Amorphous CoO coupled carbon dots as a spongy porous bifunctional catalyst for efficient photocatalytic water oxidation and CO2 reduction

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@CoOx 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@CoOx. 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@CoOx-300 for water oxidation. Similarly, the optimized sample CDs@CoOx-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@CoOx-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 CoOx 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.