Investigation of fuel and media flexible laminar flow-based fuel cells

We investigate the performance of air-breathing laminar flow-based fuel cells (LFFCs) operated with five different fuels (formic acid, methanol, ethanol, hydrazine, and sodium borohydride) in either acidic or alkaline media. The membraneless LFFC architecture enables interchangeable operation with different fuel and media combinations that are only limited by the actual anode catalyst used. Furthermore, operating under alkaline conditions significantly improves methanol and ethanol oxidation kinetics and stabilizes sodium borohydride. LFFCs operated with hydrazine and sodium borohydride as fuels exhibit power densities of 80 and 101 mW/cm², respectively. To optimize anode performance, particularly for ethanol electro-oxidation, we introduced a hydrogen cathode to the membraneless LFFC design which renders the cell an ideal platform for anode investigation. Here, we highlight two simple diagnostic methods, in situ single electrode studies and electrochemical impedance spectroscopy (EIS), for characterizing and optimizing the performance of a direct ethanol LFFC anode.     

Mo oxide modified catalysts for direct methanol, formaldehyde and formic acid fuel cells

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.     

Electrooxidation of methanol and formic acid on PtCu nanoparticles

Improving the catalytic activity of the anode catalyst is an important task in direct methanol and formic acid fuel cell development. In the present work, catalytic activity of shape-controlled PtCu nanoparticles toward methanol and formic acid oxidation was investigated. The results show that the addition of Cu to Pt increases the catalytic activity of both reactions. In addition, the shape of PtCu nanoparticles plays an important role on improving the reactivity of both reactions. Cubic PtCu nanoparticles are more active for methanol oxidation while spheres are better for formic acid oxidation. The present study demonstrates controlling shape of Pt alloy catalysts is an effective way of improving catalytic activity. Likely mechanisms of the activity enhancement are briefly discussed.     

Performance of the direct formic acid fuel cell with electrochemically modified palladium-antimony anode catalyst

Previous work has shown that palladium catalysts are quite active for formic acid electrooxidation, but the catalysts need to be periodically regenerated to remove a CO impurity from the surface. The objective of this paper is to determine whether antimony additions could suppress the CO formation under fuel cell conditions. We find that antimony doubles the rate of reaction in an electrochemical cell, but the increase is less in real fuel cell conditions. The current that is produced at 0.6 V is approximately 14% greater for the fuel cell containing antimony additions than the palladium anode catalyst. In a constant-current test, we find that the fuel cell assembled with palladium-antimony anode catalyst produces 18% more voltage than the palladium anode catalyst after 9 h of operation. These results show that the antimony additions that significantly improve oxidation in the electrochemical cell have a much lesser impact in the formic acid fuel cell - they do not suppress CO formation in the fuel cell as anticipated.     

Highly effective anode structure in a direct formic acid fuel cell

We report the mass transport characteristics of formic acid and performance enhancement in a direct formic acid fuel cell in terms of the property of anode components. The effect of hydrophobicity of anode diffusion media as well as catalyst layer was investigated applying different cell temperature and fuel concentration. The operation over 80 °C and concentrated formic acid is of great advantage to the enhancement of catalytic activity and better water management. On the other hand, the conductivity of formic acid decreases by means of the formation of more complex chains of formic acid and the fuel cell resistance increases by membrane dehydration effect due to the hygroscopic property of formic acid, resulting in overall decrease of cell performance and long-term stability. Optimizing operating conditions, the use of 60% PtRu/C with only 1 mg/cm² on plain carbon paper can be one of the good choice to achieve both sustainable power performance and higher utilization of anode catalysts keeping cell resistance.     

Formic acid oxidation by carbon-supported palladium catalysts in direct formic acid fuel cell

The oxidation of formic acid by the palladium catalysts supported on carbon with high surface area was investigated. Pd/C catalysts were prepared by using the impregnation method. 30 wt% and 50 wt% Pd/C catalysts had a high BET surface area of 123.7 m²/g and 89.9 m²/g, respectively. The fuel cell performance was investigated by changing various parameters such as anode catalyst types, oxidation gases and operating temperature. Pd/C anode catalysts had a significant effect on the direct formic acid fuel cell (DFAFC) performance. DFAFC with Pd/C anode catalyst showed high open circuit potential (OCP) of about 0.84 V and high power density at room temperature. The fuel cell with 50 wt% Pd/C anode catalyst using air as an oxidant showed the maximum power density of 99 mW/cm². On the other hand, a fuel cell with 50 wt% Pd/C anode catalyst using oxygen as an oxidant showed a maximum power density of 163 mW/cm² and the maximum current density of 590 mA/cm² at 60 °C.     

Poisoning and regeneration of Pd catalyst in direct formic acid fuel cell

Palladium catalyst poisoned in the anode of direct formic acid fuel cell (DFAFC) during constant current discharging can be fully regenerated by a non-electrochemical method, i.e. just switching pure water to DFAFC for 1 h. Electrochemical impedance spectrum of DFAFC during the discharging and regeneration were recorded and analyzed. No much difference could be found for the high-frequency resistance of DFAFC after discharging while the charge transfer resistance in the mediate-frequency region increased significantly. The voltage variation during the regeneration showed that one platform of 0.35 V was formed by the intermediate species of formic acid oxidation, which is proven to be critical for cell performance regeneration. The results indicated that the absorption of poisoning species on Pd was the main reason for the decaying of cell performance.     

直接甲醇燃料电池阳极非铂催化剂的研究进展

介绍了直接甲醇燃料电池(DMFC)的特点及其阳极催化剂存在的主要问题。综述了DMFC阳极非铂催化剂的研究进展及非铂催化剂对甲醇氧化的催化活性和抗CO等中间物毒化能力等性能,提出了DMFC阳极非铂催化剂存在的问题以及发展趋势。     

Performance characterization of direct formic acid fuel cell using porous carbon-supported palladium anode catalysts

Palladium particles supported on porous carbon of 20 and 50 nm pore diameters were prepared and applied to the direct formic acid fuel cell (DFAFC). Four different anode catalysts with Pd loading of 30 and 50 wt% were synthesized by using impregnation method and the cell performance was investigated with changing experimental variables such as anode catalyst loading, formic acid concentration, operating temperature and oxidation gas. The BET surface areas of 20 nm, 30 wt% and 20 nm, 50 wt% Pd/porous carbon anode catalysts were 135 and 90 m²/g, respectively. The electro-oxidation of formic acid was examined in terms of cell power density. Based on the same amount of palladium loading with 1.2 or 2 mg/cm², the porous carbon-supported palladium catalysts showed higher cell performance than unsupported palladium catalysts. The 20 nm, 50 wt% Pd/porous carbon anode catalyst generated the highest maximum power density of 75.8 mW/cm² at 25 °C. Also, the Pd/porous carbon anode catalyst showed less deactivation at the high formic acid concentrations. When the formic acid concentration was increased from 3 to 9 M, the maximum power density was decreased from 75.8 to 40.7 mW/cm² at 25 °C. Due to the high activity of Pd/porous carbon catalyst, the cell operating temperature has less effect on DFAFC performance.     

Pt–Sn/C electrocatalysts for methanol oxidation synthesized by reduction with formic acid

Carbon supported Pt–Sn alloy catalysts were prepared by reduction of Pt and Sn precursors with formic acid, and their electrocatalytic activity for methanol oxidation was compared with commercial Pt/C and Pt₇₅Sn₂₅/C electrocatalysts. By X-ray diffraction analysis it was found that the Pt lattice parameter increases with the addition of Sn, indicative of alloy formation. It was confirmed that Sn exhibits cocatalytic activity for CO oxidation. The onset potential for the methanol oxidation reaction of the Pt–Sn electrode was approximately 0.1 V smaller than that on Pt both at room temperature and at 90 °C. The best performance in a direct methanol fuel cell was obtained using the Pt₇₅Sn₂₅/C alloy catalyst prepared by the formic acid method as the result of an optimal balance of Sn content, degree of alloying and metal particle size.     

Influence of underpotentially deposited Sb onto Pt anode surface on the performance of direct formic acid fuel cells

We first reported on electrocatalytic activity and stability of antimony modified platinum (PtSb_upd) as anode catalyst in direct formic acid fuel cells. Sb modified Pt (PtSb_upd) was prepared by underpotential deposition technique applying constant potential of 0.2 V (vs. Ag/AgCl, 3M KCl) and its modified surface was characterized by XRD and XPS. The electrocatalytic oxidation activity by cyclic voltammograms and the single cell power performance of Sb modified Pt were measured and their results were compared with the data of unmodified Pt electrode. PtSb_upd induced lower onset potential of formic acid oxidation and twice higher power density of 250 mW cm⁻² was observed.     

Iron(III) tetramethoxyphenylporphyrin(FeTMPP) as methanol tolerant electrocatalyst for oxygen reduction in direct methanol fuel cells

Carbon supported iron (III) tetramethoxyphenylporphyrin (FeTMPP) heat treated at 800°C under argon atmosphere was used as catalysts for the electroreduction of oxygen in direct methanol polybenzimidazole (PBI) polymer electrolyte fuel cells that were operated at 150°C. The electrode structure was optimized in terms of the composition of PTFE, polymer electrolyte and carbon-supported FeTMPP catalyst loading. The effect of methanol permeation from anode to cathode on performance of the FeTMPP electrodes was examined using spectroscopic techniques, such as on line mass spectroscopy (MS), on line Fourier transform infrared (FTIR) spectroscopy and conventional polarization curve measurements under fuel cell operating condition. The results show that carbon supported FeTMPP heat treated at 800°C is methanol tolerant and active catalyst for the oxygen reduction in a direct methanol PBI fuel cell. The best cathode performance under optimal condition corresponded to a potent ial reached of 0.6V vs RHE at a current density of 900 mAcm–2.     

钯基催化剂应用于甲酸电氧化反应的研究进展

甲酸是一种很有前途的化学储氢材料,可作为低温液体燃料电池的直接燃料。钯基催化剂作为直接甲酸燃料电池（DFAFC）阳极材料,对甲酸氧化具有良好的催化活性,能克服一氧化碳的毒化,在甲酸电化学氧化反应中主要按直接途径进行。降低贵金属含量、提高催化活性、提升稳定性是当前钯基催化材料研究领域的主要方向。主要介绍了当前研究中钯催化剂对甲酸电氧化的催化机理,综述了近5 a的钯合金催化剂制备、特殊形貌控制、碳负载对甲酸氧化活性增强的研究,对钯基催化剂的持续开发具有实际应用意义。     

Carbon supported PtBi catalysts for direct formic acid fuel cells

Carbon supported PtBi bimetallic catalysts (PtBi/C) prepared by depositing Bi on a commercial Pt/C catalyst and by codeposition of Pt and Bi have been compared for formic acid oxidation in a multi-anode direct formic acid fuel cell. Both types of catalyst gave much higher cell performances than the Pt/C, with only low amounts of Bi (Pt to Bi mole ratios of 11:1 and 14:1, respectively) required for optimum performance. The high Pt to Bi ratio for the best codeposited catalyst indicates that the Bi was concentrated at the surface, and this is consistent with X-ray diffraction and X-ray photoelectron spectroscopy results. However, cyclic voltammetry revealed a strong electronic effect that is inconsistent with surface decoration. The effects of the Bi have been attributed to selective blocking of sites at which CO is formed.     

Performance of a direct methanol fuel cell

The performance of a direct methanol fuel cell based on a Nafion® solid polymer electrolyte membrane (SPE) is reported. The fuel cell utilizes a vaporized aqueous methanol fuel at a porous Pt–Ru–carbon catalyst anode. The effect of oxygen pressure, methanol/water vapour temperature and methanol concentration on the cell voltage and power output is described. A problem with the operation of the fuel cell with Nafion® proton conducting membranes is that of methanol crossover from the anode to the cathode through the polymer membrane. This causes a mixed potential at the cathode, can result in cathode flooding and represents a loss in fuel efficiency. To evaluate cell performance mathematical models are developed to predict the cell voltage, current density response of the fuel cell.     

Evaluation of direct formic acid fuel cells with catalyst layers coated by electrospray

We investigated cell performance and performed phenomenological analyses of direct formic acid fuel cells (DFAFCs) incorporating anode (palladium) and cathode (platinum) catalysts prepared using a new electrospray coating technique. To optimize the design of the DFAFC, we examined the cell performance by the Pd catalyst loading and formic acid feed rate. Of Pd catalyst loaded samples, 3 mg/cm² sample showed the highest electrical performance with formic acid feed rate of 5 ml/min. This behavior was caused by discrepancies in the mass transfer limitation. When the feed rate was greater than 10 mL/min, however, the 7 mg/cm² sample provided the highest electrical performance, which was attributed to enhanced electrooxidation reactions. For comparison of the effect of the catalyst coating method on the cell performance of DFAFC, polarization curves of the DFAFC incorporating catalysts prepared using a conventional airspray coating method were also measured. As a result of the comparison, the electrospray coatingused DFAFC showed better cell performance. Based on these results, the cell performance of the DFAFCs was optimized when the catalysts using the electrospray catalyst coating were employed, the amount of Pd loaded on the anode electrode was 3 mg/cm² (Pd thickness: ∼6 μm), and the formic acid feed rate was 10 mL/min.     

Pt/laponite clay-modified gold electrode for direct methanol fuel cells

This work employs a novel technique in which laponite clay-modified gold electrodes are used as the anode for direct methanol fuel cells. The platinum/laponite clay (Pt/Clay) films on indium tin oxide electrode were characterized by using scanning electron microscope and energy-dispersive X-ray spectroscopy. Various contents of laponite clay (0.1, 0.5, 1.0, and 2.0?wt%) with constant platinum (Pt) catalyst content on modified gold electrodes were studied as an anode catalyst for methanol oxidation. The catalyst poisoning was observed as a function of time. The 1.0?wt% Pt/Clay-modified gold electrode shows the highest activity for methanol oxidation, 27.73?% higher than Pt only modified gold electrode at 2.5?min. The peak current of 1?% Pt/Clay-modified gold electrode is 3.50?% higher than the peak current of Pt only modified gold electrode at 57.5?min. The higher content of Pt/Clay-modified gold electrode shows strong resistance to catalyst poisoning. The Pt/Clay-modified gold electrode is a new and promising electrode for a direct methanol fuel cell and can replace existing commercial catalysts.     

Nanoporous PdNi/C Electrocatalyst Prepared by Dealloying High‐Ni‐content PdNi Alloy for Formic Acid Oxidation

To improve the electrochemical performance of Pd‐based catalysts for formic acid oxidation, a carbon supported nanoporous PdNi catalyst is prepared by dealloying high‐Ni‐content PdNi alloy nanoparticles in acid solution. The structure of nanoporous PdNi/C catalyst is characterized by X‐ray diffraction, transmission electron microscopy and X‐ray photoelectron spectroscopy. The electrocatalytic results show that the activity of the nanoporous PdNi/C catalyst is higher than that of nonporous Pd/C catalyst. The results demonstrate that the carbon‐supported nanoporous PdNi catalyst has a potential for application in direct formic acid fuel cells.     

Variations in interfacial properties during cell conditioning and influence of heat-treatment of ionomer on the characteristics of direct methanol fuel cells

Variations in interfacial properties in the anode catalyst layer during cell conditioning were characterized, and influence of the heat-treatment of ionomer on the characteristics of direct methanol fuel cells was investigated in this work. The anode catalyst layer was made by mixing a solvent-substituted Nafion solution with unsupported Pt/Ru black and curing the mixture in an oven with an inert environment. Materials characterization (SEM and optical microscopy) and electrochemical characterization (cell polarization, anode polarization, electrochemical impedance spectroscopy, and CO-stripping cyclic voltammetry) were performed. During cell conditioning, the enhanced kinetics of MeOH electrochemical oxidation and severe limiting current phenomenon are due to the combination of variations in interfacial properties and swelling of ionomer in the anode catalyst layer over time. Ru oxides at the catalyst surface are reduced continuously during cell conditioning. The nearly constant integrated areas under the CO-stripping CV peaks and broadened peak shapes indicate a stable number of Pt/Ru bimetallic alloy surface sites, yet the surface composition distribution is broadened. Heat-treatment influences ionomer crystallinity, altering its swelling behavior and hence affecting the characteristics of the direct methanol fuel cell (DMFC) anode.     

直接甲醇燃料电池

介绍了直接甲醇燃料电池的原理、结构,并与发展较早的氢气燃料电池进行优劣比较。针对近期商业化便携式燃料电池的技术指标,主要讨论了直接甲醇燃料电池在性能和成本上的现状和问题,并着重阐述了阳极催化剂和电解质膜(决定其性能的两个关键因素)的研发进展。