Monitoring Electron Flow in Nickel Single-Atom Catalysts during Nitrogen Photofixation

An efficient catalytic system for nitrogen (N2) photofixation generally consists of light-harvesting units, active sites, and an electron-transfer bridge. In order to track photogenerated electron flow between different functional units, it is highly desired to develop in situ characterization techniques with element-specific capability, surface sensitivity, and detection of unoccupied states. In this work, we developed in situ synchrotron radiation soft X-ray absorption spectroscopy (in situ sXAS) to probe the variation of electronic structure for a reaction system during N2 photoreduction. Nickel single-atom and ceria nanoparticle comodified reduced graphene oxide (CeO2/Ni-G) was designed as a model catalyst. In situ sXAS directly reveals the dynamic interfacial charge transfer of photogenerated electrons under illumination and the consequent charge accumulation at the catalytic active sites for N2 activation. This work provides a powerful tool to monitor the electronic structure evolution of active sites under reaction conditions for photocatalysis and beyond.