Interfacial and Stability Studies of Photocathodes for Hydrogen Evolution

Citation

Jiang, Jingjing (2018) Interfacial and Stability Studies of Photocathodes for Hydrogen Evolution. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/SBJ9-D062. https://resolver.caltech.edu/CaltechTHESIS:06112018-153323554

Abstract

Photoelectrochemical (PEC) water splitting is a promising way to generate clean hydrogen fuel from water and sunlight. The ideal photocathodes for hydrogen evolution reaction (HER) should have good electrical contact and mechanical adhesion on the interface between the semiconductor and the catalyst, and be stable during operation. However, the interfacial properties and the stability have not been intensively studied. We investigated the electrical and mechanical properties on the nanoscale of the interface of commonly used Si/Pt nanoparticles (Pt-NPs) electrodes with Pt-NPs as a catalyst, and showed that the Pt-NPs have a weaker adhesion in electrolyte than in air, and less than half of the Pt-NPs carry high currents, limiting the performance of the common Si/Pt-NPs electrodes. Furthermore, we explored the interfacial engineering of using TiO₂ deposited by atomic layer deposition (ALD), and showed that annealed TiO₂ led to higher open circuit voltages than the as grown ones by the possible formation of an interfacial Si-O-Ti mixture layer. Besides, the stability and corrosion behavior of CdTe electrodes for HER in the dark was studied in 1.0 M H₂SO₄(aq) and 1.0 M KOH(aq). The conditions studied herein include the electrochemical corrosion when biased at -100 mV vs. the reversible hydrogen electrode (RHE), the chemical corrosion when left at open circuit voltage (OCV), and the electrochemical corrosion with an active HER Pt catalyst overlayer when biased at -100 mV vs. RHE. The corrosion comes mostly from chemical corrosion and is reduced at negative bias in electrochemical condition. With a Pt catalyst overlayer at -100 mV vs. RHE, the corrosion rate is further reduced, indicating the promising utilization of CdTe for HER in PEC cells.

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