Highly reversible water splitting cell building from hierarchical 3D nickel manganese oxyphosphide nanosheets

The development of highly active and durable non-precious electrocatalysts with hierarchical nanostructures remains a key challenge in industrial applications for overall water splitting process. Herein, for the first time, a new strategy is established to fabricate hierarchical 3D nickel manganese oxyphosphide nanosheets (NiMnOP NSs) with high electroactive sites, numerous nanoporous networks, and plentiful oxygen vacancies for highly reversible water splitting application. When serving as the catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the hierarchical 3D NiMnOP catalyst entails the low overpotentials of about 195 and 290 mV, respectively, at a current density of 500 mA cm⁻² with long-term durability. Impressively, HER and OER performances of NiMnOP catalyst are highly reversible because of their interconversion characteristics of both catalytic active sites. The assembled NiMnOP||NiMnOP water splitting cell delivers a current density of 10 and 500 mA cm⁻² at cell voltages of 1.51 and 1.72 V, respectively, which is superior to state-of-art Pt-C||RuO₂ (~1.53 V at a current density of 10 mA cm⁻²). Most importantly, the water splitting cell reveals excellent reversibility of both half-reactions in water splitting process at a high current density of 100 mA cm⁻². This process can successfully overcome the electrochemical stability problems initiated by electrode depolarization throughout repeated power disconnection, where frequency fetching is expected to occur by the utilization of irregular renewable energy distributions.