Oxygen vacancies induced low overpotentials of Ag/CeO2 for electrocatalytic evolution of oxygen and hydrogen

Abstract

Designing efficient catalysts for the evolution of hydrogen and oxygen through electrocatalytic water splitting remains an area of significant interest. Herein, we develop an Ag/CeO₂ catalyst that demonstrates a remarkable electrocatalytic performance for hydrogen and oxygen evolution through water splitting. The high catalytic activity can be attributed to the interaction between Ag and CeO₂, which increases the oxygen vacancies at the interface. This is substantiated by the results from Raman, X-ray photoelectron, electron paramagnetic resonance and photoluminescence spectroscopy. The reduced photoluminescence intensity validates the effective separation of photogenerated electron–hole pairs due to oxygen vacancies. Besides increasing the oxygen vacancies, Ag enhances light absorption and reduces the band gap of CeO₂, which is evident from a remarkable enhancement in the electrocatalytic activity of Ag/CeO₂, especially under light illumination, compared to pristine CeO₂. Notably, a drastic reduction in overpotential and an increase in current density are observed for Ag/CeO₂. For the oxygen evolution reaction, Ag/CeO₂ exhibits a reduction of 120 mV in the overpotential and an increase of 19.8 mA cm⁻² in the current density with the lowest Tafel slope of 158 mV dec⁻¹ compared to CeO₂. For the hydrogen evolution reaction, Ag/CeO₂ exhibits a reduction of 130 mV in the overpotential and an increase of 14.1 mA cm⁻² in the current density. Considering the results from characterization techniques and electrocatalytic experiments, a plausible mechanism has been proposed for the electrocatalytic performance of the catalyst. This study offers insights into defect-induced ceria-based materials for optimizing and designing effective electrocatalysts for overall water splitting.