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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.

Temperature variation at the nanoscale is pivotal for the thermodynamics and kinetics of small entities. Surface-enhanced Raman spectroscopy (SERS) is a promising technique for monitoring temperature variations at the nanoscale. A key but ambiguous topic is methods to design a sensitive SERS thermometer. Here, we elucidate that the type of chemical bond of molecular probes and the surface chemical bonding effect are crucial for maximizing the sensitivity of the SERS thermometer, as illustrated by the variable-temperature SERS measurements and quantum chemistry calculations for the frequency–temperature functions of a series of molecules. The sensitivity of the frequency–temperature function follows the sequence of triple bond > double bond > single bond, which is available for both aliphatic and aromatic molecules. The surface chemical bonding effect between the SERS substrate and molecular probe substantially increases the sensitivity of the frequency–temperature function. These results provide universally available guidelines for the rational design of a sensitive SERS thermometer by examining the functional groups of molecular probes.

To understand the roles of Au(III) (hydro-)oxides in promoting plasmon-mediated photoelectrochemical (PMPEC) water-oxidation, we employed in-situ microphotoelectrochemical surface-enhanced Raman spectroscopy and ambient-pressure X-ray photoelectron spectroscopy to elucidate the correlations between the amount of surface Au(III) (hydro-)oxides and the photocurrent of PMPEC water-oxidation on Au. By applying preoxidation potentials, we made surface Au(III) (hydro-)oxides on a plasmonic Au photoanode. According to the charge of reductively stripping surface oxygenated species before and after PMPEC water-oxidation, we found that a negative shift of an onset potential, increase in photocurrent, and much less growth of surface (hydro-)oxides was correlated as a result of the increase in the coverage of Au (III) (hydro-)oxides. These results suggest that the surface Au(III) (hydro-)oxides kinetically promoted water-oxidation through restricting the growth of surface (hydro-)oxides.