TiO2 as a Photocatalyst for Water Splitting—An Experimental and Theoretical Review

Abstract

Hydrogen produced from water using photocatalysts driven by sunlight is a sustainable way to overcome the intermittency issues of solar power and provide a green alternative to fossil fuels. TiO2 has been used as a photocatalyst since the 1970s due to its low cost, earth abundance, and stability. There has been a wide range of research activities in order to enhance the use of TiO2 as a photocatalyst using dopants, modifying the surface, or depositing noble metals. However, the issues such as wide bandgap, high electron-hole recombination time, and a large overpotential for the hydrogen evolution reaction (HER) persist as a challenge. Here, we review state-of-the-art experimental and theoretical research on TiO2 based photocatalysts and identify challenges that have to be focused on to drive the field further. We conclude with a discussion of four challenges for TiO2 photocatalysts—non-standardized presentation of results, bandgap in the ultraviolet (UV) region, lack of collaboration between experimental and theoretical work, and lack of large/small scale production facilities. We also highlight the importance of combining computational modeling with experimental work to make further advances in this exciting field.

Light‐Induced Migration of Spin Defects in TiO2 Nanosystems and their Contribution to the H2 Evolution Catalysis from Water

“…Therefore, the photoexcited e − during the delivery process to surface water molecules compete against the electron‐hole recombination, and thus, from the combination of electronic and kinetic factors, the H 2 production rates are found sluggish [25,26] . To aid the synthesis of more performant TiO 2 catalysts, without relying for improvements on the additional use of other metal/s as co‐catalyst or with the addition in the water solution of hole scavengers (e. g., MeOH, ethanol, glycerol as electron donor agents), it is pivotal to achieve deeper understanding of the nature of the photogenerated active species that are active in H + catalysis, to reveal their spatial distribution, time evolution, and to dissect the electronic/structural factors affecting their stabilities and the e − /h + recombination proclivity [27–37] . In our previous work, we reported synthesis and photocatalytic H 2 evolution rates from MeOH/water mixture of a series of anatase nano‐powders, which were thermally treated under various conditions (air, Ar, ArH 2 , and pure H 2 atmosphere) and at different temperatures (300, 500, 700, 900 °C) [38] .…”

Optically Active TiO2:Er Thin Films Deposited by Magnetron Sputtering

“…Contrary to the well-known optically active glasses [ 11 ], titanium dioxide is not so frequently encountered as a host because of much higher phonon energy (<700 cm −1 ) contributing to non-radiative relaxation [ 12 , 13 ]. Nevertheless, TiO 2 being a non-toxic wide-band-gap semiconductor with a relatively high refractive index and excellent stability in harsh environments remains one of the most extensively studied metal oxides with a vast variety of applications in photocatalysis and photoelectrochemistry [ 14 , 15 ]. However, low solar-to-chemical conversion efficiency due to the profound mismatch between the optical absorption of TiO 2 and the solar spectrum has incited a lot of efforts towards improved light harvesting.…”

Investigating and Correlating Photoelectrochemical, Photocatalytic, and Antimicrobial Properties of TiO2 Nanolayers

“…At least since the pioneering work of Fujishima and Honda in 1972 1,2 semiconducting transition metal oxides such as titanium dioxide (TiO 2 ) are intensively studied as photoanode and photocatalyst materials for photosplitting of water with ultraviolet (UV) light 3 . Recently reported record-high quantum efficiencies between 81.8 % at 437 nm and 3.2 % at 1000 nm of N-TiO 2 even opens up completely new vistas to utilize nearly the whole solar spectrum beyond the UV range for photo(electro)catalytic applications 4 .…”

“…The complexity increases even more, if different phases, dopants, artificial defects etc. are to be included 3 .…”