Ag-Bi₂O₃-Nanostructured Composite Electrodes toward Catalyzing Oxygen Evolution Reaction: Exploring Oxygen Evolution Reaction Kinetics in Composites from Doping to Establishing a Heterojunction

Electrochemical water splitting involving two-half chemical cell reactions is a promising approach to generate hydrogen and oxygen. Although this method is sustainable, the sluggish kinetics of the oxygen evolution reaction (OER) occurring at the anode due to a high overpotential is an issue to be addressed. Recently, various chemical and structural engineering approaches have been explored to improve the efficiency of the OER by reducing the overpotential. Among them, incorporating noble metals into the electrodes by doping or creating heterojunctions is an appealing approach to develop efficient OER electrocatalysts. Based on this principle, herein, we synthesized a bismuth-oxide (Bi₂O₃) electrocatalyst incorporated with silver nanoparticles (Ag NPs) by a facile one-step hydrothermal method to take advantage of the high conductivity of Ag NPs and the low band gap along with fast redox reaction of Bi₂O₃. With the Ag⁺ concentration in the hydrothermal precursor solution, the thickness of hydrothermally formed Bi₂O₃ nanoplates decreases, resulting in the increased electrochemical surface area (ECSA) from 71 to 300 cm². The optimal electrode, heterojunction-formed Ag-Bi₂O₃ (denoted H-Ag_1.00-Bi₂O₃), exhibits the lowest overpotential of 260 mV for the OER at a current density of 10 mA cm^-2 with an excellent durability of 77.5% after stability tests for 240 h due to the number of active sites produced by Ag doping (manifesting defects), and heterojunction established between Ag nanoparticles and Bi₂O₃ nanoplates. The approach explored in this work could be further utilized to produce other effective electrocatalysts for accelerating OER performances.