Interface engineering of porous nickel-iron phosphates with enriched oxygen vacancies as an efficient bifunctional electrocatalyst for high current water splitting

The delicate design of non-precious metal-based bifunctional electrocatalysts for simultaneous oxygen/hydrogen evolution reactions is pivotal for developing green and sustainable energy sources. Here, we have fabricated a novel nickel-iron phosphate heterostructure with abundant oxygen vacancies (Fe0.86Ni0.14-POx/CC) via hydro -thermal reaction and gas-phase phosphating treatment. By appropriately adjusting the ratio of Ni/Fe, the elec-tronic structure is regulated, thereby optimizing the oxygen vacancies to form abounded electrocatalytic active centers on the catalyst surface. The obtained Fe0.86Ni0.14-POx/CC catalyst reveals low overpotentials of 247 and 125 mV for OER and HER at a current density of 10 mA cm-2, respectively. Besides, the overall water splitting electrolyzer originated from Fe0.86Ni0.14-POx/CC only requires a cell voltage of 2.01 V to deliver a current density of 500 mA cm-2 with good stability of 100 h (10 mA cm-2). Importantly, Fe0.86Ni0.14-POx/CC possess 96.9 and 97.7% Faradaic yield for the generation of H2 and O2, respectively. This work invokes new feasibility for developing robust and cost-effective phosphate catalysts for electrochemical overall water splitting.