Rationally-Constructed Porous Nanosheet Ni₂P–Ni₅P₄ Heterostructures for Robust Oxygen Evolution Electrode

The development of superior non-noble-metal-based oxygen evolution reaction (OER) electrocatalysts is essential for large-scale hydrogen production. In this study, an integrated porous nanosheet Ni₂P-Ni₅P₄ heterostructures were designed as an excellent OER electrocatalyst. The synthesized heterostructures demonstrated notable activity, achieving a small overpotential of 260 mV to sustain a typical 10 mA cm^-2 current density, along with exceptional durability over 2000 CV cycles. The distinctive porous nanosheet structure enhances the exposure of active sites and improves mass transport efficiency. Density functional theory (DFT) calculations revealed that the <i>d</i>-band center of active Ni sites was shifted downward, reducing the adsorption strength of critical oxygen-containing intermediates (*O, *OH, and *OOH) in the Ni₂P-Ni₅P₄ heterostructures. This modification lowered the reaction barrier for the rate-determining step (RDS) involving the transformation from *O to *OOH, thereby boosting inherent OER activity. Additionally, partial electron localization in combination with the RDS *O intermediate was observed by electron localization functions (ELFs) in Ni₂P-Ni₅P_4, weakening the overall interaction. Further integrated crystal orbital Hamiltonian population calculations confirmed a reduced Ni-O net bonding energy of 0.69 eV for the adsorbed *O compared to that of Ni₂P (1.49 eV) and Ni₅P₄ (1.12 eV) aligning with the DFT and ELF findings. These results provide a promising approach and valuable guidance for the design of cost-effective OER electrocatalysts suitable for energy storage applications, including metal-air cells and water oxidation processes.