Synergistic Interfacial Engineering of Heterostructured Cobalt Phosphide Spheres/Cobalt Hydroxide Nanosheets for Overall Water Splitting

Abstract

Recently, transition metal phosphides (TMPs) have been widely explored for the hydrogen evolution reaction (HER) due to their advantaged activity. Nevertheless, the OER performance of TMPs in an alkaline medium is still unsatisfactory. Therefore, interfacial engineering of TMPs to enhance the OER performance is highly desirable. Herein, a Co(OH)₂ nanosheet coupled with a CoP sphere supported on nickel foam (NF) is developed by a simple two-step electrodeposition. The large surface area derived from stacked nanosheets and the electronic regulation induced by heterostructure can significantly enhance charge/mass transfer and expose more active sites, thus accelerating the kinetics of the reaction. In addition, the strong electronic interaction between CoP and Co(OH)₂ is conducive to the generation of a high valence cobalt center; thus, the electrocatalytic performances toward HER and OER are remarkably improved. Impressively, the optimized CoP/Co(OH)₂@NF heterostructure obtains an excellent HER and OER performance with low overpotentials of 76 and 266 mV at 10 mA cm^-2, respectively, superior to the commercial Pt/C and RuO₂. Moreover, the optimized CoP/Co(OH)₂@NF can afford the lowest cell voltage of 1.58 V to achieve 10 mA cm^-2 for alkaline overall water splitting and shows outstanding long-term stability.