Abstract
The origin of instability of p-Cu2O films deposited on a platinized Si substrate when used as photocathode in photoelectrochemical water splitting, was studied in the absence or presence of a protective layer of RuO2. When applied at +0.3V vs. RHE and at pH 7, p-Cu2O films were found to show a slightly more stable performance as compared to photoelectrochemical measurements reported in the literature at 0V vs. RHE and under acidic conditions. In addition, the stability and the photocurrent induced by the Cu2O films were significantly improved when H2O2 was added to the electrolyte, which is explained by efficient scavenging of electrons, yielding oxygen and water as confirmed by gas chromatography (GC). Also, other electron acceptors improved the photocatalytic performance of the p-Cu2O films, demonstrating that the transfer of photo-excited electrons to protons adsorbed on the surface is the rate determining step in p-Cu2O based photo-electrochemical water splitting. We confirmed that deposition of RuO2 improves the stability of the films, but to the expense of a decrease in photocurrent density. The results provided in this study rationalize the attachment of an effective H2 evolution catalyst as a means to significantly improve the stability of p-Cu2O electrodes.
Highlights
One of the techniques that is emerging as a promising method for storage of renewable energy, is photocatalytic or photoelectrochemical splitting of water, yielding hydrogen gas
The first three techniques have the advantage that the photocurrent was simultaneously enhanced with the stability, but their disadvantage is that the photocurrent still decreases significantly within the first 20 minutes; only the protection with an additional RuO2 layer seems to be capable of improving the photoelectrochemical stability of Cu2O as photocathode, showing 94% of its initial activity after 8 h of illumination [15]
We studied the effect of different hole and electron scavengers on both the photocatalytic activity and the photoelectrochemical stability of Cu2O films in the absence or presence of a RuO2 layer, in order to evaluate the limiting factors that result in the poor performance of Cu2O
Summary
One of the techniques that is emerging as a promising method for storage of renewable energy, is photocatalytic or photoelectrochemical splitting of water, yielding hydrogen (and oxygen) gas. From the Pourbaix diagram it can be observed that shifting the applied potential from 0 V vs RHE to 0.3 V vs RHE and by using an electrolyte with neutral pH, Cu2O is already more stable, and the use of a protective coating is not principally necessary [20] We used these conditions (pH 7 and 0.3 V vs RHE) in the present study for the evaluation of the photocatalytic activity of different Cu2O films deposited on a platinized Si substrate, serving as a model substrate for the metallic divider proposed by Zoontjes et al [7]. It is known that electron acceptors, such as H2O2, improve the stability of Cu2O, we provide more detail in the chemistry and Faradaic efficiency of these Cu2O films by combining PEC measurements with ultrasensitive real-time Gas Chromatography measurements (allowing H2 and O2 detection in the ppb range)
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