Activating Titania for Efficient Electrocatalysis by Vacancy Engineering

Abstract

Pursuing efficient and low-cost electrocatalysts is crucial for the performance of water-alkali electrolyzers toward water splitting. Earth-abundant transition-metal oxides, in spite of their alluring performances in the oxygen evolution reaction, are thought to be inactive in the hydrogen evolution reaction in alkaline media. Here, we demonstrate that pure TiO 2 single crystals, a typical transition-metal oxide, can be activated toward electrocatalytic hydrogen evolution reaction in alkaline media through engineering interfacial oxygen vacancies. Experimental and theoretical results indicate that subsurface oxygen vacancies and low-coordinated Ti ions (Ti 3+) can enhance the electrical conductivity and promote electron transfer and hydrogen desorption, which activate reduced TiO 2 single crystals in the hydrogen evolution reaction in alkaline media. This study offers a rational route for developing reduced transitionmetal oxides for low-cost and highly active hydrogen evolution reaction catalysts, to realize overall water splitting in alkaline media.

Defect Engineering of Photocatalysts for Solar Energy Conversion

“…Meanwhile, EELS can be used to analyze the distribution of the defects in the photocatalysts. As shown from Ti–L edge spectra, the enhanced concentration of Ti 3+ ions indicated the increasing content of OVs in reduced TiO 2 crystals . In particular, the valuable information could be obtained by EPR spectroscopy.…”

“…Reproduced with permission . Copyright 2019, Elsevier Ltd. e) STM images of hydroxylated TiO 2 surface with OVs and ad‐H 2 O. Reproduced with permission . Copyright 2018, American Chemical Society.…”

“…[106] For instance, the hexagonal lattice of bright features was indexed to the outer chalcogen atoms by CO-tip noncontact-AFM, confirming the identification of the lattice sites of MoSe 2 . [106] Moreover, three bright protrusions on hydroxylated TiO 2 surface were observed by STM, [109] indicating the visualization of OVs as point defects, adsorbed H 2 O (ad-H 2 O) molecules, and OH groups and thus proving a promising way for the visualization investigation of the defects (Figure 11e). Furthermore, energy dispersive X-ray spectroscopy and inductively coupled plasma atomic emission spectroscopy can also be used for the characterization of the defects.…”

“…As shown from Ti-L edge spectra, the enhanced concentration of Ti 3þ ions indicated the increasing content of OVs in reduced TiO 2 crystals. [109] In particular, the valuable information could be obtained by EPR spectroscopy. Moreover, the enhanced EPR signals of Bi 2 WO 6 (BWO) with OVs after the reduction treatment at different temperatures confirmed the existence and the increasing content of OVs in BWO layers (Figure 12g).…”

Direct Observation of Oxygen Vacancy Self‐Healing on TiO2 Photocatalysts for Solar Water Splitting

“…[18,19] Furthermore,o wing to the low-coordination numbers,t hese Vos could significantly induce the outward driving forces for hole trapping,t hus promoting the charge separation. [21] Although the computational simulations represented by density functional theory (DFT) calculations are effective in investigating the chemical states of Vosu nder ideal conditions, [22,23] the direct study of dynamic changes of Vosatthe atomic level during water splitting process still remains ag reat challenge until now. [21] Although the computational simulations represented by density functional theory (DFT) calculations are effective in investigating the chemical states of Vosu nder ideal conditions, [22,23] the direct study of dynamic changes of Vosatthe atomic level during water splitting process still remains ag reat challenge until now.…”