Photoelectrochemical performance of titanium dioxide homojunction decorated by biomass-based carbon quantum dots for water splitting

The bandgap of biomass-derived CQDs can be tuned through the decoration of nitrogen-contained compounds. • Red-emitting CQDs exhibited the narrowest bandgap and the strongest visible light absorption capacity. • The composite photoelectrode assembled by Red-emitting CQDs and TiO 2 homojunction improved the photocurrent and H 2 production. Carbon quantum dots (CQDs) are promising photosensitizers for photoelectrochemical (PEC) water splitting. In this work, biomass-derived CQDs were synthesized by a bottom-up approach using 13 precursors. Among them, cinnamaldehyde-, isoflavone-, and hydroxy-2,5-dimethyl-3(2H)-furanone-derived CQDs were selected for further tuning based on their relatively higher quantum yields (QYs), and acceptable yields. To tune the optical properties, three nitrogen sources, namely urea, m-phenylenediamine, and neutral red, were introduced, yielding blue-, green-, and red-emitting CQDs (B-CQDs, G-CQDs, and R-CQDs) with QYs of 13.20%, 20.40%, and 25.20%, respectively. Their absorption edges were located at 376, 470, and 579 nm, corresponding to bandgaps of 3.30, 2.64, and 2.14 eV. CQDs-sensitized titanium dioxide homojunction (THJ) photoelectrodes were fabricated via surface silanization. The R-CQDs/THJ photoelectrode achieved the highest photocurrent density among the three CQDs-decorated photoelectrodes during the water splitting process. The photocurrent density of the pure THJ photoelectrode was increased markedly from 1.45 mA cm −2 to 2.56 mA cm −2 with the decoration of R-CQDs, while the hydrogen evolution rate increased from 26.17 to 44.73 μmol cm -2 h −1 , corresponding to a 1.7-fold enhancement. This work provides insight into the relationship between the tunable optical properties of biomass-derived CQDs and their PEC sensitization behavior on TiO 2 photoelectrodes. The enhanced PEC performance is attributed to the combined effects of broadened spectral absorption and improved interfacial charge separation and transfer after decoration with CQDs. Download: Download high-res image (213KB) Download: Download full-size image