Electronic configuration of single ruthenium atom immobilized in urchin-like tungsten trioxide towards hydrazine oxidation-assisted hydrogen evolution under wide pH media

Replacing sluggish oxygen evolution reaction (OER) by hydrazine oxidation reaction (HzOR) is an energy-saving approach to assist alkaline overall water splitting (OWS). However, it is still at the infant stage as the unsatisfactory of the design strategies for bifunctional catalysts toward both HzOR and hydrogen evolution, which leads to high working potential compared to the theoretical value. Here, for the first time, we report a galvanostatic immobilization of ruthenium single atoms (Ru SAs) into the oxygen vacancy of urchin-like tungsten trioxide (VoWO3) and show low overpotentials of 17, 34, and 64 mV at -10 mA cm-2 under acid, alkaline, and neutral H2 evolution, respectively. As an efficient bifunctional catalyst, the Vo-WO3/Ru SAs is firstly introduced to HzOR and achieves low working potential of -58 mV at 10 mA cm-2. The HzOR-assisted OWS also delivers an ultralow cell voltage of only 25 mV at 10 mA cm-2 in alkaline medium, which is far beyond the platinum and most of the state-of-the-art catalysts. Additionally, this coupled system can also be well performed under neutral condition, realizing a cell voltage of only 137 mV at 10 mA cm-2. The excellent pH-universal HzOR-assisted OWS activity is attributed to the particular electronic configuration between Ru SAs and WO3, the immobilization of Ru SAs in WO3 could induce electron redistribution and optimize free energy of hydrogen adsorption in hydrogen evolution, while the isolation of Ru SAs also leads to the electropositivity of W sites and tends to accelerate the oxidation of hydrazine.