Current efficiency for soybean oil hydrogenation in a solid polymer electrolyte reactor

Soybean oil has been hydrogenated electrocatalytically in a solid polymer electrolyte (SPE) reactor, similar to that in H2/O2 fuel cells, with water as the anode feed and source of hydrogen. The key component of the reactor was a membrane electrode assembly (MEA), composed of a precious metal-black cathode, a RuO2 powder anode, and a Nafion® 117 cation-exchange membrane. The SPE reactor was operated in a batch recycle mode at 60°C and one atmosphere pressure using a commercial-grade soybean oil as the cathode feed. Various factors that might affect the oil hydrogenation current efficiency were investigated, including the type of cathode catalyst, catalyst loading, the cathode catalyst binder loading, current density, and reactant flow rate. The current efficiency ordering of different cathode catalysts was found to be Pd>Pt>Rh>Ru>Ir. Oil hydrogenation current efficiencies with a Pd-black cathode decreased with increasing current density and ranged from about 70% at 0.050Acm–2 to 25% at 0.490Acm–2. Current pulsing for frequencies in the range of 0.25–60Hz had no effect on current efficiencies. The optimum cathode catalyst loading for both Pd and Pt was 2.0mgcm–2. Soybean oil hydrogenation current efficiencies were unaffected by Nafion® and PTFE cathode catalyst binders, as long as the total binder content was 30wt% (based on the dry catalyst weight). When the oil feed flow rate was increased from 80to 300mlmin–1, the oil hydrogenation current efficiency at 0.100Acm–2 increased from 60% to 70%. A high (70%) current efficiency was achieved at 80mlmin–1 by inserting a nickel screen turbulence promoter into the oil stream.     

A direct methanol fuel cell using acid-doped polybenzimidazole as polymer electrolyte

A direct methanol/oxygen solid polymer electrolyte fuel cell was demonstrated. This fuel cell employed a 4 mg cm^–2 Pt-Ru alloy electrode as an anode, a 4 mg cm^–2 Pt black electrode as a cathode and an acid-doped polybenzimidazole membrane as the solid polymer electrolyte. The fuel cell is designed to operate at elevated temperature (200°C) to enhance the reaction kinetics and depress the electrode poisoning, and reduce the methanol crossover. This fuel cell demonstrated a maximum power density about 0.1 W cm^–2 in the current density range of 275–500 mA cm^–2 at 200°C with atmospheric pressure feed of methanol/water mixture and oxygen. Generally, increasing operating temperature and water/methanol mole ratio improves cell performance mainly due to the decrease of the methanol crossover. Using air instead of the pure oxygen results in approximately 120 mV voltage loss within the current density range of 200–400 mA cm^–2 .     

Optimization of operating parameters of a direct methanol fuel cell and physico-chemical investigation of catalyst–electrolyte interface

A physico-chemical investigation of catalyst–Nafion® electrolyte interface of a direct methanol fuel cell (DMFC), based on a Pt–Ru/C anode catalyst, was carried out by XRD, SEM-EDAX and TEM. No interaction between catalyst and electrolyte was detected and no significant interconnected network of Nafion micelles inside the composite catalyst layer was observed. The influence of some operating parameters on the performance of the DMFC was investigated. Optimal conditions were 2 M methanol, 5 atm cathode pressure and 2–3 atm anode pressure. Power densities of 110 and 160 mW cm⁻² were obtained for operation with air and oxygen, respectively, at temperatures of 95–100°C and with 1 mg cm⁻² Pt loading.     

Electrosynthesis of p-hydroxybenzaldehydefrom sodium p-hydroxymandelate

The electrosynthesis of p-hydroxybenzaldehyde (PHB) from sodium p-hydroxymandelate (SPHM) was investigated and good synthesis conditions were obtained. The electrochemical reactor was a divided filter-press with carbon felt electrodes (anode and cathode). Two different anolytes were used depending on the membrane employed. Thus, a 0.6m SPHM 2.7m NaOH solution was used in conjunction with a cationic Nafion® 117 membrane while a 0.6m SPHM in 1.8m NaOH solution was employed with an anionic Ionac® MA-3475 membrane. The electrolysis was carried out at a constant current density of 100mAcm–2. A material yield of approximately 90% was obtained at an energy cost of 1.4–1.5kWhkg–1 PHB and a production of 49kg PHBm–2 day–1.     

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.     

Material aspects of the liquid feed direct methanol fuel cell

A study of a small scale Liquid Feed Direct Methanol Fuel Cell (LFDMFC), based on solid polymer electrolyte membrane, is reported. Two flow cell designs, one with a parallel flow channel arrangement and the other with a spot design of flow bed, are used. The structure of the DMFC comprises a composite of two porous electrocatalytic electrodes; Pt–Ru–carbon catalyst anode and Pt–carbon catalyst cathode, on either side of a solid polymer electrolyte (SPE) membrane. The performance of three Pt–Ru catalysts is compared. The influence of the degree of Teflon loading on the electrode structure is also reported. The effect of the following parameters: cell temperature, oxygen gas or air pressure, methanol liquid flow rate and methanol concentration on the power performance is described.     

Development and electrochemical studies of gas diffusion electrodes for polymer electrolyte fuel cells

Electrochemical studies on low catalyst loading gas diffusion electrodes for polymer electrolyte fuel cells are reported. The best performance is obtained with an electrode formed from 20 wt% Pt/C, 0.4 mg Pt cm^–2 and 1.1 mg Nafion^® cm^–2 in the catalyst layer and 15% PTFE in a diffusion layer of 50 µm thickness, for both the cathode and the anode. However, it is also observed that the platinum requirement can be diminished to values close to 0.2 mg Pt cm^–2 in the cathode and 0.1 mg pt cm^–2 in the anode, without appreciably affecting the good characteristics of the fuel cell response. The experimental fuel cell data were analysed using theoretical models of the electrode structure and of the fuel cell system. It is seen that most of the electrode systems present limiting currents and some also show linear diffusion components arising from diffusion limitations in the gas channels and/or in the thin film of electrolyte covering the catalyst particles.     

Optimization of platinum dispersion in Pt–PEM electrodes: application to the electrooxidation of ethanol

Nafion® can be used as a solid polymer electrolyte in a PEM fuel cell. Direct platinization of the membrane was realized by chemical reduction of a platinum compound. The platinization procedure was modified to enhance the roughness factor and thus to improve the electrocatalytic activity towards ethanol electrooxidation. The Pt–PEM electrodes were characterized by TEM, atomic absorption analysis, cyclic voltammetry and their polarization curves for ethanol electrooxidation.     

Influence of preparation process of MEA with mesocarbon microbeads supported Pt–Ru catalysts on methanol electrooxidation

The effects of mesocarbon microbeads support for platinum–ruthenium (Pt–Ru) catalysts on anode performance of the direct methanol fuel cell (DMFC) were investigated. Polarization characteristics of the anode electrode were low due to the fast rate of mass transport in the electrode. The effects of the Nafion^® content in the catalyst, the MEA hot press condition, the cell operation temperature and methanol concentration on the polarization curves of the anode were also investigated.     

Radiation-grafted membrane/electrode assemblies with improved interface

Recent progress is reported in preparing membrane/electrode assemblies for polymer electrolyte fuel cells based on radiation-grafted FEP-g-poly(styrenesulfonic acid) membranes. MEAs with an improved interface between the membrane and commercially available gas diffusion electrodes were obtained by Nafion®-coating of the membrane and hot-pressing. These improved MEAs showed both, performance data comparable to those of MEAs based on Nafion® 112 and an operation lifetime in H₂/O₂ fuel cells of more than 2000 h at 60 °C and 500 mA cm⁻² current density.     

自呼吸式直接甲醇燃料电池性能及其传质特性

针对有效面积为1 cm2的自呼吸式直接甲醇燃料电池（direct methanol fuel cell,DMFC）单电池,阳极采用燃料罐供液,将阴极侧集流体和夹具设计为一体式结构,并用自制的七合一膜电极组件对其进行测试,讨论了催化剂类型、扩散层材料、集流体结构等因素对其性能的影响,分析了电池内部的传质特性,优化了电池特别是其在中高电流密度条件下的性能。实验结果表明：采用Pt黑、Pt-Ru黑催化剂制作的自呼吸式DMFC能强化反应物的传质;采用碳布制作的膜电极更倾向于获得更高的极限电流密度;低电流密度时,因甲醇渗透电池电压随着甲醇浓度的增加而降低,但在中高电流密度下,电池性能随甲醇浓度的增大先升高后降低;平行集流体有利于阴阳极生成物的排出和反应物的传质,因此易获得较高的电池性能。     

Electrochemical reduction of benzaldehyde using Pt-Pb/Nafion® as electrode

The electrochemical reduction of benzaldehyde using Pt-Pb/Nafion® as electrode without supporting electrolyte in the liquid organic phase was investigated. A novel Pt-Pb/Nafion® electrode was prepared for the electrolysis of the organic compound in this solid polymer electrolyte (SPEO) system. A reaction mechanism is proposed. No benzyl alcohol was produced using fresh Nafion® as electrode. The selectivity of benzyl alcohol using Pt-Pb/Nafion® as an electrode was almost 100% and only a trace of hydrobenzoin byproduct was found in the catholyte. The optimum faradic yield of benzyl alcohol was 18.70 g F^–1. The primary factors affecting the current efficiency or faradic yield of the cathodic reduction of benzaldehyde to benzyl alcohol were cell voltage, solvent and temperature. The use of a Pt-Pb/Nafion® electrode in a SPE® system for the electrochemical reduction of benzaldehyde was found to be a feasible technique.     

Direct methanol alkaline fuel cells with catalysed anion exchange membrane electrodes

Membrane electrodes prepared by chemical deposition of platinum directly onto the anion exchange membrane electrolyte were tested in direct methanol alkaline fuel cells. Data on the cell voltage against current density performance and anode potentials are reported. The relatively low fuel cell performance was probably due to the low active surface area of Pt deposits on the membrane comparing to other membrane electrode assembly (MEA) fabrication methods. However, the catalysed membrane electrode showed good performance for oxygen reduction. A reduction in cell internal resistance was also obtained for the catalysed membrane electrode. By combining the catalysed membrane electrodes with a catalysed mesh, maximum current density of 98 mA cm^–2 and peak power density of 18 mW cm^–2 were achieved.     

Accelerated durability test of DMFC electrodes by electrochemical potential cycling

Durability of direct methanol fuel cell electrodes was evaluated by electrochemical potential cycling and we observed the degradation phenomena during the performance decay. An individual potential measurement of anode and cathode with built-in reversible hydrogen electrode revealed that the anode and cathode performance contributions are almost of the same order of magnitude to the entire performance loss, although the anode degradation is relatively bigger, due to the dominating effect of ruthenium dissolution, corresponding loss of electrocatalytic activity. On the contrary, it was apparent that the electrochemical active surface area of Pt cathode decreased significantly with potential cycling under methanol crossover condition, which is not clearly reflected on the performance loss due to the initial decrease of interfacial resistance between membrane and cathode catalyst layer. Impedance studies could reinforce the current–voltage polarization by more comprehensive information.     

Direct Methanol Fuel Cells Using Thermally Catalysed Ti Mesh

Characterisation of a direct methanol fuel cell using an anode fabricated by thermal decomposition from Pt–Ru chloro-complex on Ti mesh is described. The polarisation characteristic of the resultant membrane electrode assembly is compared with that of a conventional MEA with an anode, consisting of a catalyst layer, a microporous layer and a wet-proof-treated carbon paper. Electrode characterisation was carried out using XRD, SEM and EDX analyses. In 1 m methanol solution, the MEA with the catalysed Ti mesh anode gave a power performance comparable with that of the conventional anode at 90 °C. However, in 0.5 m methanol solution the former showed much higher power density than the latter, indicating high utilisation of methanol fuel.     

Reforming methanol to electricity in a high temperature PEM fuel cell

In this paper we demonstrate for the first time a compact power unit, where a methanol reforming catalyst is incorporated into the anode of a PEMFC. The proposed internal reforming methanol fuel cell (IRMFC) mainly comprises: (i) a H₃PO₄-imbibed polymer electrolyte based on aromatic polyethers bearing pyridine units, able to operate at 200 °C and (ii) a 200 °C active and with zero CO emissions Cu–Mn–O methanol reforming catalyst supported on copper foam. Methanol is being reformed inside the anode compartment of the fuel cell at 200 °C producing H₂, which is readily oxidized at the anode to produce electricity. The IRMFC showed promising electrochemical behavior and no signs of performance degradation for more than 72 h.     

An oxygen electrode for air-consuming proton exchange membrane fuel cells for transportation applications

Electrodes for air-driven PEMFCs for transport applications have been developed. The structure of the electrodes has been specifically adapted to run with air as oxidant under near atmospheric pressure; such electrodes can be manufactured using conventional industrial methods and be easily scaled up. The technology has been demonstrated on a 50 cm² electrode area, assembled together with a Nafion® 117 membrane. Electrodes with different platinum loading, namely 0.4 and 0.2 mg Pt cm^–2, have been the subject of long duration tests which show a slow degradation of the cell performance. With air as oxidant at 180 kPa absolute pressure, 80°C as cell temperature and Nafion® 117 as membrane, a power density of 350 mW cm^–2 has been obtained.     

Investigation of direct methanol fuel cell performance of sulfonated polyimide membrane

Sulfonated polyimide (SPI) membranes have been evaluated as electrolyte membranes in direct methanol fuel cells (DMFCs). The membrane-electrode assembly (MEA) was made by hot-pressing the membrane, an anode and a cathode, catalyzed with PtRu/CB (PtRu dispersed on carbon black) and Pt/CB bound with Nafion^® ionomer, respectively. The performance of the cell based on SPI was compared with that of Nafion^® 112 in various operation conditions such as cell temperature (T_cell), cathode relative humidity (RH), and methanol concentration (C_MeOH). The methanol crossover at the cell based on SPI was a half of Nafion^® 112, resulting in the improved cell efficiency. Advantage of the use of SPI became much distinctive from the conventional Nafion^® 112 when the DMFC was operated at a higher T_cell or a higher C_MeOH.     

A novel solid state battery based on a polymer proton conductor: poly(propargyl alcohol) doped with perchloric acid

A battery was constructed by including a polymer proton conductor, poly(propargyl alcohol) doped with perchloric acid, between electrodes of magnesium and gold. The characteristics of the cell, showing an open circuit voltage of 2.0–2.2V, were studied as the function of the relative humidity. It was found that the system behaves as a fuel cell and that the discharge current of the battery is due to magnesium oxidation at the anode and proton reduction at the cathode.     

Electrochemical reduction of nitrates and nitrites in alkaline nuclear waste solutions

Sodium nitrate and nitrite are major components of alkaline nuclear waste streams and contribute to environmental release hazards. The electrochemical reduction of these materials to gaseous products has been studied in a synthetic waste mixture. The effects of electrode materials, cell design, and other experimental parameters have been investigated. Lead was found to be the best cathode material in terms of current efficiency for the reduction of nitrate and nitrite in the synthetic mix. The current efficiency for nitrite and nitrate removal is improved in divided cells due to the elimination of anodic oxidation of nitrite. Operation of the divided cells at high current densities (300–600 mA cm^–2) and high temperatures (80°C) provides more efficient reduction of nitrite and nitrate. Nearly complete reduction of nitrite and nitrate to nitrogen, ammonia, or nitrous oxide was demonstrated in 1000 h tests in a divided laboratory electrochemical flow cell using a lead cathode, Nafion® 417 cation exchange membrane, and oxygen evolving DSA® or platinum clad niobium anode at a current density of 500 mA cm^–2 and a temperature of 70° C. Greater than 99% of the nitrite and nitrate was removed from the synthetic waste mix batch in the 1000 h tests at an overall destruction efficiency of 55%. The process developed shows promise for treating large volumes of waste.