Low Cost Electrode Development And Performance In Ballard Advanced Stack Hardware

G.A.Hards, T.R.Ralph Johnson Matihey Technology Centre, Blounts Court, Sonning Common, Reading, U.K.

D.P. Wilkinson, S.A.Campbell Ballard Power Systems, Bumaby, B.C. Canada.

Introduction

Cost reduction is a critical requirement for the widespread commercial application of proton exchange membrane fuel cell (PEMFC) technology. Significant stack cost savings are available through materials cost reductions and the development of low cost, high volume, manufacturing processes. This paper summarises progress made by Ballard Power Systems and Johnson Matthey in the development of lower cost stack component technology. Single cell performance in Ballard Mark V hardware, of membrane electrode assemblies (MEAs) employing volume manufactured electrodes with catalyst loadings below 1.0 mgPtcm"2, are comparable to current stack MEAs comprising unsupported platinum based catalysts with loadings of 8.0 mgPtcm'2. In the advanced stack hardware, under development for motive and utility applications, the low cost MEAs exhibit high performance and minimal voltage decays after over 3,000 hours of stack operation. Cell to cell reproducibility is excellent, highlighting the high consistency of product available from the manufacturing processes. The MEAs represent a significant progress in the commercialisation of PEMFC systems. Incorporation of the technology in commercial prototype stacks is underway.

MEA Fabrication

A high volume electrode manufacturing process has been developed based on printing technology. The process was selected based on its ability to meet several key criteria, including low capital investment, scaleability with increasing demand, low unit cost, flexibility to accommodate a wide range of formulations and structures, high yield and high product reproducibility. A pilot plant facility established at Johnson Matthey has the capability of meeting demand over the coming years as the PEMFC enters commercial production. The low precious metal loading electrodes comprise Pt/Ru catalyst based anodes (50:50 atomic ratio Pt:Ru), and pure Pt catalyst based cathodes, supported on Cabot Vulcan XC72R carbon black. To maximise the catalyst surface area available for reaction in the printed electrodes a soluble form of the proton conducting electrolyte is incorporated into the active catalyst region in a fashion that allows for mass production. Anode catalyst loadings from 0.1 - 0.4 mgPtcm"2 and cathodes from 0.2 - 0.7 mgPtcm'2 have been routinely manufactured.

Beginning of Life Performance

Figure 1 compares the performance of a low cataljst loading MEA (0.6 mgPtcm'2) and a higher loading unsupported platinum black MEA (8.0 mgPtcm"2). The beginning of life (BOL) data is from a standard Ballard Mark V single cell of 240.2 cm2 active area, operating at 80°C on hydrogen/air at 30/30 psig and 1.5/2.0 stoichiometry. The membrane electrolyte was the Dow XUS-13204.10 experimental material. The BOL performance of the lower cost MEA is equivalent to the higher catalyst loading MEA employed in current demonstration Mark V stacks. There are no issues associated with the combination of carbon supported catalyst based anodes and cathodes in this cell hardware. At a cell voltage of 0.65 V, the low loading MEA generates 0.8 Acm"2. This translates to a much reduced plalinum requirement of ca. 1.2 gPtkW"1 , which is compatible with the cost targets for PEMFC applications in both stationary power generation and heavy duty transportation such as transit buses.

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