Strategies for reducing the overpotential of one-dimensional Si nanostructured photoelectrodes for solar hydrogen production

Abstract

Using solar energy to split water to produce hydrogen, the most promising green energy source, is an advanced way to solve the current energy crisis and environmental pollution problems. The key to this technology lies in the development of high-performance semiconductor photoelectrodes. Si has been recognized as a promissing candidate for solar water splitting photoelectrodes due to its excellent light absorption properties (band gap of 1.1 eV), high carrier mobility, abundance on earth, and established manufacturing technology. To improve the performance of Si-based photoelectrodes, one-dimensional (1D) Si nanostructures have been constructed and investigated. 1D Si nanostructured photoelectrodes have many advantages over planar Si photoelectrodes, including a large specific surface area that provides more reaction sites, antireflection effect that greatly enhances the absorption of sunlight, and improved carrier utilization by decoupling the light absorption and carrier collection paths. However, the poor catalytic activity of Si itself for the water splitting reactions (oxygen evolution reaction and hydrogen evolution reaction) makes the photoelectrocatalytic (PEC) water splitting on Si-based photoelectrodes require a large overpotential. In addition, the narrow band gap of Si leads to a low photovoltage, and the valence band energy level of Si is insufficient to oxidize water, which also leads to an increased overpotential for the PEC water splitting by the Si-based photoelectrodes. In order to reduce the overpotential of 1D Si nanostructured photoelectrodes for PEC water splitting, several strategies have been proposed, such as loading co-catalysts and constructing hetero- and homo-junctions. After introducing PEC water splitting process on Si, and the preparation methods and advantages of 1D Si nanostructures, this review paper provides an overview of the strategies and recent advances in reducing the overpotential of 1D Si nanostructured photoelectrodes for PEC water splitting.