CuO–V₂O₅ Composite vs Single-Phase Cu₂V₂O₇: Understanding the Synergy of Mixed-Metal Oxides in Customizing Their Properties for Improved Hydrogen Evolution Reaction

This study sheds light on how the electrochemical hydrogen evolution reaction (HER) properties of Cu–V–O-based mixed-metal oxides are influenced when they are constructed into composite (CuO–V2O5) and single-phase (Cu2V2O7) systems. The X-ray diffraction (XRD) analysis revealed the coexistence of CuO and V2O5 in the composite and the formation of the single-phase structure of Cu2V2O7. The Raman spectrum of the CuO–V2O5 composite showed dominant vibrations of V2O5 over CuO, indicating its competitive properties in the composite. Optical analysis further confirmed the competitive properties of the CuO–V2O5 composite, while the Cu2V2O7 system exhibited synergistic properties. Accordingly, Cu2V2O7 demonstrated the lowest overpotential of 161 mV at a current density of 10 mA/cm2, compared to 203 mV for the CuO–V2O5 composite, which is higher than its individual components (174 mV for CuO and 181 mV for V2O5). Similarly, Tafel slope values of 128, 92, 102, and 76 mV/dec were estimated for CuO, V2O5, CuO–V2O5, and Cu2V2O7, respectively. The corresponding double-layer capacitances of 0.86, 0.59, 0.47, and 0.97 mF/cm2 were also estimated, associated with the respective electrochemical surface area of the systems. In addition, the charge transfer resistance of ∼0.4 kΩ was estimated for Cu2V2O7, which is several times lower than those of the other systems. These results indicate that in mixed-metal oxides, unless the individual components are integrated through chemical interactions, the composite system exhibits competitive properties. In contrast, the chemically interacting Cu2V2O7 system manifests synergistic properties, leading to excellent hydrogen evolution reaction (HER) efficiencies, as observed in this study.