Surface engineering of nanoporous silicon photocathodes for enhanced photoelectrochemical hydrogen production

• Published in: Catalysis science & technology 2022-09, Vol.12 (18), p.564-5648
• Main Authors: Jian, Jing-Xin, Yao, Ming-Ming, Liao, Jia-Xin, Zhou, Mu-Han, Chen, Yi-Jing, Deng, Meng-Xin, Huang, Yu-Mei, Liu, Chao-Ping, Tong, Qing-Xiao
• Format: Article
• Language: English
• Subjects: Charge transfer; Current efficiency; Dynamic stability; Electrolytes; Heterojunctions; Hydrogen evolution; Hydrogen production; Interface stability; P-n junctions; Photocathodes; Photoelectric effect; Photoelectric emission; Semiconductor materials; Silicon; Titanium dioxide; Toxicity; Water splitting
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/d2cy00830k

Silicon (Si) is a promising semiconductor material in photoelectrochemical (PEC) H 2 evolution due to its advantages of being an earth-abundant element, non-toxicity, broad absorption of the solar spectrum, high saturation current and industrial fabrication. However, shortcomings such as strong sunlight reflection, low photocurrent onset potential, slow charge-transfer dynamics at the silicon/electrolyte interface, and low stability in electrolyte limit its PEC applications. In this work, surface-engineered nanoporous Si photocathodes with controllable surface morphologies were fabricated. Compared with flat Si (f-Si), chemically-etched Si (c-Si) and electrochemically-etched Si (ec-Si), PEC-etched Si (pec-Si) exhibits advantages such as high light-harvesting efficiency, a large surface area and improved electron-transfer, resulting in dramatically enhanced PEC water splitting. Additionally, n-type TiO 2 is deposited on the Si surface to prepare a p-n heterojunction and a protective layer, which further increases the charge separation and water splitting stability. Under AM1.5G illumination, the optimized pec-Si/TiO 2 photocathode gives a high photocurrent density of −15.53 mA cm −2 at 0 V RHE , a large onset potential of 0.60 V RHE , and a high applied bias photon-to-current efficiency of 2.22% for H 2 production. The surface engineering of the nanoporous structures and p-n heterojunction brings insights into the construction of efficient photoelectrodes for solar conversion. Comparison of the nanostructured Si photocathodes fabricated by chemical etching (c-Si), electrochemical etching (ec-Si) and photoelectrochemical etching (pec-Si) and their dramatically enhanced PEC water splitting.