Abstract
Gallium Phosphide (GaP) has a band gap of 2.26 eV and a valance band edge that is more negative than the water oxidation level. Hence, it may be a promising material for photoelectrochemical water splitting. However, one thing GaP has in common with other III-V semiconductors is that it corrodes in photoelectrochemical reactions. Cobalt oxide (CoOx) is a chemically stable and highly active oxygen evolution reaction co-catalyst. In this study, we protected a GaP photoanode by using a 20 nm TiO2 as a protection layer and a 2 nm cobalt oxide co-catalyst layer, which were both deposited via atomic layer deposition (ALD). A GaP photoanode that was modified by CoOx exhibited much higher photocurrent, potential, and photon-to-current efficiency than a bare GaP photoanode under AM1.5G illumination. A photoanode that was coated with both TiO2 and CoOx layers was stable for over 24 h during constant reaction in 1 M NaOH (pH 13.7) solution under one sun illumination.
Highlights
The use of photoelectrochemcial (PEC) water splitting to harvest intermittent solar sources in the form of hydrogen is an attractive potential method to address the energy and environmental issues
III-V semiconductor materials have attracted for PEC water splitting due to their high-efficiency, optimal band gap, and excellent optical properties but are readily susceptible to corrosion in strongly acidic or basic aqueous solutions during PEC process [5,6,7,8,9,10,11]
A gallium phosphide (GaP) photoanode modified Cobalt oxide (CoOx) was fabricated as follows: firstly, a single-crystalline nGaP substrate was immersed in HCl solution (50% v/v) for 45 s, and washed with deionized water followed by drying with N2 gas
Summary
The use of photoelectrochemcial (PEC) water splitting to harvest intermittent solar sources in the form of hydrogen is an attractive potential method to address the energy and environmental issues. Since Honda and Fujishima in 1972 demonstrated titanium dioxide (TiO2) for PEC water splitting [1], extensive efforts have been devoted to the development of photoelectrodes with good stability and high solar-to-hydrogen efficiency. Of III-V semiconductor materials, gallium phosphide (GaP) has an appropriate band gap of 2.26 eV for harvesting a large portion of solar energy and has a valence-band edge more negative than the water oxidation potential [5,12]. GaP-based photocathodes has been extensively studied [9,10,13,14], only relatively few studies demonstrated water
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