A novel self-activation strategy for designing oxygen vacancies-rich nickel ferrite and cobalt ferrite microspheres with large specific surface area for overall water splitting

Abstract

Nickel ferrite (NFO) and cobalt ferrite (CFO) have been explored as promising electrocatalysts for overall water splitting in virtue of unique characteristics. However, the poor intrinsic conductivity and the limited active sites of NFO and CFO give rise to sluggish charge transfer dynamics. It is the general approach that the target products implemented as shell are tightly wrapped on the sacrificial core of silicon dioxide (SiO2) to design the hollow/porous electrode materials, while employing SiO2 as sacrificial shell could be a novel method to improve the specific surface area (SSA) of NFO and CFO. Herein, the porous nickel ferrite (P–NFO (VO)) and cobalt ferrite (P-CFO (VO)) microspheres with rich oxygen vacancies and enhanced SSA are reported through the novel self-activation treatment along with reduction process. The simultaneous formation of rich pore channels and oxygen vacancies could expose numerous active sites, optimize electronic configuration, and boost charge transfer. As expected, the elaborately designed P–NFO (VO) and P-CFO (VO) microspheres achieve excellent achievement for HER with low overpotentials (102.9 and 100.7 mV) and relatively small Tafel slopes (45.2 and 60.1 mV/dec), respectively. Beyond that, P–NFO (VO) and P-CFO (VO) microspheres deliver favorable overpotentials of 336.3 and 384.2 mV at 10 mA/cm2 for OER, respectively, which is highly considerable to transition metal oxide-based electrocatalysts. Overall, the versatile strategy could be employed to construct other transition metal oxides with superior electrochemical properties.