Regulating the crystallinity and hydrophobicity of cobalt boride nanosheet for enhanced CO2 photoreduction performance

•A facile thermal-processed post-treatment is used to prepare CoB nanosheets.•CoB cocatalyst delivers a high CO formation rate of 29.6 μmol h−1.•The enhanced performance can be attributed to the promoted crystallinity and hydrophobicity. Developing low-cost and efficient cocatalysts to strengthen CO2 conversion using solar energy is of great importance to reduce reliance on fossil fuels. Two-dimensional cobalt boride (CoB) nanosheets with comparatively high work function and low ΔGH* are prone to undergo low crystallinity under rigorous synthetic conditions. Herein, a facile method of thermal-induced molten salt melt is used to regulate the structure characters of CoB nanosheets. The optimized CoB cocatalyst as a noble-metal-free cocatalyst delivers a high CO formation rate of 29.6 μmol h−1 and selectivity of 70.1 % with visible light irradiation. This elevation is steered by the promoted crystallinity and hydrophobicity, which can speed the charge kinetics and reduce the proton accumulation on the surface as evidenced by various photoelectrochemical tests and contact angle tests of water, respectively. The high CO2 adsorption based on alkaline Co atoms of the CoB nanosheets drives the key COOH* intermediates production analyzed by the in-suit infrared spectra. This work exploits newly Co-based cocatalysts and strengthens the structure–activity relationship for efficient CO2 photoconversion.