Surface/Interface Engineering of Si-Based Photocathodes for Efficient Hydrogen Evolution

Abstract

Solar-driven photoelectrochemical (PEC) water splitting into hydrogen fuel is a promising avenue for renewable energy conversion to overcome energy crises and environmental concerns. Earth-abundant Si semiconductors with excellent light-harvesting capabilities are suitable photocathode candidates for the PEC hydrogen evolution reaction (HER), but suffer from intrinsic instability and sluggish kinetics. Extensive studies have demonstrated that surface/interface engineering can serve as an effective strategy for fabricating Si-based photocathodes with sufficient surface catalytic activity and facile interfacial carrier transport. In this Review, we first briefly introduce the current status of PEC HER using Si-based photocathodes and summarize their fabrication techniques. Subsequently, a systematic overview of recent achievements in surface/interface engineering of Si-based photocathodes is presented to illustrate their distinct roles in boosting the PEC-HER performance. Finally, the perspective views regarding the further development of practical Si-based photocathodes are discussed. This Review aims to promote an in-depth understanding and technical evaluation of surface/interface engineering strategies for efficient Si-based PEC HER.

A p-n-p Configuration Based on the Cuprous Oxide/Silicon Tandem Photocathode for Accelerating Solar-Driven Hydrogen Evolution

“…To enhance the PEC-HER performance over the integrated tandem PEC photocathode, the following points are considered crucial: − (i) broad light absorption range, (ii) effective charge separation in the bulk and interface and transport to the photoelectrode surface, and (iii) efficient utilization of photogenerated carriers for the catalytic center with minimum overpotential. Therefore, the second and third aspects are pivotal to designing strategies for the photocathode and reaching our final objective.…”

Robust SrTiO3 Passivation of Silicon Photocathode by Reduced Graphene Oxide for Solar Water Splitting

“…The basic requirements of a suitable photoelectrode lie in the photoactivity of a photoabsorber producing electron/hole pairs upon illumination, the solar-to-chemical conversion efficiency, and the long-term operational stability . Various material systems have been explored as photocathodes for the hydrogen evolution reaction (HER), such as p-InP, CdTe, Cu 2 O, , p-Si, − to name a few. Silicon has several advantages in the HER application, including its narrow bandgap of 1.12 eV which enables the absorption of solar spectrum up to ∼1107 nm, its favorable conduction band edge alignment with respect to proton reduction potential (E­(H 2 O/H 2 )) that expedites hydrogen production, and the high theoretical current densities of ∼44 mA cm –2 with a delivered photovoltage of 800 mV which is beneficial for decreasing the overpotential of the solar water splitting reaction .…”

“…Various material systems have been explored as photocathodes for the hydrogen evolution reaction (HER), such as p-InP, CdTe, Cu 2 O, , p-Si, − to name a few. Silicon has several advantages in the HER application, including its narrow bandgap of 1.12 eV which enables the absorption of solar spectrum up to ∼1107 nm, its favorable conduction band edge alignment with respect to proton reduction potential (E­(H 2 O/H 2 )) that expedites hydrogen production, and the high theoretical current densities of ∼44 mA cm –2 with a delivered photovoltage of 800 mV which is beneficial for decreasing the overpotential of the solar water splitting reaction . However, silicon is prone to oxidation and the intrinsic thermodynamic instability easily leads to the corrosion of silicon when in contact with an electrolyte of high ionic strength .…”

“…Numerous materials have been developed as a passivation layer to protect p-Si photocathodes from oxidation and (photo)­corrosion under the PEC operational conditions. ,,− Among them, transition metal oxides (e.g., TiO 2 , Al 2 O 3 , Ta 2 O 5 , etc.) have attracted great interest due to their optical transparency and robust chemical stability .…”

“…Numerous materials have been developed as a passivation layer to protect p-Si photocathodes from oxidation and (photo)­corrosion under the PEC operational conditions. ,,− Among them, transition metal oxides (e.g., TiO 2 , Al 2 O 3 , Ta 2 O 5 , etc.) have attracted great interest due to their optical transparency and robust chemical stability . When integrated with Si, these oxides with the visible light transparency allow most of the incident solar light to be harvested by the underlying Si photoabsorber, and at the same time, their chemical inertness enables the passivated photoelectrode to function well for an extended lifetime.…”