Abstract
It is highly desired to effectively trap photogenerated holes for efficient photoelectrochemical (PEC) water oxidation to evolve O2 on oxide semiconductors. Herein, it is found for the first time mainly based on the time-resolved- and atmosphere-controlled- surface photovoltage responses that the modified chloride would effectively trap photogenerated holes so as to prolong the charge lifetime and hence promote charge separation of single-crystal rutile TiO2 nanorods. Its strong capacity to trap holes, comparable to the widely-used methanol and Co(II) phosphate, is well responsible for the exceptional photoactivities for PEC water oxidation to evolve O2 on rutile nanorods with a proper amount of chloride modified, about 2.5-time high as that on the resulting anatase nanoparticles, even 10-time if the surface area is considered. Moreover, it is suggested that the hole trapping role of chemically-adsorbed chloride is related to its lonely-pair electrons, and to the subsequently-produced intermediate Cl atoms with proper electronegativity for evolving O2. Interestingly, this finding is also applicable to the chloride-modified anatase TiO2. This work will provide a feasible strategy to design high-activity nanostructured semiconductor photoanodes for PEC water oxidation, even for overall water splitting.
Highlights
To realize the potential benefits of solar energy as a renewable energy source, it is desirable to develop a method to efficiently convert and store solar energy[1,2,3]
In our previous works[16,22], it is clearly demonstrated that the formed surface negative fields after modification with phosphoric acids could prolong the lifetime of photogenerated charges of nano-sized TiO2 and BiVO4 by trapping photogenerated holes, leading to the enhanced photoactivities for PEC water oxidation
It is noticed that the content percentage of rutile phase mainly depends on the concentration of HCl used, and it gradually become large with increasing the HCl amount
Summary
To realize the potential benefits of solar energy as a renewable energy source, it is desirable to develop a method to efficiently convert and store solar energy[1,2,3]. As for this, cobalt-based co-catalysts have been well investigated for efficient PEC water oxidation on TiO218–20 In those works, it has been clearly demonstrated that the modified Co species could trap photogenerated holes effectively to produce high-valence Co ions, further inducing oxidation reactions with water molecules and subsequently returning to the original-valence ones. Based on the above analyses, we try to deeply reveal the effects of modified chloride on the photogenerated hole trapping, charge carrier lifetime, charge separation and photoactivities for PEC water oxidation to evolve O2 on single-crystal rutile TiO2 as a model system, mainly by means of time-resolved- and atmosphere-controlledsurface photovoltage responses, especially in N2 atmosphere. This work will provide a feasible strategy to design high-activity nanostructured semiconductor photoanodes for PEC water oxidation to produce O2, even for photocatalytic overall water splitting
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