Boosted CO₂ photoreduction to methane: Via Co doping in bismuth vanadate atomic layers

CO₂ photoreduction to valuable hydrocarbons is attractive and promising. Nevertheless, the photoactivity has been pretty low to date, and deeper insights into improving CO₂ conversion efficiency remain a challenge. Here, BiVO₄ atomic layers have been synthesized as ideal platforms to investigate the correlation between the electronic structures and activities for CO₂ photoreduction. Cobalt (Co) is then deliberately doped in BiVO₄ atomic layers to adjust the electronic structures. XPS analysis, CO₂ TPD and electrochemical experiments indicate that Co doping makes the electron densities around O anions increase, which could likely facilitate CO₂ activation and electron transfer to CO₂ molecules, while photoelectrochemical and photocatalytic oxygen evolution experiments demonstrate that Co doping could also promote water oxidation reactions. Further investigations by density functional theory calculation reveal that Co doping results in the generation of new defect levels above the Fermi level, inferring that a higher hole concentration is favorable for water oxidation, and the doped Co 3d orbits located at the top of valence bands might serve as active centers for water oxidation. As a result, Co-doped BiVO₄ atomic layers achieve an efficient and stable CH₄ production rate of 23.8 μmol g^-1 h^-1 under atmospheric CO₂ concentration (400 ppm), which is about three times the activity of pristine BiVO₄ atomic layers. This work might help to gain deeper insights into the design of CO₂ photoreduction catalysts.