In an air-saturated neutral electrolyte solution, a Cu2O (copper(I) oxide) photocathode continuously produces a significant size of photocurrent (0.7 mA/cm2 at –0.4 V vs SCE). Hydrogen generation at a Cu2O photocathode is presently considered to be a minor contributor to this relatively large photocurrent. The source of the relatively high photocurrent has been speculated upon, but has not yet been identified. Considering the importance of H2O2 as a commodity chemical and a potential alternative to the current expensive anthraquinone + Pd catalyst method for H2O2 production, we have investigated H2O2 generation at a Cu2O photocathode (O2 + 2 H2O + 2 e– → H2O2 + 2 OH– E = 0.09 V vs SCE at pH 7). Copper(I) oxide thin films were prepared via electrodeposition of Cu2O on indium tin oxide coated glass. The electrolyte solution (0.5 M Na2SO4) was bubbled with O2(g) for 10 min prior to the experiment, and the surface of the electrolyte solution was covered with O2(g) during the experiment. The Cu2O was illuminated with a 100-W tungsten lamp, and a portion of the electrolyte solution (2 mL) was collected and tested with POPHA (p-hydroxylphenylacetic acid) reagent for fluorescence (λex= 315 nm, λem= 406 nm) in order to measure H2O2 concentration for 20 min after starting the illumination. The potential of the photocathode was controlled to be at 0, –0.1, –0.2, or –0.3 V vs SCE. The concentration of H2O2 increased over time for all of the applied potentials. The generation of H2O2 peaked at –0.2 V, and the largest H2O2 concentration was 3.6 × 10–7 M. This concentration indicates 6.9 × 10–3 C of charge was spent for H2O2 formation. The total charge passed during the experiment was 1.2 × 10–2 C, therefore, the efficiency of H2O2 production was calculated to be approximately 60%.

Hydrogen peroxide generation at Cu2O photocathode

2019 Spring National Meeting

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