Enhanced TiO2 Photocatalytic 2 e– Oxygen Reduction Reaction via Interfacial Microenvironment Regulation and Mechanism Analysis

The photocatalytic oxygen reduction reaction (ORR) is a promising strategy that generates H2O2 with a lower energy input. Although great progress has been made in the development of photocatalysts, poor accessibility of O2 in photocatalysts interfacial microenvironment is the rate-limiting factor for the photocatalytic 2e– ORR and still little explored. Here, we design a simple method to regulate the hydrophobicity and O2 accessibility at a controllable crystal facet ratio of TiO2 photocatalyst by a facile stearic acid (SA) modification. The adsorption structure of SA bonding with TiO2 has been investigated in detail by Raman spectra, X-ray photoelectron spectroscopy, Fourier transform infrared spectra, and density functional theory calculations. It has been found that the stable ester bond is formed between SA molecules and the TiO2 surface, thus leading to the enhanced hydrophobicity with the increase of SA loading. The highest photocatalytic H2O2 production rate from 2e− ORR on SA-modified TiO2 can reach up to 3160 μM h–1 g–1, which is 1.69 times that of the corresponding pure TiO2 sample. From the results of electrochemical impedance spectroscopy and molecular dynamics simulation, the increase of the O2 concentration in the interfacial microenvironment benefiting from the SA modification is responsible for the enhancement of 2e– ORR activity rather than the increase of hydrophobicity.