Facile room-temperature growth of nanostructured CuBi2O4 for selective electrochemical reforming and photoelectrochemical hydrogen evolution reactions

Abstract

Facile, room-temperature, and surfactant-free seed-mediated chemical bath deposition was developed to directly grow CuBi₂O₄ nanostructures on an electrode substrate for applications in electrochemical reforming of glucose and photoelectrochemical (PEC) hydrogen generation. The metal precursor concentration and Cu²⁺/Bi³⁺ molar ratio were found to be decisive factors in determining the structure of CuBi₂O₄, and single crystal CuBi₂O₄ submicron-square columns (microCuBi₂O₄), nano-square columns (nanoCuBi₂O₄), and c-axis oriented nano-square columns (c-nanoCuBi₂O₄) were selected for detailed electrochemical and PEC characterization. The results of Tauc plots and ultraviolet photoelectron spectroscopy (UPS) resolved the band structure of these CuBi₂O₄ compounds. Mott–Schottky and UPS analyses showed that these CuBi₂O₄ compounds had flat-band potentials of >1.10 V vs. RHE, which makes them promising photocathodes for PEC hydrogen generation. The synthesized CuBi₂O₄ compounds exhibited different levels of electrocatalytic activity towards electroreforming of glucose, in the order of nanoCuBi₂O₄ > c-nanoCuBi₂O₄ > microCuBi₂O₄, which is attributed to the structure-dependent kinetics of the chemical reaction between glucose and electrochemically activated Cu species in CuBi₂O₄ at elevated anodic potentials. Additionally, all synthesized CuBi₂O₄ samples showed high selectivity (faradaic efficiency > 93%) for formate generation from electro-oxidative conversion of glucose. This study opens up a new avenue for the synthesis of nanostructured CuBi₂O₄ with promising bi-functionality towards PEC biomass reforming.