Rational design of multi-component Fe(OH)3/Ni-NiO heterostructures bifunctional catalyst for electrochemical water splitting.

• The Fe(OH) 3 /Ni-NiO heterojunction was successfully prepared. • The Fe(OH) 3 /Ni-NiO as bifunctional catalysts showed high HER and OER activities. • The heterogeneous interface between Ni, NiO and Fe(OH) 3 promoted the HER process. Exploring economic-efficient bifunctional catalysts is critical for the production of green hydrogen through water splitting. Herein, we fabricate a novel hybrid catalyst with three-phase heterojunction (Fe(OH) 3 /Ni-NiO) via a simple electrodeposition and chemical precipitation method. Benefiting from the desirable amorphous-crystal interfaces, the electronic structure of Ni, NiO and Fe(OH) 3 is regulated, which will optimize the adsorption of H intermediates (H*) and also reduce the kinetic barrier for the hydrogen evolution reaction (HER). The optimal Fe(OH) 3 –3/Ni-NiO/CC shows superior bifunctional activity with low overpotentials of 66 mV for HER and 220 mV for OER at 10 mA cm−2 in alkaline solution, respectively, as well as remarkable durability over a period of 40 h. Besides, Fe(OH) 3 –3/Ni-NiO/CC requires 1.52 and 1.72 V to deliver 10 and 100 mA cm−2 and shows no obvious increase in current within 40 h toward overall water splitting. Experimental and theoretical results show that the HER process is promoted by the synergistic effect of electronic redistribution between Ni, NiO and Fe(OH) 3 due to the construction of three phase crystalline-amorphous heterogeneous interface. Meanwhile, Fe(OH) 3 and NiO appeared reconstruction, transforming into FeOOH and NiOOH during OER process, respectively. This work offers a simple synthesis method for designing bifunctional catalysts for water splitting. We fabricate a novel hybrid catalyst with three-phase heterojunction (Fe(OH) 3 /Ni-NiO) via a simple electrodeposition and chemical precipitation method. The optimal Fe(OH) 3 -3/Ni-NiO/CC shows superior bifunctional activity at 10 and 100 mA cm−2 with voltages of 1.52 and 1.88 V for overall water splitting and no obvious increase in current within 40 h. [Display omitted] [ABSTRACT FROM AUTHOR]