Application of ion beam technology in modification of photoelectrode

Abstract

Semiconductor-based photoelectrolysis for water splitting to produce hydrogen and oxygen is a simple, relatively cheap and reliable way for energy utilization. Therefore, developing photoelectrode materials with high solar-to-hydrogen (STH) efficiency has become a hotspot in the field of material science. Many semiconductor-based photoelectrolysis suffer from the lack of visible light response and low charge separation efficiency resulting in low photoelectrocatalytic activity. It is particularly important to developing modified photoelectrode materials. Ion beam technology, as an important semiconductor modification technology, has been generally used to modify the electronic property of silicon. It has great potential application in modification of photoelectrode materials. Comparing with traditional modification method, ion beam technology has many advantages, such as good repeatability and controllability. Ion beam technology is an effective method for doping. Various ion species can be doped into photoelectrode materials. The ion implantation process could ensure the uniformity and purity of the introduced elements in materials. Doped ions can be highly dispersed and present at the lattice positions deeply inside the film. Basing on the works of our and other research groups, this review briefly introduces the advantages, the recent progress, and the current issues of application of ion beam technology in modifying photoelectrode materials. Ion beam technology has been used to effectively improve visible light absorption of many photoelectrode materials. TiO 2 doping through metal ion implantation has been studied since 1998. Various metal ion implantations have been found to be effective in improving material’s visible light response. Compared with metal ion implantation, only few examples of nonmetal implantation are known. Since 2005, N ion implantation was reported to be effective to improve photoelectrochemical (PEC) properties of TiO 2 , ZnO, WO 3 . Ion implantation is proven to be effective and reliable method of doping. In addition, a gradient distribution of dopants along the vertical direction of materials would be formed. The gradient distributed dopants not only enhance the visible light absorption, but also introduce a homojunction which efficiently drives photo-induced electrons and holes separation and transfers. Ion implantation introduces lots of defects into materials. The defects always are known as recombination sites of electrons and holes. Post-implantation thermal annealing process is critical for PEC performance by eliminating partial defects. However, defects introduced by ion implantation are controllable. On the one hand, by low energy ion irradiation, surface defect has formed under control in shallow zone of photoelectrode. Through defect engineering, the electronic structure of many semiconductors can be modified. An impressive promotion of electrical conductivity and more exposed of active sites can lead to remarkable enhancements in photoelectrocatalytic performance. On the other hand, by high fluence beam irradiation combination with thermal annealing, the irradiation damage can be used to form nanostructure like nanorods. Up to now, the application of ion beam technology in modifying photoelectrode materials is still at the comparatively primary stage. In order to achieve high performance photoelectrochemical water splitting using ion beam technology, more attention should be paid to the more precise control over the dopants and defects. A large number of more systematic and in-depth researches should be carried out.