Exploring the sub-nanometre domain: Evaluating mass loading effects on platinum nanocluster catalysts fabricated via magnetron sputtering

Herein we demonstrate the use of magnetron-sputtered, low weight-loading platinum on carbon black catalysts as a pathway to reducing mass of platinum in electrolyser and fuel cell applications. In contrast to wet chemical methods, which often require multi-step syntheses involving toxic chemicals and washing post synthesis, magnetron sputtering can produce catalysts for use immediately after production. Scanning transmission electron microscope (STEM) analysis shows these bespoke catalysts possess a bimodal distribution of particle sizes, with nanoparticles approximately half the size of commercial equivalents (ca.1 vs > 2 nm) and a distinct distribution of single metal atoms, dimers and trimers. Measurement of the electrochemically active surface area (ECSA) revealed a higher surface area across all fabricated catalysts, ranging from 17 % to 51 % higher than commercial equivalents. This increased surface area provides a comparable hydrogen evolution reaction (HER) onset potential at a fraction of the platinum loading, indicating both that kinetics are not affected measurably by changes in platinum size and that the Pt particles are well dispersed across the support. In contrast, the oxygen reduction reaction (ORR) activity showed clear kinetic differences due to particle size with the onset potential varying by over 100 mV across the catalyst samples, reflecting the influence of stable platinum nanoclusters on catalytic activity. Rotating ring disc electrode (RRDE) voltammetry offered additional insight into the size and dispersion of the platinum nanoclusters across the samples, elucidating differences between them.