Oxygen vacancy associated single-electron transfer for photofixation of CO2 to long-chain chemicals.

The photofixation and utilization of CO2 via single-electron mechanism is considered to be a clean and green way to produce high-value-added commodity chemicals with long carbon chains. However, this topic has not been fully explored for the highly negative reduction potential in the formation of reactive carbonate radical. Herein, by taking Bi2O3 nanosheets as a model system, we illustrate that oxygen vacancies confined in atomic layers can lower the adsorption energy of CO2 on the reactive sites, and thus activate CO2 by single-electron transfer in mild conditions. As demonstrated, Bi2O3 nanosheets with rich oxygen vacancies show enhanced generation of •CO2- species during the reaction process and achieve a high conversion yield of dimethyl carbonate (DMC) with nearly 100% selectivity in the presence of methanol. This study establishes a practical way for the photofixation of CO2 to long-chain chemicals via defect engineering.

Highly Active Fe Sites in Ultrathin Pyrrhotite Fe7S8 Nanosheets Realizing Efficient Electrocatalytic Oxygen Evolution.

Identification of active sites in an electrocatalyst is essential for understanding of the mechanism of electrocatalytic water splitting. To be one of the most active oxygen evolution reaction catalysts in alkaline media, Ni-Fe based compounds have attracted tremendous attention, while the role of Ni and Fe sites played has still come under debate. Herein, by taking the pyrrhotite Fe7S8 nanosheets with mixed-valence states and metallic conductivity for examples, we illustrate that Fe could be a highly active site for electrocatalytic oxygen evolution. It is shown that the delocalized electrons in the ultrathin Fe7S8 nanosheets could facilitate electron transfer processes of the system, where d orbitals of FeII and FeIII would be overlapped with each other during the catalytic reactions, rendering the ultrathin Fe7S8 nanosheets to be the most efficient Fe-based electrocatalyst for water oxidation. As expected, the ultrathin Fe7S8 nanosheets exhibit promising electrocatalytic oxygen evolution activities, with a low overpotential of 0.27 V and a large current density of 300 mA cm-2 at 0.5 V. This work provides solid evidence that Fe could be an efficient active site for electrocatalytic water splitting.

Delocalized Spin States in 2D Atomic Layers Realizing Enhanced Electrocatalytic Oxygen Evolution.

The electrocatalytic activity of transition-metal-based compounds is strongly related to the spin states of metal atoms. However, the ways for regulation of spin states of catalysts are still limited, and the underlying relationship between the spin states and catalytic activities remains unclear. Herein, for the first time, by taking NiII -based compounds without high or low spin states for example, it is shown that their spin states can be delocalized after introducing structural distortion to the atomic layers. The delocalized spin states for Ni atoms can provide not only high electrical conductivity but also low adsorption energy between the active sites and reaction intermediates for the system. As expected, the ultrathin nanosheets of nickel-chalcogenides with structural distortions show dramatically enhanced activity in electrocatalytic oxygen evolution compared to their corresponding bulk samples. This work establishes new way for the design of advanced electrocatalysts in transition-metal-based compounds via regulation of spin states.