Constructing Ni2P/CoP heterojunction with stable built-in electric field to boost overall water splitting at industrial current density

Abstract

Constructing a heterojunction with a robust built-in electric field (BIEF) for electrocatalytic water splitting remains a formidable challenge, resulting from component instability during the electrocatalysis process that prevents the interface electron from being continuously optimized. Herein, based on a ingenious design of the structure, the issues is dresses by fabricating a Ni₂P/CoP-NF heterojunction through a simple two-step process. As an oxygen evolution reaction (OER) electrocatalyst, it demonstrates low overpotentials of 238 mV, 278 mV, and 347 mV at 50, 100, and 500 mA·cm⁻², respectively, and also demonstrates excellent hydrogen evolution reaction (HER) performance in the same electolyte. DFT calculation and experimental results reveal that the BIEF in the Ni₂P/CoP-NF promotes Co-O transformation into active site CoOOH in OER, while Co(OH)₂, acting as the active site for HER, binds readily with H₂O for effective H* formation, enhancing overall water-splitting activity. The Ni₂P structure remains stable in the whole electrocatalysis process, acting solely as an electron pump to continuously optimize the electronic configuration of CoOOH and Co(OH)₂ at the interface, allowing Ni₂P/CoP-NF to achieve durable, high bifunctional activity, maintaining stability for 300 h at 500 mA cm⁻². This work offers an effective approach to addressing the challenge of continuous interface electron optimization impeded by the structural instability of heterojunction components for efficient, stable water-splitting at industrialcurrent density.