“Roll-on” nano-CIGSe film electrodes in photo-hydrogenation

• “Roll-on” nano-CIGSe films on ITO substrates show photo-transients consistent with photo-hydrogenation processes.
• Photo-generator-collector experiments with a Pt microelectrode provide information about product formation during photo-transient measurements.
• Fumaric acid is an ideal irreversible quencher giving succinic acid without solution phase recombination pathways.

Commercial nano-CIGSe powder (nominal CuIn0.7Ga0.3Se2, average particle size < 100 nm) is applied to tin-doped indium oxide (ITO) electrodes in a simple “roll-on” process from n-hexanol to give thin photo-electrochemically active films. Films “as deposited” and “annealed” in selenium atmosphere at 350 °C are compared with the latter performing substantially better. Perhaps surprisingly, photo-transient voltammetry suggests only insignificant effects when changing aqueous electrolyte from Eu(NO3)3 to KNO3 or when changing electrolyte concentration, most likely due to a dominating electron-quenching process caused by dissolved dioxygen. However, when under inert argon atmosphere, generator-collector photo-transient voltammetry with a 50 μm Pt collector microelectrode placed close to the CIGSe film surface proves photo-induced H2 formation in 0.1 M KNO3 or in 0.1 M HNO3 (and it confirms electron-quenching by O2 in the presence of air). In aqueous 0.1 M HNO3 effective electron-quenching (photo-hydrogenation) with fumaric acid is observed with current yields of ca. 60% for fumarate to succinate conversion. Detrimental loss of photoelectrochemical activity (probably via photo-corrosion) with time occurs.

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