Abstract
The effect of the ionomer to carbon (I/C) ratio on the performance of single cell polymer electrolyte fuel cells is investigated for three different types of non-precious metal cathodic catalysts. Polarisation curves as well as impedance spectra are recorded at different potentials in the presence of argon or oxygen at the cathode and hydrogen at the anode. It is found that a optimised ionomer content is a key factor for improving the performance of the catalyst. Non-optimal ionomer loading can be assessed by two different factors from the impedance spectra. Hence this observation could be used as a diagnostic element to determine the ideal ionomer content and distribution in newly developed catalyst-electrodes. An electrode morphology based on the presence of inhomogeneous resistance distribution within the porous structure is suggested to explain the observed phenomena. The back-pressure and relative humidity effect on this feature is also investigated and supports the above hypothesis. We give a simple flowchart to aid optimisation of electrodes with the minimum number of trials.
Highlights
Commercialisation of low temperature fuel cells requires significant cost reductions [1]
While the activity of precious metal catalysts is localized on micro- and/or nanoparticles that are attached to the carbon support, the activity in non-precious metal catalysts is believed to be highly dispersed within the structure itself or situated on the opening of micropores [8]
Experiments were made in the presence and absence of reactant in order to gain deeper insight into the operation of the fuel cell and to determine whether the ionomer content is too high or too low by Electrochemical Impedance Spectroscopy (EIS). This analysis opens the way to a understanding of the behaviour of non-precious metal catalyst layers, which is fundamental for the further development of alternative oxygen reduction reaction catalysts
Summary
Commercialisation of low temperature fuel cells requires significant cost reductions [1]. While the activity of precious metal catalysts is localized on micro- and/or nanoparticles that are attached to the carbon support, the activity in non-precious metal catalysts is believed to be highly dispersed within the structure itself or situated on the opening of micropores [8] This has tremendous impact on the requirements for proton and gas transport within the catalyst layer. This analysis opens the way to a understanding of the behaviour of non-precious metal catalyst layers, which is fundamental for the further development of alternative oxygen reduction reaction catalysts. It helps to develop a simple strategy for the estimation of the optimal I/C ratio for a newly prepared NPMC accelerating developments in this field
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