Cl- ions accelerating interface charge transfer in a Si/In2S3 faradaic junction photocathode for solar seawater splitting

This study is led by Prof. Wenjun Luo (College of Engineering and Applied Sciences, Nanjing University). In previous studies, the effects of Cl^- ions in seawater on the performance of a photoanode have been widely reported. In contrast, there are few reports on the effects of Cl^- ions on photocathodes. Therefore, it is very desirable to investigate the effects of Cl^- on the photocathode to further improve the efficiency for solar seawater splitting.

In this work, p-Si was utilized as a photocathode substrate, and then coated with n-In₂S₃ films on its surface to form a Si/In₂S₃ heterojunction photocathode. The Cl^- ions in the electrolyte can increase the photocurrent of the Si/In₂S₃ heterojunction photocathode by 50% at the potential of -0.6 V_RHE. The results of in-situ XPS, time-of-flight secondary-ion mass spectrometry (TOF-SIMS) and electrochemical measurements suggest that coupled electron and ion transfer process (faradaic junction) happens at the interface of the Si/In₂S₃ heterojunction photocathode, which is different from the conventional electron transfer process at the heterojunction interface.

The results also suggest that there is an In₂⁺³S_3-x(OH)_2x layer on the surface of In₂S₃ in the phosphate buffer solution (PBS) electrolyte, and the surface layer of the In₂S₃ plays a role as an interface charge transfer mediator in the Si/In₂S₃ photocathode through the coupled electron and ion transfer process. After adding Cl^- ions into the PBS electrolyte, the surface layer of In₂S₃ becomes to In₂⁺³S_3-x(Cl)_2x, which indicates faster electron transfer rate into H⁺ in electrolyte than H_2yIn₂^+(3-y)S_3-x(OH)_2x and leads to a higher photocurrent of the Si/In₂S₃ photocathode in the PBS electrolyte with Cl^- ions.

These results deepen the understanding of charge transfer on the surface of In₂S₃ and the interface of Si/In₂S₃, and would offer a new concept of regulating interface charge transfer mediator to enhance the performance of photoelectrocatalytic seawater splitting for hydrogen production.

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See the article:

Cl^- ions accelerating interface charge transfer in a Si/In₂S₃ faradaic junction photocathode for solar seawater splitting

https://doi.org/10.1007/s11426-024-2119-2