Photoelectrochemical cells (PECs) can directly utilize solar energy to drive chemical reactions to produce fuels and chemicals. Oxide-based photoelectrodes in general exhibit enhanced stability against photocorrosion, which is a critical advantage for building a sustainable PEC. However, most oxide-based semiconductors are n-type, and p-type oxides that can be used as photocathodes are limited. In this study, we report the synthesis, characterization, and application of p-type BiVO with a monoclinic scheelite () structure. -BiVO is inherently n-type, and it has been investigated only as a photoanode to date. In this study, we prepared p-type -BiVO (bandgap of 2.4 eV) via atomic doping of Ca at the Bi site under an O-rich environment and examined its performance as a photocathode. We then demonstrated that the Ca-doped -BiVO photocathode can be used for solar O reduction to HO when coupled with appropriate catalysts. Our computational investigation using hybrid density functional theory revealed that holes are stable as polarons in -BiVO and have a low self-trapping energy, that may lead to free carriers in the valence band at finite temperature. Our calculations also show that Ca is an effective shallow acceptor dopant with low formation energy and thermal ionization energy leading to p-type conductivity. Our joint experimental and computational results provide critical insights into the design of p-type -BiVO, enabling its use as a polaronic oxide photocathode.
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p-Type BiVO for Solar O Reduction to HO.
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Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
Photoelectrochemical cells (PECs) can directly utilize solar energy to drive chemical reactions to produce fuels and chemicals. Oxide-based photoelectrodes in general exhibit enhanced stability against photocorrosion, which is a critical advantage for building a sustainable PEC. However, most oxide-based semiconductors are n-type, and p-type oxides that can be used as photocathodes are limited.
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Article Synopsis
- Water oxidation is a slow, endothermic process, making the development of efficient photoanodes important for solar water splitting.
- The study found that BiVO/CoAlO film photoanodes, combining n-type BiVO and p-type CoAlO, resulted in a photocurrent of 3.47 mA/cm, significantly outperforming the BiVO-only photoanode (1.70 mA/cm).
- The enhanced performance of the BiVO/CoAlO photoanode is attributed to the beneficial p-n heterojunctions, photothermal effects that raise temperature to about 53°C under light irradiation, and improved cocatalytic activity.
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