In Situ Unraveling Surface Reconstruction of Ni-CoP Nanowire for Excellent Alkaline Water Electrolysis

The surface reconstruction behavior of transition metal phosphides precursors is considered as an important method to prepare efficient oxygen evolution catalysts, but there are still significant challenges in guiding catalyst design at the atomic scale. Here, the CoP nanowire with excellent water splitting performance and stability is used as a catalytic model to study the reconstruction process. Obvious double redox signals and valence evolution behavior of the Co site are observed, corresponding to Co²⁺/Co³⁺ and Co³⁺/Co⁴⁺ caused by auto-oxidation process. Importantly, the in situ Raman spectrum exhibits the vibration signal of Co–OH in the non-Faradaic potential interval for oxygen evolution reaction, which is considered the initial step in reconstruction process. Density functional theory and ab initio molecular dynamics are used to elucidate this process at the atomic scale: First, OH⁻ exhibits a lower adsorption energy barrier and proton desorption energy barrier at the configuration surface, which proposes the formation of a single oxygen (–O) group. Under a higher –O group coverage, the Co–P bond is destroyed along with the PO_x groups. Subsequently, lower P vacancy formation energy confirm that the Ni-CoP configuration can fast transform into a highly active phase. Based on the optimized reconstruction behavior and rate-limiting barrier, the Ni-CoP nanowire exhibit an excellent overpotential of 1.59 V at 10 mA cm⁻² for overall water splitting, which demonstrates low degradation (2.62%) during the 100 mA cm⁻² for 100 h. This work provide systematic insights into the atomic-level reconstruction mechanism of transition metal phosphides, which benefit further design of water splitting catalysts.