Photoelectrochemical properties of p-type CuBi2O4 prepared by spray pyrolysis of carbon-free precursor aqueous solution combined with post-annealing treatment

Abstract

Energy conversion using semiconductor-based photoelectrodes for photoelectrochemical (PEC) water splitting is a promising technology that contributes to an environmentally friendly society. CuBi₂O₄ is a p-type semiconductor material that can be used in visible-light-responsive photocathodes. To date, the fabrication of CuBi₂O₄ has been examined using wet processes such as spray pyrolysis of precursor solutions containing organic solvents and organic additives. Spray pyrolysis causes problems such as CO₂ emission during the decomposition of the precursor solution. In this study, we established a carbon-free method for the fabrication of CuBi₂O₄ using a precursor solution comprising Cu(NO₃)₂ and Bi(NO₃)₃ dissolved in a dilute nitric acid aqueous solution. The aqueous precursor solution was sprayed onto F-doped tin oxide-coated glass substrates, followed by post-annealing treatment in the temperature range of 400–700 °C for 1 h in air. An annealing temperature over 500 °C provides CuBi₂O₄ as revealed by the results of X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy characterization. The PEC properties of the CuBi₂O₄ photoelectrodes were investigated to determine the optimal post-annealing conditions for maximizing the photocurrent density under AM 1.5G solar illumination. The optimized CuBi₂O₄ photoelectrodes generated a photocurrent density of −0.94 mA cm⁻² at 0.6 V vs. a reversible hydrogen electrode in a potassium phosphate aqueous solution with the H₂O₂ sacrificial reagent. This study provides rational guidelines for visible-light-absorbing p-type metal oxide-based photoelectrodes utilizing a carbon-free preparation process.