An integrated cobalt disulfide (CoS 2 ) co-catalyst passivation layer on silicon microwires for photoelectrochemical hydrogen evolution

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2015-01, Vol.3 (46), p.23466-23476
• Main Authors: Chen, Chih-Jung, Chen, Po-Tzu, Basu, Mrinmoyee, Yang, Kai-Chih, Lu, Ying-Rui, Dong, Chung-Li, Ma, Chong-Geng, Shen, Chin-Chang, Hu, Shu-Fen, Liu, Ru-Shi
• Format: Article
• Language: English
• Subjects: Cobalt; Electrodes; Hydrogen evolution; Passivation; Photocathodes; Photocurrent; Photoelectric effect; Silicon
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c5ta06202k

An integrated cobalt disulfide (CoS2) co-catalyst passivation layer on Si microwires (MWs) was used as a photocathode for solar hydrogen evolution. Si MWs were prepared by photolithography and dry etching techniques. The CoS2-Si photocathodes were subsequently prepared by chemical deposition and thermal sulfidation of the Co(OH)2 outer shell. The optimized onset potential and photocurrent of the CoS2-Si electrode were 0.248 V and -3.22 mA cm-2 (at 0 V), respectively. The best photocatalytic activity of the CoS2-Si electrode resulted from lower charge transfer resistances among the photoabsorber, co-catalyst, and redox couples in the electrolyte. X-ray absorption near edge structure was conducted to investigate the unoccupied electronic states of the CoS2 layer. We propose that more vacancies in the S-3p unoccupied states of the CoS2-Si electrode were present with a lower negative charge of S22- to form weaker S-H bond strength, promoting water splitting efficiency. Moreover, the CoS2 co-catalyst that completely covered underlying Si MWs served as a passivation layer to prevent oxidation and reduce degradation during photoelectrochemical measurements. Therefore, the optimal CoS2-Si electrode maintained the photocurrent at about -3 mA cm-2 (at 0 V) for 9 h, and its hydrogen generation rate was approximately 0.833 mu mol min-1.