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We successfully construct noble-metal-free cobalt nitride/nitrogen-rich carbons (Co 4 N/NCs) catalysts by a photochemical assembly strategy. The obtained Co 4 N/NCs catalysts show extraordinary activity for CO 2 -to-CO reduction. The highest turnover frequency per cobalt atom within Co 4 N/NCs reaches 6.7 s-1. • Cobalt nitride/nitrogen-rich carbons (Co 4 N/NCs) are prepared by a photochemical approach. • The Co 4 N/NCs is an effective catalyst for CO 2 reduction. • The quantum yield for CO production over the Co 4 N/NCs reaches 7.2% at 450 nm. Utilizing solar energy to convert CO 2 into fuels and chemicals represents a promising solution to reduce reliance on fossil fuels, but it is hampered by the lack of highly-efficient catalysts. Herein, we report unique cobalt nitride/nitrogen-rich carbons (Co 4 N/NCs), which can work as noble-metal-free catalysts for CO 2 -to-CO conversion. The mass activity of Co 4 N/NCs is two orders of magnitude higher than those of previously reported CO 2 photoreduction catalysts. The quantum yield for CO production at 450 nm reaches 7.2% with a turnover frequency per Co atom of 0.97 s-1. The electronic structure and coordinated environment of catalysts are analyzed by X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy. The reaction processes are investigated by in-situ diffuse reflectance infrared fourier transform spectroscopy and density functional theory calculations. Results suggest that the synergetic effects between the Co 4 N and the NCs can consolidate the adsorption and activation of CO 2 and accelerate the interfacial electron-transfer kinetics between the Co 4 N/NCs catalysts and light-harvesting antenna, thereby resulting in the outstanding activity for synthesizing CO from CO 2. This work offers the possibility to design Co-based host-guest topology for highly-efficient CO 2 reduction. [ABSTRACT FROM AUTHOR]

The nitrogen vacancies on the carbon nitride surface can function as active sites to catalyze water oxidation reaction, while preventing recombination of the electron/hole pairs, thus accelerating the reaction kinetic of oxygen photosynthesis. • A photocarving strategy is first employed to create nitrogen vacancies (NVs) on the surface of polymeric carbon nitride (PCN). • The embedded NVs can function as active sites to catalyze oxygen evolution reaction (OER), thereby accelerating the sluggish kinetic of OER. • The embedded NVs can effectively promote the separation and transfer of the photogenerated charge carrier. • The PCN-NVs without any extra metal cocatalyst assistance exhibits a 4.2-fold increase in the oxygen photosynthesis activity compared with pristine PCN. Photocatalytic water splitting necessitates robust cocatalysts to accelerate the oxygen evolution reaction (OER). However, most OER cocatalysts are based on noble metal oxides. Besides, the loose interface between semiconductor and cocatalyst results in inefficient charge transfer. The fabrication of photocatalysts with integrated light-harvesting and catalytic centers for OER is therefore desired. Herein, we provide a photocarving strategy to create nitrogen vacancies (NVs) on polymeric carbon nitride (PCN). It is confirmed that the embedded NVs can function as active sites to catalyze OER, while promoting the transfer of the photogenerated charge for OER. As a result, PCN-NVs without any extra noble-metal cocatalyst assistance exhibit an enhanced oxygen evolution rate compared with the pristine PCN. Additionally, the PCN obtained from other precursors can also be engineered by this photocarving method, while promoting oxygen photosynthesis. This work provides an avenue to design light-transducers with combined light-harvesting and catalytic configurations for oxygen synthesis chemistry. [ABSTRACT FROM AUTHOR]