Photoelectrocatalytic Conversion of Carbon Dioxide to Methanol Using Bimetallic Oxide Photocatalysts Derived from Nigerian Mineral Precursors Under Solar Irradiation

The photoelectrocatalytic reduction of carbon dioxide to methanol using solar energy represents a promising artificial photosynthesis strategy for simultaneous greenhouse gas utilisation and renewable fuel generation, and the development of efficient bimetallic oxide photocatalysts from Nigerian mineral resources would uniquely align this frontier research domain with national raw material utilisation and energy transition priorities. This study synthesises and characterises a series of copper-zinc, copper-indium, and bismuth-vanadium bimetallic oxide photocatalysts using copper ore concentrates from Zamfara State, zinc ore from Plateau State, and bismuth compounds as precursors, and evaluates their photoelectrocatalytic performance for carbon dioxide reduction to methanol and formic acid under simulated and natural solar irradiation. Photocatalyst synthesis employs co-precipitation, hydrothermal, and sol-gel routes with systematic variation of bimetallic molar ratios and calcination conditions. Comprehensive characterisation includes X-ray diffraction, UV-visible diffuse reflectance spectroscopy for bandgap determination, Mott-Schottky analysis for flat band potential and semiconductor type, Brunauer-Emmett-Teller surface area, transmission electron microscopy, X-ray photoelectron spectroscopy for surface oxidation state analysis, and photoluminescence spectroscopy for charge carrier recombination dynamics. Photoelectrocatalytic reduction experiments are conducted in a custom-designed photoelectrochemical cell with carbon dioxide-saturated bicarbonate electrolyte under AM 1.5G and natural Kano sunlight irradiation. Products are quantified by gas chromatography, ion chromatography, and nuclear magnetic resonance spectroscopy. Faradaic efficiency, quantum efficiency, turnover frequency, and apparent quantum yield metrics are calculated. Charge carrier dynamics are elucidated by time-resolved photoluminescence, transient absorption spectroscopy, and electrochemical impedance spectroscopy. An original electronic structure model correlating bimetallic oxide composition with carbon dioxide reduction selectivity is developed. Keywords: photoelectrocatalysis, carbon dioxide reduction, bimetallic oxides, solar energy, Nigerian mineral resources