Abstract
Although the α-SnWO4 material has recently been considered as a new good candidate for visible-light-driven photo(electro)chemical water splitting, the performance is still low and requires further improvement. Here, we present a deep fundamental work on the influence of the various possible facets exposed on this material for oxygen and hydrogen evolution reactions using hybrid density functional theory. The energetic, electronic, water redox, and charge carrier transport features of the four possible (100), (010), (001), and (110) facets (low-Miller index surfaces) are investigated, and significant anisotropic nature is revealed. The relevant properties of each facet to the water oxidation/reduction reactions are correlated with the surface W coordination number. Taking into account the stability and combining optoelectronic and water redox features together of each surface, our work demonstrates that the (110) facet is photocatalytically the best candidate for the OER, while the (100) facet is the best candidate for the HER. Their transport characteristics are found to be much better than those obtained for the three major (121), (210), and (111) facets of synthesized α-SnWO4 samples. Substitutional Ge at the Sn site and Mo at the W site on the two (110) and (100) facets are expected to increase the rates of the water oxidation/reduction reactions. An analysis of the reaction mechanism for the OER in (110)-oriented α-SnWO4 reveals a promising performance of this facet for electrocatalytic water oxidation. These outcomes will greatly motivate experimentalists for carefully designing (110)- and (100)-oriented α-SnWO4 samples to enhance the photo(electro)catalytic OER and photocatalytic HER performances.
Highlights
Solar water splitting for hydrogen production by photo(electro)catalysis using a semiconductor-based heterogeneous catalyst is one of the promising technologies for a clean energy future and a sustainable green environment at low cost.[1−6] Considerable efforts have been made on developing an operating and ideal photocatalyst by monitoring its fundamental characteristics to acquire both O2 and H2 evolution reactions, HER and oxygen evolution reaction (OER), and to achieve high conversion efficiency
Taking into account the stability and combining optoelectronic and water redox features together of each surface, our work demonstrates that the (110) facet is photocatalytically the best candidate for the OER, while the (100) facet is the best candidate for the HER
The core electrons were sketched by projector-augmented wave (PAW) potentials,[59] with 5s25p2, 5d46s2, 2s22p4, 4s24p2, and 4d45s2 valence of 2D sheets of distorted corner-sharing WO6 octahedra and separated by layers of 4-fold coordinated edge-sharing Sn2+
Summary
Solar water splitting for hydrogen production by photo(electro)catalysis using a semiconductor-based heterogeneous catalyst is one of the promising technologies for a clean energy future and a sustainable green environment at low cost.[1−6] Considerable efforts have been made on developing an operating and ideal photocatalyst by monitoring its fundamental characteristics to acquire both O2 and H2 evolution reactions, HER and OER, and to achieve high conversion efficiency. Appropriate VBM and CBM energy positions should lie below O2/H2O and above H+/H2 potentials, respectively, to drive the holes and electrons for oxidizing water and reducing protons.[7,8] The well-delocalized involved orbitals in the VBM/CBM electronic states are vital to secure good hole/electron mobility throughout the material crystal lattice to the surface.[9−13] To enhance the photocatalytic properties, various strategies have been outlined either by introducing co-catalysts on the electrode surfaces to improve the kinetics of holes and electron transfers to the electrolyte or by fabricating heterojunctions.[14−17] Among them, exposed facet engineering has been reviewed as a promising way to tune the material characteristics and improve the photocatalytic activity results.[18−21]. Various synthesis protocols of α-SnWO4 samples led to various morphologies and diverse photocatalytic results.[28−34] To help for easier charge separation and higher efficiency, careful synthesis approaches for α-SnWO4 with particular exposed facets are indispensable
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