Tuning Electronic Structures of Nonprecious Ternary Alloys Encapsulated in Graphene Layers for Optimizing Overall Water Splitting Activity

Abstract

Electrochemical water splitting is considered as the most promising technology for hydrogen production. Considering overall water splitting for practical applications, catalysis of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) should be performed in the same electrolyte, especially in alkaline solutions. However, designing and searching for highly active and inexpensive electrocatalysts for both OER and HER in basic media remain significant challenges. Herein, we report a facile and universal strategy for synthesizing nonprecious transition metals, binary alloys, and ternary alloys encapsulated in graphene layers by direct annealing of metal–organic frameworks. Density functional theory calculations prove that with an increase in the degree of freedom of alloys or a change in the metal proportions in FeCoNi ternary alloys, the electronic structures of materials can also be tuned intentionally by changing the number of transferred electrons between alloys and graphene. The optimal material alloys FeCo and FeCoNi exhibited remarkable catalytic performance for HER and OER in 1.0 M KOH, reaching a current density of 10 mA cm –2 at low overpotentials of 149 mV for HER and 288 mV for OER. In addition, as an overall alkaline water electrolysis, they were comparable to that of the Pt/RuO 2 couple, along with long cycling stability.