Determining kinetics of H2O2 evolution from photoelectrochemical water oxidation

Photoelectrochemical water oxidation to generate H2O2 is a clean and promising method. Its performance is strongly dependent on electrolyte species, in which the Faradaic efficiency is considerably promoted by HCO3− anion. The kinetic mechanism is under debate, which is highly desired but challenging. Herein, we reveal the charge dynamics and reaction kinetics in the H2O2 evolution from photoelectrochemical water oxidation by time-resolved spectroscopic techniques. The H2O2 evolution reaction exhibits the same first-hole transfer dynamics as that in O2 evolution reaction. The rate law analysis indicates that H2O2 evolution reaction exhibits the first-order reaction kinetics, demonstrating that the rate-determining step in 2e− water oxidation reaction for H2O2 evolution is the consumption of the first-hole intermediates. Importantly, the HCO3− anion accelerates the consumption of the first-hole intermediates in 2e− water oxidation reaction by about 30 fold in rate constants or 60 fold in turnover frequency relative that in 4e− water oxidation reaction. This work sheds light on the control strategy for reaction selectivity by modulation of reaction kinetics in catalysis.