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

The photocatalytic oxygen reductionreaction (ORR) is a promisingstrategy that generates H2O2 with a lower energyinput. Although great progress has been made in the development ofphotocatalysts, poor accessibility of O-2 in photocatalystsinterfacial microenvironment is the rate-limiting factor for the photocatalytic2e(-) ORR and still little explored. Here, we designa simple method to regulate the hydrophobicity and O-2 accessibilityat a controllable crystal facet ratio of TiO2 photocatalystby a facile stearic acid (SA) modification. The adsorption structureof SA bonding with TiO2 has been investigated in detailby Raman spectra, X-ray photoelectron spectroscopy, Fourier transforminfrared spectra, and density functional theory calculations. It hasbeen found that the stable ester bond is formed between SA moleculesand the TiO2 surface, thus leading to the enhanced hydrophobicitywith the increase of SA loading. The highest photocatalytic H2O2 production rate from 2e(-) ORRon SA-modified TiO2 can reach up to 3160 mu M h(-1) g(-1), which is 1.69 times that ofthe corresponding pure TiO2 sample. From the results ofelectrochemical impedance spectroscopy and molecular dynamics simulation,the increase of the O-2 concentration in the interfacialmicroenvironment benefiting from the SA modification is responsiblefor the enhancement of 2e(-) ORR activity rather thanthe increase of hydrophobicity.