Abstract: Cobalt-based oxides, with high abundance, good stability and excellent catalytic performance, are regarded as promising photocatalysts for artificial photosynthetic systems to alleviate foreseeable energy shortages and global warming. Herein, for the first time, a series of novel spongy porous CDs@CoO_x materials were synthesized to act as an efficient and stable bifunctional photocatalyst for water oxidation and CO₂ reduction. Notably, the preparation temperatures visibly influence the morphologies and photocatalytic performances of the CDs@CoO_x. Under the optimal conditions, a maximum O₂ yield of 40.4% and pretty apparent quantum efficiency (AQE) of 58.6% at 460 nm were obtained over CDs@CoO_x-300 for water oxidation. Similarly, the optimized sample CDs@CoO_x-300 manifests significant enhancement on the CO₂-to-CO conversion with a high selectivity of 89.3% and CO generation rate of 8.1 μmol/h, which is superior to most previous cobalt-based catalysts for CO₂ reduction. The composite CDs@CoO_x-300 not only exposes more active sites but also facilitates electron transport, which results in excellent photocatalytic activity. In addition, the boosted photocatalytic behavior is attributed to the synergistic effect between CoO_x and CDs, which was verified by the photocatalytic activity control experiments and electrochemical characterization. The work offers a novel strategy to fabricate a high performance bifunctional photocatalyst for water oxidation and CO₂ reduction.

Key words: Carbon dots coupled CoO_x, Bifunctional photocatalyst, Water oxidation, CO₂ reduction, Synergistic effect