Investigation of silicon carbonitride/silicon for photoelectrochemical CO₂ reduction

Silicon carbonitride (SiCN) thin films were deposited on p-type silicon (Si) substrates by reactive radio-frequency magnetron sputtering using a silicon carbide (SiC) target under argon/nitrogen (Ar/N₂) plasma at room temperature. Characterization by Fourier-transform infrared, electron probe micro analyzer, and X-ray photoelectron spectroscopy indicates the formation of silicon carbonitride. Diffuse reflectance data processed by way of Tauc plot analysis resolved an optical bandgap of 2.05 eV, in agreement with photoluminescence emission data. Photoelectrochemical (PEC) carbon dioxide (CO₂) reduction tests were conducted under natural sunlight irradiation at a bias of −1.2 V against silver/silver chloride (Ag/AgCl) in 0.1 M sulfuric acid (H₂SO₄). Quantitative gas chromatography-flame ionization detector analysis showed liquid-phase selectivity toward methanol, yielding a Faradaic efficiency of 40.9%, which corresponds to a cumulative molar yield of 19.07 µmol (0.191 mmol/L) after 1 h of continuous operation. These results quantify the PEC performance of amorphous silicon carbonitride (a-SiCN)/silicon photocathodes for solar-driven carbon dioxide conversion.