<i>In Situ</i> Spectroscopic Identification of the Electron-Transfer Intermediates of Photoelectrochemical Proton-Coupled Electron Transfer of Water Oxidation on Au
Li-Wen Wu, Chiyan Liu, Yong Han, Yi Yu, Zhi Liu, Yifan Huang
Abstract
Experimental elucidation of the decoupling of electron and proton transfer at a molecular level is essential for thoroughly understanding the kinetics of heterogeneous (photo)electrochemical proton-coupled electron transfer water oxidation. Here we illustrate the electron-transfer intermediates of positively charged surface oxygenated species on Au (Au–OH + ) and their correlations with the rate of water oxidation by in situ microphotoelectrochemical surface-enhanced Raman spectroscopy (SERS) and ambient-pressure X-ray photoelectron spectroscopy. At the intermediate stage of water oxidation, a characteristic blue shift of the vibration of Au–OH species in laser-power-density-dependent measurements was assigned to the light-induced production of Au–OH + in water oxidation. The photothermal effect was excluded according to the vibrational frequencies of Au–OH species as the temperature was increased in a variable-temperature SERS measurement. Density functional theory calculations evidenced that the frequency blue shift is from the positively charged Au–OH species. The photocurrent-dependent frequency blue shift indicated that Au–OH + is the key electron-transfer intermediate in water oxidation by decoupled electron and proton transfer.