Johnson Matthey Technology Review - Volume 71, Issue 1, 2027

Photocatalytic overall water splitting (POWS) is a developing method of green hydrogen production that utilises light as an energy source. Lanthanide tantalum perovskite oxynitrides (LnTaON2, Ln = lanthanide) are promising photocatalyst candidates as their valence and conduction band positions are suitable for POWS and their small bandgaps (1.8–2.4 eV) allow for utilisation of visible light. For lanthanides other than lanthanum, LnTaON2 perovskites remain underexplored for photocatalytic water splitting, with little work undertaken to optimise their photocatalytic activity and efficiency. In contrast, many successful synthetic variations have been explored to improve the photocatalytic activity of LaTaON2, including solid solution formation, morphology control and heterojunction formation. An overview of current work into non-lanthanum LnTaON2 photocatalysts is provided, along with the successful strategies utilised to improve the photocatalytic performance of LaTaON2, providing a toolbox of techniques to apply to non-lanthanum LnTaON2 photocatalysts to improve their photocatalytic performance in the future.

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.