Hervin Errol Mendoza1,Zongkai Wu1,Samutr Assavachin1,Chengcan Xiao1,Frank Osterloh1
University of California, Davis1
Hervin Errol Mendoza1,Zongkai Wu1,Samutr Assavachin1,Chengcan Xiao1,Frank Osterloh1
University of California, Davis1
Semiconductor-based solar water splitting for renewable fuel generation is one of the practical means of addressing the increasing global energy demand. Cu<sub>2</sub>O (p-type, E<sub>g</sub> = 2.0 eV) is earth-abundant and inexpensive while BiVO<sub>4</sub> (n-type, E<sub>g</sub> = 2.4 eV) is preparable using scalable methods, making these two materials suitable choices for cost-efficient and sustainable energy production. A Cu<sub>2</sub>O/BiVO<sub>4</sub> structure with a theoretical solar-to-hydrogen efficiency of 9.2% can potentially exhibit unassisted water splitting, but very few studies have been carried out to investigate this system (Wu, Z. et al., Chem. Comm., 2018, 54(65), 9023-9026). In this work, bilayer photoelectrodes were constructed from Cu<sub>2</sub>O and Mo-doped bismuth vanadate (Mo:BiVO<sub>4</sub>) and characterized. Cu<sub>2</sub>O was electrodeposited onto a F-doped tin oxide (FTO) substrate and Mo:BiVO<sub>4</sub> nanoparticles were prepared by solution phase synthesis. The bilayer was then obtained through electrophoretic deposition of Mo:BiVO<sub>4</sub> on Cu<sub>2</sub>O followed by argon annealing at 550<sup>o</sup>C for 8 hrs. X-ray diffraction data indicated the formation of new phases in the film after annealing. Photoelectrochemical experiments in 0.1 M Na<sub>2</sub>SO<sub>4</sub> solution at pH 7 showed anodic photocurrent with onset potential of ~0.6 V vs. reversible hydrogen electrode (RHE). Surface photovoltage spectroscopy suggests formation of a pn junction between Cu<sub>2</sub>O and Mo:BiVO<sub>4</sub>, likely causing the device to work only under applied bias conditions. Use of oxygen evolution cocatalysts and charge selective contacts had been explored in an attempt to mitigate the issue.