Paul Leonard Adcock

Stainless steel as a bipolar plate material for solid polymer fuel cells

Stainless steel bipolar plates for the Solid Polymer Fuel Cell (SPFC) offer many advantages over conventional graphitic materials. These include relative low cost, high strength, ease of manufacture and as they can be shaped into thin sheets, significant improvement in the power/volume ratio. However, interfacial ohmic losses across the metallic bipolar plate and the Membrane Electrode Assembly (MEA), reduce the overall power output from a SPFC. Despite a large range of commercially available alloys, 316 stainless steel has traditionally been the alloy of choice for bipolar plates. A number of alternative grades of stainless steel have been evaluated in terms of the electrical resistance of their surface oxide film. This showed that ohmic losses exhibited in fuel cell performance varied depending on the elemental composition of the stainless steel alloy. Three stainless steel alloys, 310, 316 and 904L, were chosen as candidate bipolar plate materials. Increased polarisation was observed in the order 904L<310<316. This was maintained throughout an ongoing endurance test, where these cells have been run for over 3000 h without significant performance degradation. This difference in polarisation behaviour was attributed to variation in thickness of the oxide film. Analysis has shown no deleterious effect on the surface of the bipolar plate and no evidence of corrosion.

Bipolar plate materials for solid polymer fuel cells

The interfacial ohmic losses between the bipolar plate and the MEA can significantly reduce the overall power output from a SPFC. For graphitic bipolar plate materials, these losses are insignificant relative to stainless steel, where the existence of a passive film on the surface greatly reduces electrical conductivity. In this paper we have evaluated different bipolar plate materials, and present long-term fuel cell data for Poco® graphite, titanium, 316 and 310 stainless steel. The properties of the passive film on the surface of 316 and 310 stainless steel are markedly different. Although both were adequately corrosion resistant in a fuel cell environment, 310 tended to produce higher fuel cell performance and like 316, no degradation was observed after 1400 h testing. Analysis of the passive film indicated that this increased performance was related to the decreased thickness of the oxide film.

New materials for polymer electrolyte membrane fuel cell current collectors

Polymer Electrolyte Membrane Fuel cells for automotive applications need to have high power density, and be inexpensive and robust to compete effectively with the internal combustion engine. Development of membranes and new electrodes and catalysts have increased power significantly, but further improvements may be achieved by the use of new materials and construction techniques in the manufacture of the bipolar plates. To show this, a variety of materials have been fabricated into flow field plates, both metallic and graphitic, and single fuel cell tests were conducted to determine the performance of each material. Maximum power was obtained with materials which had lowest contact resistance and good electrical conductivity. The performance of the best material was characterised as a function of cell compression and flow field geometry.

The effects of battlefield contaminants on PEMFC performance

Abstract The effects of contaminants on the performance of an air breathing proton exchange membrane fuel cell (PEMFC) were investigated, by introduction into oxidant air fed to the fuel cell. The impact of the common pollutants sulphur dioxide, nitrogen dioxide, carbon monoxide, propane and benzene and the chemical warfare agents, sarin, sulphur mustard, cyanogen chloride (CNCl) and hydrogen cyanide (HCN) were assessed. At the concentrations studied, the common contaminants had either no effect on performance or caused a reversible depression. The chemical warfare agents all seriously compromised the performance of the fuel cells in an irreversible manner.

A carbon monoxide PROX reactor for PEM fuel cell automotive application

Abstract Loughborough University have designed, constructed and evaluated a compact CO preferential oxidation (PROX) reactor for PEM fuel cell applications. The reactor design is based upon the catalyst coating of high surface area heat transfer technology. Catalyst screening studies have revealed a mixed transition metal oxide promoted platinum–ruthenium formulation to be suitable for the particular reactor application i.e. acceptable CO oxidation activity and selectivity within a temperature range of 130–200°C. The CO PROX reactor design has been sized for 20 kW e PEM fuel cell applications, and is based upon 2×2 l catalyst washcoated compact fin heat exchangers. The PROX reactor has being successfully integrated and commissioned with a methanol steam reformer with reductions in fuel CO concentrations of 2.7% to

A compact CO selective oxidation reactor for solid polymer fuel cell powered vehicle application

Solid polymer fuel cells (SPFCs) are attractive as electrical power plants for vehicle applications since they offer the advantages of high efficiency, zero emissions, and mechanical robustness. Hydrogen is the ideal fuel, but is currently disadvantaged for automotive applications by the lack of refuelling infrastructure, bulky on-board storage, and safety concerns. On-board methanol reforming offers an attractive alternative due to its increased energy storage density. Since CO is always present as a by-product during the reforming reaction, it must be reduced to a level less than 20 ppm in order to avoid rapid deactivation of the platinum electro-catalyst in the fuel cells. In this paper, a compact CO selective oxidation unit based upon two coated aluminium heat exchangers, developed at Loughborough University, is reported. The geometric size of the whole unit is 4 litre and experimental results show that the selective oxidation unit can reduce the CO from up to 2% to less than 15 ppm and is suitable for a vehicle fuel cell power plant of 20 kWe.

Evaluation and modelling of a CO selective oxidation reactor for solid polymer fuel cell automotive applications

On-board methanol reforming is an attractive alternative to direct hydrogen storage for solid polymer fuel cell (SPFC) powered vehicles, due to the increased volumetric energy storage density of methanol. Unfortunately, carbon monoxide is always produced during the reforming reaction. CO rapidly de-activates the platinum electro-catalyst in the fuel cell and must be reduced to levels typically less than 20 ppm. In this paper, the development of a precious metal based catalytic CO oxidation reactor developed by the Fuel Cell Research Group at Loughborough University is reported. A simplified simulation model has also been developed, based upon measured catalyst activity and CO oxidation selectivity. Experimental results from reactor studies show that CO concentrations can be reduced from a typical steam reformer output of 7000 ppm input to ≤15 ppm in the presence of approximately 75% hydrogen. Experimental results have shown good agreement with the simulation model.

Effect of operating pressure on the system efficiency of a methane-fuelled solid polymer fuel cell power source

Abstract The energy conversion efficiency of a fuel cell is directly related to its operating voltage. In general increasing the fuel and oxidant pressure increases the cell potential. However, additional energy is required to compress the gases in order to raise the pressure, negating the efficiency gains achieved in the cells. System designers seek to balance complexity, cost and system efficiency. The overall system efficiency is highly dependent on the interaction and interconnection of the components. For a system which includes a solid polymer fuel cell (SPFC) stack, a methane fuel processor and a compressor/expander an analysis has been carried out to assess the functional relationship between the operating pressure and efficiency. For a system configuration which includes a high-temperature fuel processor and a 40-kW e stack, an 8% improvement in efficiency was predicted for the higher operating pressure (25% for 1.5 bar(a) and 33% for 4 bar(a).

Prospects for the application of fuel cells in electric vehicles

Abstract For a hybrid vehicle the use pattern has large effect on the vehicle design. If the vehicle is to be used extensively on the motorway then a continuous high power is required. For the case of a fuel cell battery hybrid vehicle this would require a large fuel cell ( > 30 kW) to meet the sustained high power demand. The current high materials and fabrication cost of most fuel cells prohibits the commercial development of such a system. Consequently if fuel cell vehicles are to enter a ‘clean car’ market, earlier rather than later, alternative configurations must be sought and compromises in terms of performance are inevitable.

Solid polymer fuel cells for pulse power delivery

Solid polymer fuel cells have been identified as suitable sources for the delivery of short duration, high power pulses. A number of membrane/electrode assemblies, cell designs and component materials have been tested under continuous load conditions to enable an optimised fuel cell to be constructed and to allow comparisons with pulsed load conditions. Each cell was subjected to pulsed loads of one second duration to identify the best cell components and the power losses associated with this regime. Best performance was obtained with low equivalent weight, thin membranes with high catalyst utilisation and optimised flow designs.