Substrate-Involved OER Reconstruction of Self-Supported CoP Nanoflowers on Iron Foam Enables Durable Alkaline Water Splitting

Abstract

Developing cost-effective and durable electrocatalysts from earth-abundant elements is essential for sustainable hydrogen production by alkaline water electrolysis. Herein, self-supported CoP nanoflowers on iron foam (CoP/IF) are fabricated via electrodeposition followed by in situ phosphorization. Benefiting from the hierarchical nanoflower architecture and the intimate coupling between the catalyst layer and the conductive substrate, the resulting CoP/IF electrode exhibits excellent bifunctional electrocatalytic activity, requiring overpotentials of only 205 mV for the oxygen evolution reaction (OER) and 87 mV for the hydrogen evolution reaction (HER) at 10 mA cm–2. When employed as both the anode and cathode, the CoP/IF-based electrolyzer delivers 10 and 100 mA cm–2 at low cell voltages of 1.52 and 1.71 V, respectively, and sustains stable operation at 100 mA cm–2 for 1200 h with 96% activity retention. More importantly, in situ Raman spectroscopy, combined with ex situ characterizations, reveals that CoP/IF acts as an OER precatalyst and undergoes extensive substrate-involved reconstruction into a CoOOH/FeOOH active phase, rather than merely forming a shallow reconstructed surface layer. The results indicate that the iron foam substrate serves not only as a three-dimensional conductive scaffold but also as a chemical participant in active-phase generation during the OER. Density functional theory calculations demonstrate that Fe incorporation into the reconstructed CoOOH/FeOOH heterostructure modulates the electronic structure of Co sites, elevates the Co d-band center, strengthens *O adsorption, and lowers the energy barrier for the rate-determining step. This work provides a sustainable strategy for designing efficient, durable, and low-cost self-supported electrodes for practical alkaline water splitting while also highlighting the often-overlooked role of foam substrates in OER reconstruction and true active-phase generation.