(Invited Plenary) Electrocatalysis in PEFCs –  limitations in the Performance of the Hydrogen Oxidation and Oxygen Reduction Reactions

Monday, 2 October 2017: 14:40
National Harbor 2/3 (Gaylord National Resort and Convention Center)
A. Kucernak (Imperial College London)
An alternative approach to the rotating disk electrode (RDE) for characterising fuel cell electrocatalysts has been recently demonstrated[1, 2]. The approach combines high mass transport with a flat, uniform, and homogeneous catalyst deposition process, well suited for studying intrinsic catalyst properties at realistic operating conditions of a polymer electrolyte fuel cell (PEFC). Uniform catalyst layers were produced with loadings as low as 0.16 μgPt cm‑2 and thicknesses as low as 200 nm, Figure 1. Such ultra thin catalyst layers are considered advantageous to minimize internal resistances and mass transport limitations leading to very high performance at low platinum loadings. Modelling of the associated diffusion field suggests that such high performance is enabled by fast lateral diffusion within the electrode. The electrodes operate over a wide potential range with insignificant mass transport losses, allowing the study of the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) at high overpotentials. For the HOR, geometric current densities as high as 5.7 A cm‑2Geo were experimentally achieved at a loading of 10.15 μgPt cm-2 at room temperature (561 A mgPt-1), which is three orders of magnitude higher than current densities achievable with the RDE. These currents correspond to a specific current densities of 600 ± 60 mA cm‑2Spec, although this maximum appears to be related - to the hydrogen adsorption process. For the ORR, electrodes produced a specific current density of 31 ± 9 mA cm‑2Spec at a potential of 0.65 V vs. RHE (28 A mg-1), Figure 2. The mass activities of Pt/C catalysts towards the ORR was found to exceed a range of literature PEFC mass activities across the entire potential range. This paper will discuss the lessons that can be learnt from these electrocatalytic studies and what they mean in terms of ultimate performance of fuel cells utilising precious metal catalysts.

[1] C.M. Zalitis, D. Kramer, J. Sharman, E. Wright, A.R. Kucernak, Pt Nano-Particle Performance for PEFC Reactions At Low Catalyst Loading and High Reactant Mass Transport, in: Polymer Electrolyte Fuel Cells 13, 2013, pp. 39-47.

[2] C.M. Zalitis, D. Kramer, A.R. Kucernak, Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport, Physical Chemistry Chemical Physics, 15 (2013) 4329-4340.