Ir nanoparticles with ultrahigh dispersion as oxygen evolution reaction (OER) catalysts: synthesis and activity benchmarking

In this work, we present a facile and straightforward approach to synthesize, activate and benchmark small, i.e. 1.6 nm in diameter, Ir nanoparticles (NP) as oxygen evolution reaction (OER) catalysts. It is shown that the Ir NP, although oxidized after synthesis and drying, can be electrochemically reduced allowing determination of the electrochemically active surface area by CO stripping. Subsequently, an activation protocol is applied forming catalytically active Ir-oxide NP. This oxide formation is shown to be largely irreversible. It is then demonstrated that the activated Ir NP synthesized via our recently introduced colloidal method exhibit extremely high OER activities when normalized to their Ir mass. These high OER activities are related to superior dispersion as compared to state-of-the-art OER catalysts reported in the literature.