How Hot Electron Generation at the Solid–Liquid Interface Is Different from the Solid–Gas Interface

Excitation of hot electrons by energy dissipation under exothermic chemical reactions on metal catalyst surfaces occurs at both solid–gas and solid–liquid interfaces. Despite extensive studies, a comparative operando study directly comparing electronic excitation by electronically nonadiabatic interactions at solid–gas and solid–liquid interfaces has not been reported. Herein, on the basis of our in situ techniques for monitoring of energy dissipation as a chemicurrent using a Pt/n-Si nanodiode sensor, we observed the generation of hot electrons in both gas and liquid phases during H₂O₂ decomposition. As a result of comparing the current signal and oxygen evolution rate in the two phases, surprisingly, the efficiency of reaction-induced excitation of hot electrons increased by ∼100 times at the solid–liquid interface compared to the solid–gas interface. The boost of hot electron excitation in the liquid phase is due to the presence of an ionic layer lowering the potential barrier at the junction for transferring hot electrons.