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 the mainstream NiFe catalysts can electronically modulate the Ni (or Fe) sites, thus kinetically augmenting the alkaline oxygen evolution reaction (OER) more prominently than unitary modifications. However, achieving this objective via an industrial-compatible synthetic route remains extremely challenging. Herein, an advantageous sacrificial template effect based on the phosphoric acid passivation layer can be easily realized, via a concise one-step binary molten salt inspiration, enabling the construction of the S/P co-decorated self-supported NiFe catalysts for superior OER performance. The prioritized pre-formed phosphoric acid passivation layer on the surface of commercial NiFe foam (NFF) can effectively prevent its over-corrosion by the sulphur salt and simultaneously promote the S doping. This interesting process ultimately produced an integrated electrode with OER-conductive features, such as the tuned valence state, enriched oxygen vacancies, ample crystalline-amorphous boundaries, copious pores, and strong material-substrate binding. The as-synthesized electrode can deliver the 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 the recent peers. Results of 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 phosphoric acid passivation layer may be extended to develop other binder-free transition metal compounds for broader electrocatalytic fields.