surface Sn/Pt atomic ratio. Following repetitive potential cycling (RPC), the activity for ethanol oxidation of Pt–Sn–Pr/C catalysts with high surface Sn/Pt atomic ratio was considerably higher than that of the corresponding as-prepared catalysts, and increased with increasing the Sn/Pt ratio. The increase of the EOR mass activity following RPC was ascribed to the increase of either the specific activity (for the Pt–Sn–Pr/C (70:15:15) catalyst) or the electrochemically active surface area (for the Pt–Sn–Pr/C (45:45:10) catalyst). Dissolution of Sn and Pr oxides from Pt–Sn–Pr/C catalyst surface was observed following RPC.

In view of a possible use as anode materials in acidic direct alcohol fuel cells, the electro-catalytic activity of Pt-Ni and Pt-M-Ni (M = Ru, Sn) catalysts for methanol and ethanol oxidation has been widely investigated. An overview of literature data regarding the effect of the addition of Ni to Pt and Pt-M on the methanol and ethanol oxidation activity in acid environment of the resulting binary and ternary Ni-containing Pt-based catalysts is presented, highlighting the effect of alloyed and non-alloyed nickel on the catalytic activity of these materials.

Ternary Pt-Sn-Rh/C catalysts of Pt:Sn:Rh = 1:0.8:0.2 and 1:1:0.33 atomic ratios were synthesized using the formic acid method and their electrochemical activities were compared for ethanol oxidation with that of binary Pt-Sn/C (1:1) and Pt-Rh/C (1:0.11) catalysts. XRD analysis indicated the presence of Sn in both alloyed and oxide form and suggested the formation of a ternary Pt-Sn-Rh alloy in both catalysts. The particle size by TEM was around 3.5 nm for all catalysts. The efficiency for Pt utilization increased with Rh content. Pt-Sn-Rh/C catalysts exhibited higher catalytic activity for ethanol oxidation than Pt-Rh/C, but lower than Pt-Sn/C. Among ternary catalysts, Pt-Sn-Rh/C (1:0.8:0.2) was the most active. I n situ IRRAS showed Rh plays a dual counteracting role during ethanol electro-oxidation on Pt-Sn-Rh/C catalysts, once it promotes C-C bond breaking, thus favouring CO 2 formation, but hinders adsorption of ethanol, decreasing the production of acetic acid.

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.

Among noble metal electrocatalysts, only iridium presents high activity for both the oxygen reduction reaction (ORR) in acid medium, in the oxide form, and the oxygen evolution reaction (OER) in acid medium, alloyed with first row transition metals. Indeed, platinum, the best catalyst for the ORR, has poor activity for the OER in any form, and ruthenium, the best catalyst for the OER, in the oxide form, possess poor activity for the ORR in any form. In this work, an overview of the application of Ir and Ir-containing catalysts for the OER in proton-exchange membrane water electrolyzer anodes, for the ORR in proton exchange membrane fuel cell cathodes, and for both OER and ORR in unit regenerative fuel cell oxygen electrodes is presented.

Pt–Pr/C electrocatalysts were prepared by a modified formic acid method, and their activity for carbon monoxide and ethanol oxidation, their short term stability and durability were compared to that of commercial Pt/C and Pt–Sn/C (3:1) catalysts. By derivative voltammetry (DV) it was found that ethanol electro-oxidation takes place by two main pathways at different potentials. It was observed that, in the presence of Pr, ethanol electro-oxidation takes place mostly through the pathway at lower potential, which is the most interesting for fuel cell application. The Pt–Pr/C catalysts were less tolerant to poisoning by ethanol oxidation intermediate species than Pt/C. Durability test by a repetitive potential cycling under Ar atmosphere revealed a good structural stability of Pt–Pr/C catalysts. A repetitive potential cycling under CO atmosphere carried out on the Pt–Pr/C (1:1) catalyst, instead, indicated a structural change, likely by formation of a core–shell structure.

Combinatorial chemistry and high-throughput screening represent an innovative and rapid tool to prepare and evaluate a large number of new materials, saving time and expense for research and development. Considering that the activity and selectivity of catalysts depend on complex kinetic phenomena, making their development largely empirical in practice, they are prime candidates for combinatorial discovery and optimization. This review presents an overview of recent results of combinatorial screening of low-temperature fuel cell electrocatalysts for methanol oxidation. Optimum catalyst compositions obtained by combinatorial screening were compared with those of bulk catalysts, and the effect of the library geometry on the screening of catalyst composition is highlighted.

The low price, highly active triol structure, high volumetric energy density, simple storage and environment-friendly properties make glycerol a promising fuel for an alkaline direct alcohol fuel cell (ADAFC). Unlike other ADAFCs, alkaline direct glycerol fuel cells (ADGFCs) can be used either to generate only energy (the common use of fuel cells) or to produce both energy and valuable chemicals. This work presents an overview of catalysts for glycerol oxidation in alkaline media, and their use in ADGFCs. A particular attention was paid to binary and ternary catalysts able both to increase the selectivity to valuable C3 glycerol oxidation products, reducing the C–C bond cleavage, and simultaneously to enhance glycerol conversion.

The effect of chelating agents (citrate and EDTA) on the visible light photocatalytic activity of natural pyrite for the inactivation of Escherichia coli ATCC 25922 (E. coli) was investigated. The influence of various parameters, such as chelating agent and H2O2 concentration, light intensity and aeration rate, was evaluated experimentally and through kinetic models. The presence of a chelating agent enhanced the photocatalytic activity of natural pyrite, and citrate was more effective than EDTA, considerably improving bacteria inactivation in natural pH and reducing the drawbacks of the photocatalytic inactivation system. For both citrate-pyrite and EDTA-pyrite, the inactivation rate went through a maximum for a concentration of the chelating agent of 0.5 mM. The increase of the light intensity (10–60 mW cm−2), H2O2 concentration (10–25 mg L-1) and aeration rate (2-8 L min-1) improved the radical generation, resulting in a high inactivation effect. The low effect of H2O2 on the catalytic activity of pyrite in the presence of EDTA was likely due to the inhibition of the hydrogen peroxide-to-hydroxyl radical conversion by EDTA. On the other hand, degradation of citrate at high aeration rate occurred, decreasing the catalytic activity of the citrate-pyrite system. Scavenging tests indicated that the bulk hydroxyl radicals are the most reactive radical species in the bacterial inactivation, closely followed by valence band holes, while conduction band electrons play a less important role. In addition, in order to generate predictions and to better understand the process, artificial neural networks were used as models for the considered process: the obtained performance indexes indicated a good correlation between experimental and predicted values.

Pt2RuMo/C catalysts were synthesized by the modified polyol method in the presence and absence of Li(C2H5)3BH (LBH), annealed at 600 &deg, C under H2 atmosphere to improve the reduction of Pt and Ru to provide stronger interactions between Mo and another metals. LBH affected the physico-chemical characteristics of Pt2RuMo, that is, in the presence of LBH an increment of Mo(IV) amount and a decrease in the PtRu alloying degree were observed. The catalytic activity for hydrogen oxidation in the presence and absence of CO (CO tolerance) of the Pt2RuMo/C catalysts as anodes in polymer electrolyte membrane fuel cells (PEMFCs) was compared to that of a commercial PtRu/C catalyst. The results indicated that the CO tolerance increased with an increase in Mo(IV) content, but the stability increased with an increment of the amount of Ru oxides in the catalysts.

In view of their possible use as anode materials in acid direct ethanol fuel cells, the electrocatalytic activity of Pt-Ru and Pt-Ru-M catalysts for ethanol oxidation has been investigated. This minireview examines the effects of the structural characteristics of Pt-Ru, such as the degree of alloying and Ru oxidation state, on the electrocatalytic activity for ethanol oxidation.

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.

The effect of alloying degree on the ethanol oxidation activity of a PtRu/C catalyst with a Pt/Ru atomic ratio of 1:1 was investigated by measurements in a half-cell and in a single direct ethanol fuel cell. The increase of the amount of Ru alloyed from one third to two thirds of the total Ru content in the catalyst clearly resulted in a decrease of the ethanol oxidation activity. As the amount of the highly active hydrous ruthenium oxide was near the same, the lower activity of the PtRu/C catalyst with higher alloying degree was mainly ascribed to the presence of an excessive number of Ru atoms around Pt active sites, hindering ethanol adsorption on Pt sites. The reduced ethanol adsorption could be also related to the decreased Pt–Pt bond distance and to the electronic effects by alloying.

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.

The electrocatalytic activity for CO, H2/CO and CH3OH oxidation of Pt-Sn catalysts has been extensively investigated for a possible use as anode materials for low-temperature fuel cells. This paper presents an overview of the relationship between the structural characteristics of the catalysts (catalyst composition, degree of alloying, presence of oxides) and their electrocatalytic activity for the oxidation of the different fuels.

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.

The faster kinetics of the alcohol oxidation and oxygen reduction reactions in alkaline direct alcohol fuel cells (ADAFCs), opening up the possibility of using less expensive metal catalysts, as silver, nickel and palladium, makes the alkaline direct alcohol fuel cell a potentially low cost technology compared to acid direct alcohol fuel cell technology, which employs platinum catalysts. A boost in the research regarding alkaline fuel cells, fuelled with hydrogen or alcohols, was due to the development of alkaline anion-exchange membranes, which allows the overcoming of the problem of the progressive carbonation of the alkaline electrolyte. This paper presents an overview of catalysts and membranes for ADAFCs, and of testing of ADAFCs, fuelled with methanol, ethanol and ethylene glycol, formed by these materials.

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.

Due to their high accessible surface area, low resistance and high stability, conducting polymers have been investigated as carbon-substitute supports for fuel cell catalysts. The main reason for incorporating metallic particles into porous polymeric matrixes is to increase the specific area of these materials and thereby improve the catalytic efficiency. Polymer-supported metal particles also present higher tolerance to poisoning due to the adsorption of CO species, in comparison to the serious problem of poisoning of bulk and carbon-supported metals. Moreover, conducting polymers are not only electron conducting, but also proton conducting materials, so they can replace Nafion in the catalyst layer of fuel cell electrodes and provide enhanced performance. This paper provides a review of the state-of-the-art in the development of metal/polymer composites as electrode materials for low-temperature fuel cells.

Carbon supported Pt and Pt–Ni (1:1) nanoparticles were prepared by reduction of metal precursors with NaBH 4 . XRD analysis indicated that only a small amount of Ni alloyed with Pt (Ni atomic fraction in the alloy about 0.05). The as-prepared catalysts were submitted to chronoamperometry (CA) measurements to evaluate their activity for the oxygen reduction reaction (ORR). CA measurements showed that the ORR activity of the as-prepared Ni-containing catalyst was higher than that of pure Pt. Then, their stability was studied by submitting these catalysts to durability tests involving either 30 h of constant potential (CP, 0.8 V vs. RHE) operation or repetitive potential cycling (RPC, 1000 cycles) between 0.5 and 1.0 V vs. RHE at 20 mV s −1 . After 30 h of CP operation at 0.8 V vs. RHE, loss of all non-alloyed Ni, partial dissolution of the Pt–Ni alloy and an increase of the crystallite size was observed for the Pt–Ni/C catalyst. The ORR activity of the Pt–Ni/C catalyst was almost stable, whereas the ORR activity of Pt/C slightly decreased with respect to the as-prepared catalyst. Loss of all non-alloyed and part of alloyed Ni was observed for the Pt–Ni/C catalyst following repetitive potential cycling. Conversely to the results of 30 h of CP operation at 0.8 V vs. RHE, after RPC the ORR activity of Pt–Ni/C was lower than that of both as-prepared Pt–Ni/C and cycled Pt/C. This result was explained in terms of Pt surface enrichment and crystallite size increase for the Pt–Ni/C catalyst.