Engineering Amorphous Nickel Iron Oxyphosphide as a Highly Efficient Electrocatalyst toward Overall Water Splitting

Searching highly efficient earth-abundant materials with bifunctional properties for electrocatalytic water splitting is an urgent task to develop hydrogen (H2) energy resource. Herein, nickel iron oxyphosphide (NiFeOP) with an amorphous structure is constructed synchronously via a facile phosphidation treatment on NiFe layered double hydroxide (LDH) nanoflakes. The incorporated P heteroatoms greatly alter the surface atom composition and configuration, thus resulting in an amorphous structure containing abundant defects and active states. Consequently, the as-obtained NiFeOP manifests prominent electrocatalytic performance for the oxygen evolution reaction (OER) under the alkaline condition with a small Tafel slope (43.10 mV dec–1) and a low overpotential (310 mV) to achieve a current density of 10 mA cm–2. Meanwhile, NiFeOP is also active for the hydrogen evolution reaction and therefore shows the enhanced full water splitting activity in comparison with pristine NiFe LDH. Operando electrochemical impedance spectroscopy and activation energy measurements demonstrate that amorphous NiFeOP undergoes fast charge-transfer kinetics and decreased activation energy, leading to superior OER activity. This study provides a novel strategy for the rational engineering of promising amorphous NiFe-based electrocatalysts toward water electrolysis applications.