Back to black: utilizing unsupported Pt for thin cathodes in PFSA-free PEM fuel cells

Abstract

In hydrocarbon-based proton exchange membrane fuel cells, cathode catalyst layers (CLs) made from fluorine-free, sulfonated polyphenylenes (e.g., Pemion®) face challenges in balancing sufficient gas transport with low protonic resistance – a tradeoff that is especially pronounced at application-relevant low humidity operation. Here, we address this issue by utilizing unsupported Pt, i.e., platinum black (PtB), as the electrocatalyst to reach very thin CLs (<2.5 μm). When compared to CLs with carbon-supported platinum (Pt/C), evaluation at the same roughness factor (rf) reveals a performance increase from 180 to 420 mA cm⁻² at 0.75 V, 50% RH and 95 °C, which is the highest reported performance for a fuel cell with hydrocarbon membrane and CLs and on par with perfluorosulfonic acid reference cells. Accelerated Pt dissolution tests reveal a fast initial rf loss within the first 100 potential cycles for PtB compared to Pt/C (15% vs. 4%), but virtual identical after 30 000 cycles.