Hierarchical heterostructure consists of Al3+doped NiFe2O4nanocubes on NiCo2O4nanosheets for efficient electrocatalytic water splitting

Abstract

Spinels are advanced electrocatalysts for oxygen evolution reaction (OER) due to oxophilic properties, however, their research in the field of hydrogen evolution reaction (HER) or overall water splitting (OWS) is rarely reported. In this paper, a hierarchical heterostructure electrocatalyst consists of Al3+ doped NiFe2O4 nanocubes on NiCo2O4 nanosheet arrays (A-NCO@NFO/NF) was successfully prepared for electrocatalytic OWS. The preparing strategy is conducting [Fe(CN)6]3- anion exchange and Al3+ cation doping of NiCo(OH)x grown on nickel foam (NF) accompanied by subsequent air calcination. HRTEM confirmed that the successful formation of NCO/NFO heterointerface and the incorporation of Al3+ into the lattices of NCO and NFO. XPS indicated that the NCO/NFO heterojunction promotes the electron transfer from Ni to Fe, which is favorable for the adsorption of H+ during the HER process, and the Al3+ facilitates the electron transfer from Fe to Co, which is favorable for the formation of CoOOH active species during the OER process. The HER and OER overpotentials of the electrocatalyst are only 178 mV and 159 mV, respectively, and a current density of 10 mA cm-2 can be achieved with only 1.61 V applied during the OWS process, also with excellent stability for 25 h. This study provides a new idea for designing spinel-based green composite electrocatalysts.