Phosphoric acid passivation layer-induced sacrificial template effect for constructing S/P-modified self-supported NiFe catalysts with enhanced OER performance

Abstract

The co-doping of sulfur (S) and phosphorus (P) into mainstream NiFe catalysts can electronically modulate Ni (or Fe) sites, thus kinetically augmenting the alkaline oxygen evolution reaction (OER) more prominently than unitary modifications. However, achieving this objective via an industrially compatible synthetic route remains extremely challenging. Herein, an advantageous sacrificial template effect based on a phosphoric acid passivation layer can be easily realized, via concise one-step binary molten salt method, enabling the construction of S/P co-decorated self-supported NiFe catalysts with superior OER performance. The preferred pre-formed phosphoric acid passivation layer on the surface of a commercial NiFe foam (NFF) can effectively prevent its over-corrosion by sulphur salts and simultaneously promote S doping. This interesting process ultimately produced an integrated electrode with OER-conductive features, such as a tuned valence state, enriched oxygen vacancies, ample crystalline-amorphous boundaries, copious pores, and strong material-substrate binding. The as-synthesized electrode can deliver an ultra-low OER overpotential of 157.6 mV at a current density of 10 mA cm⁻² and ultralong stability of 1400 h to maintain an industrial-level current of 1 A cm⁻², outperforming its recent counterparts. The results of the isotope, TMA⁺ probe and pH-dependent measurements further demonstrate that S/P co-doping profoundly alters proton exchange performance, thereby altering the OER mechanism and activity. This sacrificial template effect induced by the phosphoric acid passivation layer may be extended to develop other binder-free transition metal compounds for broader electrocatalytic fields.