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In this study, the electro-oxidation reaction of ethanol over Pd–Cu supported on Cu porphyrin (TPPCu) was investigated. The catalyst was synthesized using the microwave-assisted polyol method and physicochemically characterized by XRD, XPS, SEM, EDS, TEM, EDAX, UV–Vis, FTIR, and RBS. A Cu-enriched catalyst with Cu3Pd, Pd,Cu, and TPPCu phases was identified using XRD and XPS. However, according to the RBS results, the catalytic surface was enriched with Pd, indicating that the interaction between TPPCu and Pd–Cu allowed the presence of Pd on the surface, thus enhancing the catalytic response of the material. This synthesis prevented the deprotonation of porphyrin on the electrocatalyst, as confirmed by XPS analysis. Electrochemical studies based on cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the response of the catalyst to variations in the scan rate and increasing ethanol concentration. The electrochemical response of PdCu/TPPCu improved with an increasing number of cycles, indicating improved mass transport, thus improving its electrochemical response and tolerance to CO contamination. This catalyst exhibited a high electroactive surface area of 49.4 m2/g, which could be related to the presence of TPPCu as a support. The behavior of the catalyst on the anode of a fuel cell fed with ethanol, bioethanol, and bioethanol residues was evaluated. [ABSTRACT FROM AUTHOR]

The effect of structural ordering of the gas diffusion layer (GDL) due to nitrogen-doped graphene (N-graphene) for alkaline fuel cells (AFCs) (the most studied fuel cell technology) and metal-air fuel cells (MAFC), which are a kind of electrochemical devices capable of directly converting the chemical energy stored in metals into fuel, has been studied. Two GDLs were made using two different carbon morphologies with a clear difference in particle sizes. The size and number of particles are an important consideration since the GDL are assumed to be placed next to the catalyst bed in the fuel cell. The GDL contains a porous carbon substrate, which is made in one case of the N-graphene and in another case of activated carbon. N-graphene was obtained in a free-standing position using nitrogen plasma generated by a DC plasma torch. To ensure gas supply and water drainage the GDL substrate must be hydrophobized. Polytetrafluoroethylene (PTFE) fibers were obtained on the surface of both layers. In order to understand the gas diffusion properties of the fabricated GDLs, their polarization behavior was studied. Polarization curves, obtained by means of modeling, fully correspond to experimental data. An advantage of the layered structure of GDL based on N-graphene is demonstrated. [ABSTRACT FROM AUTHOR]

One of the significant drawbacks of the Direct Methanol Fuel Cells is the overpotential for the methanol oxidation reaction, which strongly limits the efficiency of this fuel cell. Furthermore, CO poisoning of Pt is considered to be a severe problem for these devices. In this work, electrocatalysts with suitable properties and outstanding performance have been developed for the oxidation reaction of methanol. PtCu and PtCuRu type materials have been synthesized through a relatively uncomplex, fast, highly reproducible, and easily scalable method. In turn, these materials have been subjected to a selective chemical dissolution process to enrich their surface with a higher density of active sites and surface defects. Evidence of alloy formation was found, specifically through XPS measurements on Ru 3d level. Besides, it was observed that with the trimetallic catalysts, which contain not only Cu but also Ru, the onset of CO electrooxidation is substantially reduced. Moreover, the leaching treatment further improves this value. This same trend was observed in the evaluation of methanol oxidation. Regarding the specific and mass activities, PtCuRu-le exhibits almost 240% and 195% higher SA and MA than commercial Pt, respectively. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is an important electrode reaction for several power sources. However, the reaction is sluggish and expensive noble-metal catalyst are generally needed. The high price of the noble metals has severely hindered the wide application of the related power sources. Therefore, it is a significant challenge to develop the low-cost and efficient non-precious metal electrocatalysts (NPMC) towards ORR. Herein, a typical biomass waste-pine needles has been used as precursor to prepare a porous carbon material, exhibiting superior catalytic activity toward ORR. An onset and half wave potential of ~ 0.96 and 0.72 VRHE were obtained in the alkaline solution, respectively. Furthermore, the activity of obtained NPMC can be further improved when it is mixed with the commercial carbon black. Our present results demonstrated that the biomass, such as pine needles, can be employed as promising carbon precursors for NPMC toward ORR. Transforming bio-waste into useful ORR catalyst. [ABSTRACT FROM AUTHOR]

Pt-based bimetallic alloys have attracted intensive interests as highly efficient and stable heterogeneous catalysts for fuel cell applications, and searching flexible free-standing nanomembranes has been on the research focus because of their promising applications in catalysis, nanoelectronics, batteries, and sensing. Herein, a flexible free-standing paper composed of FePt alloy nanoparticles on nitrogen-doped paper (FePt-NG paper) has been developed as integrated electrode towards electrocatalytic oxidation of formic acid. It is found that, N doping is beneficial for the well dispersion of FePt nanoparticles on NG paper. The synergistic effect between Fe and Pt, as well as N doping effect simultaneously assures the improved catalytic activity of FePt-NG paper, making it the promising flexible electrode for application in fuel cell system. Moreover, the synthesis strategy could be used for the construction of other free-standing electrode towards catalysis, sensing, and battery applications. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The low reactivity of the oxygen reduction reaction (ORR) occurring on the cathode surface is a great challenge for designing an effective proton exchange membrane fuel cell. In this work, we assess the possibility of Pd-skin/PdFe(111) alloy as the catalytic cathode for improving the performance of fuel cells. By using the density functional theory calculations, we studied the ORR activity and the stability of this alloy in the ORR environment. Looking at the energies of the reaction intermediates, Pd-skin/PdFe(111) alloy was found to be more reactive than the PdCo alloy studied previously. It was found that having a monolayer of Fe atoms beneath the Pd-skin layer maximizes the ORR activity and the dissolution potential. However, the calculations also showed that surface segregation of the Fe atoms would be an issue for the stability of the Pd-skin structure in ORR environment. Graphical abstract: [ABSTRACT FROM AUTHOR]

Carbon-supported Pt-Rh-Sn catalysts ( x: y: z = 3:1:4, 6:2:4, 9:3:4) are prepared by Pt, Rh, and Sn precursors reduction in different addition order. The materials are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques and are evaluated for the electrooxidation of ethanol in acidic media by cyclic voltammetry, chronoamperometry, and anode potentiostatic polarization. The influence of both the order in which the precursors are added and the composition of metals in the catalysts on the electrocatalytic activity and physico-chemical characteristics of Pt-Rh-Sn/C catalysts is evaluated. Oxidized Rh species prevail on the surface of catalysts synthesized by simultaneous co-precipitation, thus demonstrating the influence of synthesis method on the oxidation state of catalysts. Furthermore, high amounts of Sn in composites synthesized by co-precipitation result in very active catalysts at low potentials (bifunctional effect), while medium Sn load is needed for sequentially deposited catalysts when the electronic effect is most important (high potentials), since more exposed Pt and Rh sites are needed on the catalyst surface to alcohol oxidation. The Pt-Rh-Sn/C catalyst prepared by co-precipitation is the most active at potentials lower than 0.55 V (related to bifunctional effect), while the Pt-Rh-Sn/C catalyst, prepared by sequential precipitation (first Rh and, after drying, Pt + Sn), is the most active above 0.55 V. [ABSTRACT FROM AUTHOR]

A new diagnosis method based on the measurement of the magnetic field surrounding a PEMFC stack was developed. The method relies on the measurements of the magnetic field signature generated by the current distribution in the PEMFC. It is possible to estimate an averaged 2D current density identification by solving an inverse problem, based on the relationship between the currents and a magnetic field. In this work, 30 sensors fixed around the stack are used to perform the cartography within a second. This technique was implemented on a PEMFC stack consisting of 30 cells with a large active area of 220 cm and was capable to capture the current density change from a healthy state to a faulty one. Our approach is robust and allows us to distinguish between either membrane drying or electrode flooding by varying the air stoichiometry. [ABSTRACT FROM AUTHOR]

In the current study, a nanoscale perovskite SrFeO (SrFNPs) was synthesized by a rapid microwave-assisted co-precipitation method and characterized by X-ray diffraction, Fourier transform-infrared spectroscopy, scanning electron microscopy, Energy dispersive X-ray, and vibrating sample magnetometer techniques. Modified glassy carbon electrode with Pt nanoparticles (PtNPs), functionalized carbon nanotubes (CNTs), and SrFNPs as multifunctional catalyst is prepared and its catalytic activity toward methanol oxidation is investigated. Based on the electrochemical studies, a PtNPs-CNTs-SrFNPs nanocomposite was shown a considerable activity for methanol oxidation in comparison of PtNPs, PtNPs-CNTs, and PtNPs-SrFNPs. A direct methanol fuel cell was designed, assembled, and tested with suggested PtNPs-CNTs-SrFNPs nanocomposites under several different conditions. The effect of some experimental factors such as temperature, methanol concentration, and flow rate as well as NaOH concentration on electrical performances of fuel cell were studied and optimized. [ABSTRACT FROM AUTHOR]

Incorporation of palladium nanoparticles (PdNPs) and multi-walled carbon nanotubes (MWCNTs) into chitosan-coated glassy carbon (GC) electrode for alcohols (methanol, ethanol, and isopropanol) electrooxidation has been studied. PdNPs-chitosan and MWCNTs-PdNPs-chitosan nanocomposites are successfully prepared and characterized by transmission electron microscopy images and UV-Vis spectroscopy. Based on the results, PdNPs-chitosan nanocomposite indicates high electrochemical activity and excellent catalytic characteristic for alcohol (C-C) electrooxidation on a GC electrode in an alkaline medium. The current density of the alcohols oxidation at GC-PdNPs-chitosan electrode is investigated in optimized conditions and compared with that obtained at the GC-modified electrode by Pd with different polymers. Also, our results show that the dispersion of Pd nanoparticles on the MWCNTs significantly improved the performance of the PdNPs/chitosan composite for electrooxidation of the C-C alcohols. [ABSTRACT FROM AUTHOR]

This paper shows by thorough electrochemical investigation that (1) the performances of high-temperature polymer electrolyte fuel cell membrane electrode assemblies of three suppliers are differently affected by compressive forces. (2) Membrane thickness reduction by compressive pressure takes place less than expected. (3) A contact pressure cycling experiment is a useful tool to distinguish the impact of compression on the contact resistances bipolar plate/gas diffusion layer (GDL) and GDL/catalytic layer. A detailed visual insight into the structural effects of compressive forces on membrane and gas diffusion electrode (GDE) is obtained by micro-computed X-ray tomography (μ-CT). μ-CT imaging confirms that membrane and GDEs undergo severe mechanical stress resulting in performance differences. Irreversible GDL deformation behavior and pinhole formation by GDL fiber penetration into the membrane could be observed. [ABSTRACT FROM AUTHOR]

The behavior of a polybenzimidazole-based high-temperature polymer electrolyte membrane fuel cell using dimethyl ether (DME) as fuel was investigated under stationary and dynamic load conditions. The power density was enhanced significantly with an increase of both operating temperature and anodic water stoichiometry. Likewise, the power density decreased with increasing DME stoichiometry. The characterization of the dynamic operation showed a strong qualitative similarity to low-temperature direct methanol fuel cells. The development of the cell voltage after a spontaneous change of cell current density could be assigned to the electrochemical oxidation of an intermediate species. [ABSTRACT FROM AUTHOR]

PBI-based polymer electrolyte membrane (PEM) fuel cells have short durability comparing with Nafion ones. It is known that the presence of phosphoric acid accelerates catalyst sintering, and the polymer is susceptible to getting degraded via oxidative degradation. However, the influence of the current distribution on the degradation process has not been investigated. In this work, current distribution was measured continuously during a steady state life test that was performed in a 50-cm PBI-PEM fuel cell. The membrane-electrode assembly was prepared using techniques that are supposed to ensure satisfactory reproducibility at global level. Two different stages, i.e., activation and degradation, were identified. They show disparities in both global and local performance. It was found that the current distribution map is very heterogeneous, with variations around ±50 % with respect to the average value during the whole lifetime of the cell. The non-uniformity of the current profile increases during the degradation, but it cannot be concluded that the current density distribution contributes to the short lifetime. [ABSTRACT FROM AUTHOR]

A Pd/C electrode modified by HPMoO was prepared and its catalytic performance for HO electroreduction in acidic medium was investigated by cyclic voltammograms. Pd nanoparticles supported on Vulcan XC-72 carbon were prepared by chemical reduction of PdCl in aqueous solution using NaBH as the reducing agent. X-ray diffraction analysis indicated that the particle size of Pd is around 9.7 nm. The modified electrode was prepared by cyclic voltammograms in HSO solution containing HPMoO. The results showed that HPMoO can efficiently enhance the electrocatalytic activity for HO electroreduction on Pd/C. The effect of HPMoO content on the electrocatalytic activity of the catalyst was also investigated by CV. The best results appeared at the concentration of HPMoO = 0.5 mmol L. [ABSTRACT FROM AUTHOR]

The topic of this study is the optimization of the preparation procedure and chemical composition of a gas diffusion electrode (GDE) for utilization in high-temperature PEM fuel cells. A phosphoric acid-doped polybenzimidazole derivative membrane was used as a polymer electrolyte. The following parameters were studied: nature and content of the polymeric binder (PTFE-hydrophobic, PBI-hydrophilic) in the catalytic layer (CL) and concentration of platinum in catalytic powder (affecting the thickness of the CL). Brushing and spraying were selected as the most suitable techniques of CL deposition. Surprisingly, both polymeric binders investigated in the framework of this study were found to provide a similar GDE performance for CL deposited on the gas diffusion layer surface by spraying. [ABSTRACT FROM AUTHOR]

elerated electrochemical corrosion of nitrogen-containing carbon (CN) oxygen reduction catalysts was performed by a chronoamperometric hold at 1.2 V versus NHE in acidic electrolyte using a rotating disk electrode system. Cyclic voltammograms were used to measure the electrochemically active quinone/hydroquinone redox reaction couple indicating the degree of carbon corrosion. Half-cell testing of CN oxygen reduction catalyst materials showed superior carbon corrosion resistance compared to Vulcan carbon, the most ubiquitous cathode catalyst support. When oxygen reduction activity was measured before and after carbon corrosion, carbon corrosion resilience trended with the oxygen reduction activity. CN catalysts subjected to carbon corrosion testing did not show a change in the onset of oxygen reduction reaction (ORR) activity potentials with only a slight reduction in current density, but showed improved ORR selectivity to the complete reduction of dioxygen to water. [ABSTRACT FROM AUTHOR]

In this study a Photoelectrochemical Cell (PEC) constructed with inexpensive materials photodegraded selected organic compounds present in model waste waters, with the concomitant production of electrical current. Organic substrates dissolved in salt water included formic acid, 2-propanol, 1,2-dihydroxybenzene and ascorbic acid. Significant degradation of ascorbic acid was achieved when the cell was illuminated with a household 60 W tungsten light bulb, although better results were achieved with UV sources. Degradation of all the compounds was found to occur by zero order kinetics, and the PEC was shown not to work appreciably in dark conditions. Using a conventional light bulb, a formic acid PEC produced a power density of 19.1 ± 2 mW m. When exposed to natural daylight, a power density of 31.5 ± 2 mW m was achieved. There is considerable scope for scale up of this device for exterior use. [ABSTRACT FROM AUTHOR]

dvancements in the performance of the direct methanol redox fuel cell (DMRFC) were made through anolyte/catholyte composition and cell temperature studies. Catholytes prepared with different iron salts were considered for use in the DMRFC in order to improve the catholyte charge density (i.e., iron salt solubility) and fuel cell performance. Following an initial screening of different iron salts, catholytes prepared with FeNH(SO), Fe(ClO) or Fe(NO) were selected and evaluated using electrolyte conductivity measurements, cyclic voltammetry and fuel cell testing. Solubility limits at 25 °C were observed to be much higher for the Fe(ClO) (>2.5 M) and Fe(NO) (>3 M) salts than FeNH(SO) (~1 M). The Fe(ClO) catholyte was identified as a suitable candidate due to its high electrochemical activity, electrochemical reversibility, observed half-cell potential (0.83 V vs. SHE at 90 °C) and solubility. DMRFC testing at 90 °C demonstrated a substantial improvement in the non-optimized power density for the perchlorate system (79 mW cm) relative to that obtained for the sulfate system (25 mW cm). Separate fuel cell tests showed that increasing the cell temperature to 90 °C and increasing the methanol concentration in the anolyte to 16.7 M (i.e., equimolar HO/CHOH) yield significant DMRFC performance improvements. Stable DMRFC performance was demonstrated in short-term durability tests. [ABSTRACT FROM AUTHOR]

Macrocyclic compounds such as metallophthalocyanines demonstrated good catalytic activities toward electrochemical reactions. The characteristics of the central cations in metallophthalocyanines significantly influenced their electrocatalytic activities. Addition of conjugated polymers in electrodes improved the electrocatalytic activity by enhancing the electric conductivity. The electrocatalytic activities of macrocyclic compounds could be further improved by heat treatment. The formation of metallic clusters or metal containing organic fragments after pyrolyzing played an important role in improving electrocatalytic activities of macrocyclic compounds. It was considered that macrocyclic compounds might be functioned as a precursor to obtain well-distributed metallic clusters or metal containing organic fragments. [ABSTRACT FROM AUTHOR]

The performance of macrocyclic catalysts in oxygen reduction was investigated for a direct methanol fuel cell. The dependence of catalytic activity on different factors was determined for two classes of precursors; namely, iron porphyrin (Fe-PC) and iron phthalocyanine (Fe-TPP). It was found that there was an optimal heat-treating temperature for each precursor. Heat-treated Fe-TPP shows maximum activity at 750 °C, while the highest performance in the case of Fe-PC is observed at 500 °C. It was shown that oxygen reduction activity is affected by the number of nitrogen bonds formed with iron, particle size, and formation of carbon layers. [ABSTRACT FROM AUTHOR]

We present a complete testing environment for the parallel performance characterization of biofuel cells. Besides rapid-assembly electrode fixtures and an aseptic electrochemical reactor, it comprises a 24-channel electrical testing system that bridges the gap between simple load resistors and costly multi-channel potentiostats. The computer-controlled testing system features active current control to enable the forced operation of half-cell electrodes, whereas galvanic isolation between individual channels ensures interference-free operation of multiple fuel cells immersed in a common testing solution. Implemented into the control software is an automated procedure for the step-wise recording of polarization curves. This way, performance overestimation due to a too fast increase in load current can be circumvented. As an applicational example, three abiotically catalyzed glucose fuel cells are characterized simultaneously in a common testing solution. Complete disclosure of the electrical system (incl. printed circuit board layout, control software, and circuit diagrams) in the online supplementary material accompanying this paper allows researchers to replicate our setup in their lab and can serve as inspiration for the design of similar systems adapted to specific requirements. [ABSTRACT FROM AUTHOR]

PtSn/CeO2–C electrocatalyst was prepared in a single step by an alcohol-reduction process using ethylene glycol as solvent and reducing agent and CeO2 (15 wt%) and Vulcan XC72 (85 wt%) as supports. The performance for ethanol oxidation was investigated by cyclic voltammetry and in situ FTIR spectroscopy. The electrocatalytic activity of the PtSn/CeO2–C electrocatalyst was higher than that of the PtSn/C electrocatalyst. FTIR studies for ethanol oxidation on PtSn/C electrocatalyst showed that acetaldehyde and acetic acid were the principal products formed, while on PtSn/CeO2–C electrocatalyst the principal products formed were CO2 and acetic acid. [ABSTRACT FROM AUTHOR]

The sub-freezing endurance of proton exchange membrane (PEM) fuel cells with hydrophobic and hydrophilic catalyst-coated membranes (CCMs) was investigated. The polarization curves, electrochemical characteristics and physical structures of the CCMs were measured. The cells were frozen at −20 °C with saturated residual water after operating at 60 °C. After eight freeze/thaw cycles, no evident negative effect on the performance of the cell with a hydrophobic CCM was observed, while the cell with a hydrophilic CCM degraded severely. By analyzing the polarization curves, it was concluded that the mass transport limitation was the main reason for the performance loss of the hydrophilic cell. The electrochemical active surface area (ECA) results suggest that the hydrophobicity of the catalyst layer (CL) has an apparent impact on the residual water distribution of the membrane electrode assembly (MEA). A larger water content in the hydrophilic CL has a negative effect on the subzero endurance. From the polarization resistance obtained from electrochemical impedance spectroscopy (EIS) the origin of degradation was further clarified. Mercury intrusion porosimetry showed that the pore size of the hydrophilic catalyst layer changed significantly after freezing; the mean pore size increased from 5.68 to 6.71 nm. However, with a water removal method, namely, gas purging, it was possible to prevent degradation effectively. [ABSTRACT FROM AUTHOR]

A method for a rough estimation of the catalyst surface area in a fuel cell is developed. It is based on the deconvolution of experimental CO oxidation data by use of a mathematical model. The kinetic parameters of the model are determined by fitting the experimental curves. The experimental data are collected at different sweep rates (2–100 mV s−1) and at different temperatures (room −60.0 °C). The model can predict the sweep rate dependence of the CO oxidation onset potential, the peak current, the peak potential and the peak broadness. The model is further used for the prediction of the baseline in the presence of CO and for calculation of the CO charge consumed up to half peak potential. It is obtained that the latter value is constant at different sweep rates and that the baseline deviates from linearity already at low sweep rates (2 mV s−1), but not very significantly (2.0% in comparison to 8.8% at 100 mV s−1, based on calculated CO charge). It is suggested that lower sweep rates should be used for experimental surface area determination. [ABSTRACT FROM AUTHOR]

Pd–Ru, Pd and Ru nanoparticles supported on Vulcan XC-72 carbon were prepared by chemical reduction of PdCl2 and/or RuCl3 in aqueous solution using NaBH4 as the reducing agent. Transmission electron microscopy measurements showed that Pd–Ru particles were uniformly dispersed on carbon. The particle size of Pd–Ru is around 5–9 nm. X-ray diffraction analysis indicated that Ru formed alloy with Pd in Pd–Ru/C catalyst. The electroreduction of hydrogen peroxide on Pd–Ru/C, Pd/C and Ru/C in H2SO4 solution was examined by linear sweep voltammetry and chronoamperometry measurements. Results revealed that Pd–Ru/C catalyst exhibited higher electrocatalytic activity for hydrogen peroxide reduction than Pd/C and Ru/C. All the catalysts showed good stability for hydrogen peroxide electroreduction in H2SO4 electrolyte. [ABSTRACT FROM AUTHOR]

A family of proton conducting membranes based on cross-linked poly(vinyl alcohol), PVA, has been synthesized and characterized. The influence of surface-functionalized silica particles on the membrane properties has been evaluated by means of 1H-NMR, vibrational spectroscopy, thermal analysis and electrochemical characterization. The study revealed that the crystallinity of the polymer, the proton diffusivity and the water retention are strongly affected by the presence of the inorganic compound. Conductivity measurements and preliminary fuel cell tests agreed in determining the best PVA/silica ratio among the various compositions explored and demonstrated the potentiality of the selected membranes as electrolytes in fuel cell devices. [ABSTRACT FROM AUTHOR]

This paper describes an investigation of the role of nickel phthalocyanine-tetrasulfonic acid (NiPcTs) for methanol electro-oxidation on a Pt/C catalyst. Cyclic voltammetry (CV) revealed that NiPcTs has no catalytic activity in methanol or CO electro-oxidation. However, methanol electro-oxidation occurs faster on a Pt/C catalyst modified with NiPcTs than on the original Pt/C catalyst. CO stripping results demonstrated that NiPcTs promotes electro-oxidation of adsorbed CO (COads) on the Pt/C catalyst, which is likely to be responsible for the enhancement of the methanol electro-oxidation rate. The promotion effect of NiPcTs is attributable to its ability to modify the electron density of the Pt surface. The electron deficiency of Pt0 in the NiPcTs-Pt/C catalyst is shown by the shift of the Pt0 4f peak to higher binding energies in the X-ray photoelectron spectrum. [ABSTRACT FROM AUTHOR]

The aim of this work is the study of the effectiveness of different parameter estimation techniques for proton exchange membrane fuel cells (PEMFC) under normal operating conditions. The procedure for the estimation of the real time parameters described herein in good approximation meets the requirements posed regarding such techniques, i.e., to obtain data without interrupting the functioning of the fuel cell and to be as simple as possible. In this approach a fuel cell combined with a step-down voltage regulator system was analyzed and the potential relaxation was used to determine PEMFC electrochemical properties. A screening measurement technique was applied using the analysis of variance (ANOVA) to elucidate the effect of the different operating conditions on the obtained parameter, hence to validate the developed algorithm. The results show that the operating conditions of the step-down regulator device affect some parameters, but the weak correlations predict that the method can be used in real applications. [ABSTRACT FROM AUTHOR]

In order to provide insight into the interfacial relationships at fuel cell electrodes, a measuring technique based on a scanning tunneling microscope working in an electrochemical cell has been developed. The structure of model electrodes consisting of carbon supported Pt and ionomer mixtures as well as MEA electrode surfaces is imaged by the electrochemical scanning tunneling microscope (EC-STM) from microscale to nanoscale. Images with subnanometer resolution are obtained indicating that some ordering of the particles on the carbon support is present in the model system and in the MEA. It is demonstrated that in both cases nanometer structures can be imaged reliably and that the interface is rather clean and active under reaction conditions. In addition, a technique has been developed to measure the local reactivity by using the STM tip as a sensor electrode for the ORR. [ABSTRACT FROM AUTHOR]

The use of hydrogen fuel cells for cars is strongly promoted by the governments of many countries and by international organizations like the European Community. The electrochemical behaviour of the most promising fuel cell (polymer electrolyte membrane fuel cell, PEMFC) is critically discussed, based on results presented in the literature. Moreover, when some non- electrochemical aspects are taken into consideration, it is concluded that the prospects are not too bright. Moreover, the hydrogen-rich gas generated from small organics contains CO2 and a small amount of CO, its use easily leads to poisoning of the platinum gas diffusion anode in the fuel cell. Also the hydrogen storage problems are still not solved. [ABSTRACT FROM AUTHOR]

Data on the performance of a direct borohydride fuel cell (DBFC) equipped with an anion exchange membrane, a Pt–Ru/C anode and a Pt/C cathode are reported. The effect of oxidant (air or oxygen), borohydride and electrolyte concentrations, temperature and anode solution flow rate is described. The DBFC gives power densities of 200 and 145 mW cm−2 using ambient oxygen and air cathodes respectively at medium temperatures (60 °C). The performance of the DBFC is very good at low temperatures (ca. 30 °C) using modest catalyst loadings of 1 mg cm−2 for anode and cathode. Preliminary data indicate that the cell will be stable over significant operating times. [ABSTRACT FROM AUTHOR]

Cell potential and power performance for tubular microbial fuel cells utilising manure as fuel are reported. The microbial fuel cells do not use a mediator, catalysts or a proton exchange membrane. The cell design has been scaled up to a size of 1.8 m in length using electrodes of 0.4 m2 in area. The cell does not require a strictly controlled anaerobic environment and has potential practical applications when adapted into the form of a helix allowing fuel to flow through it. The cell could be used for power generation in remote applications. The peak power density of the cell is over 3 μW cm −2 (30 mW m−2). The performance can be improved by a more effective design of the interface between the anode and cathode chambers. [ABSTRACT FROM AUTHOR]

The present study focuses on the problem of using conducting polymers (CPs) in proton exchange membrane fuel cell technology. It covers the electrocatalytic properties of the CP/Pt composite, permeability of the CP film for H2, fixation of the compact CP film on the top of the Nafion® membrane and first results of its utilization in a fuel cell. The present results did not confirm a previously reported increase in CP/Pt composite electrocatalytic activity when compared to the commercially available carbon supported catalysts. The main reason seems to be the very low permeability of the compact CP film for the fuel. This may be an advantage with respect to the minimization of fuel cross-over, which is a serious problem in the direct methanol fuel cell. On the other hand, it represents a serious danger in water management of the fuel cell. This fact has been recognized and alternative solutions are presented. [ABSTRACT FROM AUTHOR]

Pt/C electrocatalysts were prepared from a solution of H2PtCl6 in ethylene glycol in the presence of XC-72 carbon by adding a small amount of sodium acetate as stabilizer. Repeated TEM images showed that the platinum nanoparticles were small and uniform in size and highly dispersed on XC-72 carbon supports when a small amount of sodium acetate solution was added to the synthesis solution. The Pt/C electrocatalysts exhibited very high electrocatalytic activity for liquid methanol oxidation. The effects of adding acetate on Pt particle size and size distribution are discussed. It is demonstrated that acetate can be used as a good stabilizer for preparing Pt/C catalyst with fine and uniform Pt particles. [ABSTRACT FROM AUTHOR]

Three different concepts for H2–Cl2 fuel cells have been evaluated. An ordinary PEM fuel cell based on a Nafion membrane, a fuel cell based on a combination of circulating hydrochloric acid and a Nafion membrane and a system based on a phosphoric acid doped Polybenzimidazole (PBI) membrane. None of the investigated systems were able to demonstrate stable operation under the conditions used in this study, due to electrocatalyst corrosion, membrane dehydration and/or electrode flooding. All systems studied achieved open circuit voltages close to the reversible thermodynamic value for production of aqueous hydrochloric acid, suggesting formation of dissolved HCl in the electrolyte and fast electrode kinetics. [ABSTRACT FROM AUTHOR]

The electrooxidation of DME was studied at a bulk platinum electrode. It was shown that the DME adsorption was a slow step in the overall oxidation reaction. The DME adsorption is potential dependent in the hydrogen region of platinum and independent in the double layer region. From low potential scan rate voltammetry and DME stripping experiments, it was shown that the DME oxidation mechanism occurred via several reaction paths. At low potentials, DME oxidation leads to the existence of a positive current plateau. “In situ” Infrared Reflectance Spectroscopy experiments were carried out to identify the intermediate and reaction products of DME adsorption and oxidation at different potentials. COL (linearly bonded CO), COB (bridge bonded CO), adsorbed COOH species and CO2 were detected. From these electrochemical and spectro-electrochemical results, it was proposed that some adsorbed DME was hydrolysed and directly oxidized to CO2 or HCOOH species and some partially blocked platinum sites at the surface forming Pt–CHO and/or Pt–CO. Then, as soon as platinum becomes able to activate water, a bifunctionnal mechanism occurs to form either HCOOH or CO2 again following two different reaction paths. [ABSTRACT FROM AUTHOR]

Pt black and PtRu black fuel cell anodes have been modified with Mo oxide and evaluated in direct methanol, formaldehyde and formic acid fuel cells. Mo oxide deposition by reductive electrodeposition from sodium molybdate or by spraying of the fuel cell anode with aqueous sodium molybdate resulted in similar performance gains in formaldehyde cells. At current densities below ca. 20 mA cm−2, cell voltages were 350–450 mV higher when the Pt catalyst was modified with Mo oxide, but these performance gains decreased sharply at higher current densities. For PtRu, voltage gains of up to 125 mV were observed. Modification of Pt and PtRu back catalysts with Mo oxide also significantly improved their activities in direct formic acid cells, but performances in direct methanol fuel cells were decreased. [ABSTRACT FROM AUTHOR]

Membrane-electrode assemblies (MEAs) for direct methanol fuel cells (DMFC) have been prepared by depositing platinum on the surface of solid polymer electrolytes (SPE). Chemical and electrochemical depositions were used to achieve good adhesion between platinum particles and the SPE and for reducing the contact resistance. Platinum particle structure and composition were investigated by means of SEM and EDX. Cyclic voltammetry (CV) and methanol oxidation tests were used to determine the electrochemical characteristics of the Pt-SPE electrodes which can be applied in DMFC. Overall the electrodes produced by chemical and electrochemical deposition of Pt onto the membranes are not as active as those produced by hot pressing carbon supported Pt catalyst layers onto the membrane. [ABSTRACT FROM AUTHOR]

PtRu/C and PtSn/C electrocatalysts were prepared by the alcohol-reduction process with different atomic ratios. The electrocatalysts were characterized by EDAX, XRD, TEM and cyclic voltammetry and the electro-oxidation of ethylene glycol was studied by cyclic voltammetry and chronoamperometry using the thin porous coating technique. PtRu/C and PtSn/C electrocatalysts were found to be active for ethylene glycol oxidation, which starts at lower potentials by increasing the ruthenium and tin content. In the region of interest for direct alcohol fuel cell applications PtSn/C electrocatalysts were more active than PtRu/C electrocatalysts. [ABSTRACT FROM AUTHOR]

The effects of hot pressing of electrodes onto Nafion® membranes in the preparation of membrane and electrode assemblies for direct methanol fuel cells have been investigated. Hot pressing does not significantly influence the cell resistance or methanol crossover, but it can decrease cell performance by restricting mass transport in the anode catalyst layer. It also increases the time required for the cell to reach optimum performance. Best performances were obtained with membrane and electrode assemblies that had not been pressed. It was also found that membranes that had not been subjected to hot pressing could easily be re-used, making recycling of membranes and catalysts more feasible. [ABSTRACT FROM AUTHOR]

This study reports a two-dimensional numerical simulation of a steady, isothermal, fully humidified polymer electrolyte membrane (PEM) fuel cell, with particular attention to phenomena occurring in the catalyst layers. Conservation equations are developed for reactant species, electrons and protons, and the rate of electrochemical reactions is determined from the Butler–Volmer equation. Finite volume method is used along with the alternating direction implicit algorithm and tridiagonal solver. The results show that the cathode catalyst layer exhibits more pronounced changes in potential, reaction rate and current density generation than the anode catalyst layer counterparts, due to the large cathode activation overpotential and the relatively low diffusion coefficient of oxygen. It is shown that the catalyst layers are two-dimensional in nature, particularly in areas of low reactant concentrations. The two-dimensional distribution of the reactant concentration, current density distribution, and overpotential is determined, which suggests that multi-dimensional simulation is necessary to understand the transport and reaction processes occurring in a PEM fuel cell. [ABSTRACT FROM AUTHOR]

The role of the fluoropolymer matrix in the stability of irradiation grafted proton conducting membranes under fuel cell conditions is investigated. The structure of a series of membranes with poly(vinylidene fluoride), poly(vinylidene fluoride-co-hexafluoropropylene), poly(tetrafluoroethylene-co-hexafluoropropylene), and poly(ethylene-alt-tetrafluoroethylene) matrices with poly(styrene sulfonic acid) side chains is studied before and after a fuel cell test using X-ray scattering techniques and confocal micro-Raman spectroscopy. All tested membranes suffer from a loss of poly(styrene sulfonic acid) leading to a decrease in conductivity. Changes in crystallinity, lamellar period, orientation and thickness of the membranes are reported and compared to corresponding properties of the initial polymer films and the pristine membranes. The membranes where most severe changes in the structure of the matrix polymer can be observed have the shortest lifetimes in the fuel cell. [ABSTRACT FROM AUTHOR]

A H2/Cl2 fuel cell system with an aqueous electrolyte and gas diffusion electrodes has been investigated and the effects of electrolyte concentration and temperature on the open circuit voltage (OCV) and cell performance have been evaluated. Furthermore, the kinetics and long-term stability of Pt as electrocatalyst have been studied under various conditions. in addition, the long-term stability of Rh electrocatalyst has been evaluated. The OCV obtained showed that the Cl2 reduction is more reversible than O2 reduction. The ohmic drop was determining the cell performance at high current densities. An output power of about 0.5 W cm-2 was achieved with this system. [ABSTRACT FROM AUTHOR]

Numerical simulation was conducted to study the potential and current density distributions at the active electrode surface of a solid oxide fuel cell. The effects of electrode deviation, electrolyte thickness and electrode polarization resistance on the measurement error were investigated. For a coaxial anode/electrolyte/cathode system where the radius of the anode is greater than that of cathode, the cathode overpotential is overestimated while the anode overpotential is underestimated. Although the current interruption method or impedance spectroscopy can be employed to compensate/correct the error for a symmetric electrode configuration, it is not useful when dealing with the asymmetric electrode system. For the purpose of characterizing the respective overpotentials in a fuel cell, the cell configuration has to be carefully designed to minimize the measurement error, in particular the selection of the electrolyte thickness, which may cause significant error. For the anode-support single fuel cell, it is difficult to distinguish the polarization between the anode and cathode with reference to a reference electrode. However, numerical results can offer an approximate idea about the source/cause of the measurement error and provide design criteria for the fuel cell to improve the reliability and accuracy of the measurement technique. [ABSTRACT FROM AUTHOR]

The cell performance of direct methanol fuel cells (DMFC) is 0.5 V at 0.5 A cm−2 under high pressure oxygen operation (3 bar abs.) at 110 °C. However, high oxygen pressure operation at high temperatures is only useful in special market niches. Therefore, our work has now focused on air operation of a DMFC under low pressure (up to 1.5 bar abs.). At present, a power density of more than 100 mW cm−2 can be achieved at 0.5 V on air operation at 110 °C. These measurements were carried out in single cells with an electrode area of 3 cm2 and the air stoichiometry only amounted to 10. The effects of methanol concentration and temperature on the anode performance were studied by pseudo half cell measurements and the results are presented together with their impact on the cell voltage. A cell design with an electrode area of 550 cm2, which is appropriate for assembling a DMFC stack, was tested. A three-celled stack based on this design revealed nearly the same power densities as in the small experimental cells at low air excess pressure and the voltage–current curves for the three cells were almost identical. At 110 °C a power output of 165 W at a stack voltage of 1.5 V can be obtained in the air mode. [ABSTRACT FROM AUTHOR]

An understanding of the overall mechanism of the electrooxidation of methanol is of considerable interest in relation to the optimization of the direct methanol fuel cell. This paper describes in detail the different steps in the oxidation of methanol on platinum-based electrocatalysts with the identification of the key adsorption steps and of the different intermediates involved. From these fundamental studies, it is shown how it is possible to design multimetallic electrocatalysts for the electrooxidation of methanol under experimental conditions suitable for fuel cell application. [ABSTRACT FROM AUTHOR]

A polymer electrolyte membrane fuel cell operational at temperatures around 150–200 °C is desirable for fast electrode kinetics and high tolerance to fuel impurities. For this purpose polybenzimidazole (PBI) membranes have been prepared and H3PO4-doped in a doping range from 300 to 1600 mol %. Physiochemical properties of the membrane electrolyte have been investigated by measurements of water uptake, acid doping level, electric conductivity, mechanical strength and water drag coefficient. Electrical conductivity is found to be insensitive to humidity but dependent on the acid doping level. At 160 °C a conductivity as high as 0.13 S cm−1 is obtained for membranes of high doping levels. Mechanical strength measurements show, however, that a high acid doping level results in poor mechanical properties. At operational temperatures up to 190 °C, fuel cells based on this polymer membrane have been tested with both hydrogen and hydrogen containing carbon monoxide. [ABSTRACT FROM AUTHOR]

The electrochemical behaviour of metallic cerium and cerium dioxide is analysed in molten Li2CO3–Na2CO3 under the anodic and cathodic conditions used for the molten carbonate fuel cells (MCFC). Chronopotentiometric measurements on metallic cerium rods or foils show the influence of CeO2 growth and the deviation from its stoichiometric composition. A study of the voltammetric characteristics of dissolved cerium at a gold electrode, of metallic cerium and cerium oxide is carried out in both oxidising and reducing MCFC atmospheres. Experimental evidence is given for the existence of a solid–solid cerium system: Ce2O3(s)|CeO2(s) and a system relative to dissolved cerium species Ce2O3(l)|CeO2(l). These systems are in agreement with thermodynamic predictions. Other more complex phenomena involving interactions with alkali species are discussed. [ABSTRACT FROM AUTHOR]

Stainless steel 304 substrates were coated with different materials in order to find a suitable coating material for corrosion protection of separator plates in molten-carbonate fuel cells (MCFCs). Five titanium carbonitride coatings differing in composition and morphology and a titanium monoxide coating were deposited with chemical vapour deposition techniques. Also double-layer coatings of TiN/Au and TiN/Ni were prepared. The coatings were tested on their corrosion protection of separator plates in four different environments: under MCFC-cathode or anode gas, at load or at open circuit conditions. The corrosion behaviour was characterized using cyclic voltammetry. Corrosion rates were determined with electrochemical methods and cross-section analyses of corrosion layers. Titanium nitride coatings showed the best corrosion protection. The titanium carbide and titanium monoxide coating showed respectively less and no protection. The thin gold and Ni-coatings were unstable. Under cathode gas, the most important corrosion protection is given by keeping the cell at load, and then a titanium nitride coating might provide lifetime protection. Under anode gas, corrosion is most severe at load conditions. A titanium nitride coating also gives corrosion protection, but not enough for lifetime protection. [ABSTRACT FROM AUTHOR]