Carbon quantum dots (CQDs) were synthesized by a facile and green pyrolysis method. The as-prepared CQDs show wide light absorption, tunable downconversion photoluminescence (PL) properties and excellent "upconversion" luminescence properties. CQDs were used to design the TiO2/CdS/C photoelectrodes for photoelectrochemical hydrogen evolution. The role of the CQDs was investigated based on the TiO2/CdS/C photoelectrodes. The results reveal that CQDs can enhance light-harvesting efficiency and improve their charge separation and transfer properties when coupled with conventional QD-sensitized photoelectrodes. Nevertheless, the contribution of "upconversion" luminescence of CQDs to the enhanced photoelectrochemical performance is negligible. (C) 2018 Elsevier Inc. All rights reserved.