Dual elemental modulation in cationic and anionic sites of the multi-metal Prussian blue analogue pre-catalysts for promoted oxygen evolution reaction

Abstract

Designing advanced electrocatalysts for the oxygen evolution reaction (OER) is of great significance owing to its crucial role in facilitating the production of clean hydrogen energy via water splitting. To date, it has been widely accepted that a pre-oxidation process with the in-situ generation of the catalytically active high-valence metal sites is essential for promoting the OER behavior of most transition-metal-based OER catalysts, or more felicitously speaking, pre-catalysts. Hence, exploring such pre-catalysts with high pre-oxidation reactivity is of high promise. Herein, we proposed the dual elemental modulation in the cationic and anionic sites of the multi-metal Prussian blue analogue (PBA) pre-catalysts, resulting in promoted OER behavior benefitted from the efficient pre-oxidation ability as well as the multi-metal synergy. Detailed investigations indicate that the Co-containing multi-metallic cations and mixed FeIIICoIII cyanide anions in NiCuCoII–FeIIICoIII PBA (denoted as NiCuCoII–FeIIICoIII) are beneficial to OER catalysis owing to the high intrinsic activity guaranteed by the local Co3+ active sites as well as the optimal multi-metal synergy. After the facile pre-oxidation process, additional high-valence Ni, Cu and Fe ions can be in-situ formed and serve as the active sites, thereby resulting in significantly improved OER behavior. For example, the OER current density of NiCuCoII–FeIIICoIII exhibits 1.81 times enhancement even after 72 ​h continuous OER catalysis, and the required overpotential for 10 ​mA ​cm−2 reduces from 288 ​mV for the fresh pre-catalyst to a remarkable record of 251 ​mV after the pre-oxidation-induced activation, making the optimal PBA-based catalyst a promising candidate for efficient and durable water electrolysis.