Electrocatalytic water splitting into hydrogen and oxygen holds great promise for renewable energy conversion and usage, but its application is limited by the sluggish kinetics of the water oxidation (oxygen evolution reaction). Forming active species (metal oxide/hydroxide) on the surface of metal non-oxide compounds is proven to be an effective strategy for improving activity. In this work, O-2 plasma-assisted strategy is employed to controllably construct 4-6 nm NiFeOx amorphous layer on the surface of NiFeP. Benefiting from the synergistic effect between NiFeP and NiFeOx, large electrochemical surface area, and favorable three-dimensional hierarchical nanostructure, the resulting NiFeOx/NiFeP/NF catalyst exhibits extraordinary water oxidation performance in alkaline media. A current density of 10 mA cm(-2) is achieved at a low overpotential of 165 mV with good stability, which outperforms most of the transition-metal-based electrocatalyst reported. Density functional theory (DFT) calculations suggest that the improved electrochemical performance of NiFeOx/NiFeP can be understood as a result of the optimized electronic structure and increased active catalytic sites. This work might shed light on the design and fabrication of efficient and durable electrode materials for a variety of electrochemical applications. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.