Development of highly active, durable, and low-cost bifunctional electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is vital to efficient and economical production of hydrogen. As a promising family of electrocatalysts, many perovskite oxides have demonstrated remarkable activities for both OER and HER under various conditions. Here we report an alternative strategy to dramatically enhance the catalytic activity of La0.8Sr0.2Cr0.69Ni0.31O3-delta(LSCN) for overall water electrolysis by surface modification and interface engineering. Exsolution of discrete Ni2P nanoparticles from LSCN, induced by a partial reduction and subsequent phosphidization, creates a unique surface with LSCN/Ni2P interfaces, which enhanced the intrinsic OER activity by similar to 6.2 times and mass activity by similar to 10.2 times. The HER activity and durability are simultaneously enhanced as well. When used as the electrocatalyst in a symmetrical two-electrode water electrolyzer, a constant cell voltage of similar to 1.70 V (vs. Reversible hydrogen electrode, RHE) is observed to sustain a water splitting current density of 10 mA cm(-2) for a continuous operation of 14 h, achieving much better performance than a state-of-the-art Pt/C(-)//IrO2(+) electrolyzer. The bifunctional electrocatalyst has potential to be a cost-effective alternative to precious metal-based electrocatalysts in commercial water splitting systems. Further, the protocol developed in this work provides a new strategy to optimize bifunctional OER and HER activities of perovskite oxides, and broadens our horizons in rational design of heterogeneous electrocatalysts for other applications. (C) 2019 Elsevier Ltd. All rights reserved.