Kenaf-derived carbon quantum dots-modified BiVO4 thin film photoanodes for enhanced photoelectrochemical water splitting and hydrogen generation.

Bismuth vanadate (BiVO4) is a promising visible-light photocatalyst for PEC hydrogen production owing to its favourable band-edge positions, but its practical efficiency is hindered by rapid electron-hole recombination and consequently poor solar-energy conversion. Herein, a green approach using different loading amounts of kenaf-based carbon quantum dots (CQDs) as electron transfer mediators is applied to enhance the optical and electrical properties of the BiVO4 photoanode. CQDs boosted the light absorption of the modified BiVO4 photoanode across 300-800 nm and narrowed the band gap energy from 2.35 eV to 2.27 eV. In addition, the as-developed CQDs/BiVO4 exhibited higher charge separation efficiency, with a 36.0% reduction in charge recombination at 469 nm. At 1.05 V vs. RHE, the optimum CQDs/BiVO4 (CB-14) demonstrated a photocurrent density of 0.254 mA cm-2, approximately two-fold higher compared to the unmodified BiVO4. It also exhibited a 166.7% increment in photoconversion efficiency upon modification with kenaf-based CQDs (CB-14). An average hydrogen evolution of 10.83 µmol cm-2 h-1 was recorded by CB-14, which is 1.67 times higher compared to the unmodified BiVO4.