Titanium and Zinc Oxide Nanoparticles Are Proton-Coupled Electron Transfer Agents

Abstract

Oxidation/reduction reactions at metal oxide surfaces are important to emerging solar energy conversion processes, photocatalysis, and geochemical transformations. Here we show that the usual description of these reactions as electron transfers is incomplete. Reduced TiO(2) and ZnO nanoparticles in solution can transfer an electron and a proton to phenoxyl and nitroxyl radicals, indicating that e(-) and H(+) are coupled in this interfacial reaction. These proton-coupled electron transfer (PCET) reactions are rapid and quantitative. The identification of metal oxide surfaces as PCET reagents has implications for the understanding and development of chemical energy technologies, which will rely on e(-)/H(+) coupling.

Reduction Mechanism and Capacitive Properties of Highly Electrochemically Reduced TiO2 Nanotube Arrays

“…Schrauben et al [33] proposed a protonelectron coupled transfer mechanism for explaining interfacial photocatalytic reactions using TiO 2 or ZnO nanoparticles as the catalytic agent. The electrochemical reduction of TNAs in water is also related to the surface insertion of protons (H + ions), as suggested by several groups [13,18,[34][35][36].…”

Photocatalytic conversion of CO2 into value-added and renewable fuels

“…14B). Notably, CH 4 is the main product from CO 2 photoreduction (with a little amount of CO), demonstrating that the photocatalytic CO 2 methanation (carbon reduction, 8H + /8e − ) over NaOH-TiO 2 may follow a proton coupled electron transfer (PECT) process [108], by which the concerted transfer of excited electrons coupled with surface absorbed protons promotes the effective hydrogenation of carbonates into CH 4 .…”

Predicting and identifying reactive oxygen species and electrons for photocatalytic metal sulfide micro–nano structures

“…Moreover, it is difficult to identify photoinduced electrons using spin trapping. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO), a ESR-spin label, has been used to elucidate electron transfer and the reactivity of electrons generated during photoexcitation of ZnO and ZnO/Au hybrid nanostructures [17,18]. The model system we have developed utilizes ESR combined with spin trapping and spin labeling techniques and can provide precise information about reactive oxygen species and electron behavior.…”