Platinum counter electrode contamination in oxygen reduction reaction measurements

The transition to non-platinum group metal (PGM) electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs) is central to achieving sustainable and cost-effective energy conversion. However, the continued widespread use of platinum counter electrodes in electrochemical testing introduces a critical artefact, namely, platinum dissolution, migration through the electrolyte and redeposition onto the working electrode. This potentially skews performance metrics and undermines claims of ‘platinum-free’ sustained ORR activity. This study systematically investigates this issue using a model nitrogen-doped carbon electrocatalyst with inherently low catalytic activity, allowing facile observation of small performance improvements that may be difficult to separate in high-performance catalysts. Platinum wire and graphite rod counter electrodes are compared under load cycling and start-stop conditions in both acidic and alkaline media over 60,000 potential cycles. We demonstrate that platinum contamination from the counter electrode significantly enhances ORR activity and slows performance degradation, effects which are absent when a graphite counter electrode is used. Transmission electron microscopy (TEM) confirms platinum electrodeposition on the working electrode. These findings challenge prevailing experimental protocols and establish the graphite counter electrode as essential for accurate benchmarking of non-PGM catalysts. The work delivers a clear methodological clarification with broad implications for electrocatalyst development and validation.