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Owing to the inertness of CO2 molecules, the development of highly active photocatalysts for CO2 reduction reactions (CO2RR) remains a formidable challenge. Here, we designed an MXene-based single-atom Fe co-catalyst (Fe1/Ti3−xC2Ty) featuring fast Ti–Fe electron channels to achieve enhanced CO2RR performance. The synthesized Fe1/Ti3−xC2Ty exhibited a CO yield of 259.0 μmol g−1 h−1 without the addition of any organic sacrificial agents. The experimental and computational results reveal that, electrons transfer from Ti to Fe and then accumulate at the active sites, which facilitates the transfer of charges and enhances the activation of CO2 molecules. This work provides a new direction of MXene-based non-noble-metal monoatomic catalysts for efficient photoreduction of CO2 under gas–solid photocatalytic conditions with pure water. [ABSTRACT FROM AUTHOR]

Moderate B-doped Cuδ+ sites have outstanding performance for electrocatalytic NO3−-to-NH3. The faradaic efficiency can reach 96.8% with a current density of 26.3 mA cm−2 and an NH3 yield rate of 7.2 mg h−1 mgcat.−1. The active and stable Cuδ+ sites contribute to enhanced electron transport and higher reactivity. In situ experiments and theoretical calculations show that the Cuδ+ sites with moderate B-doping can decrease the reaction barrier and facilitate the formation of *NOH, leading to high catalytic activity for the NO3−-to-NH3 reaction. [ABSTRACT FROM AUTHOR]

Single-atom catalysts (SACs) regulated by heteroatoms have displayed great potential as electrocatalysts for highly efficient hydrogen evolution reaction (HER); however, the controllable synthesis of an axial coordination structure of SACs to achieve robust HER performance remains a great challenge. Herein, we have proposed a doping-adsorption-pyrolysis strategy to construct NiN4–Cl active sites with axial Cl coordination for accelerating electrocatalytic HER. The obtained NiN4–Cl SAs/NC catalyst exhibits superior HER activity with low over-potential, small Tafel slope, high turnover frequency, and long-term stability. Density functional theory calculation reveals that the excellent HER performance of NiN4–Cl SAs/NC originates from the axial Cl-coordination-induced electronic localization enhancement, which is beneficial for the adsorption and activation of H* intermediate, thus accelerating the HER process. This work opens a new opportunity for rational design and construction of high-performance SAC catalysts by axial coordination strategy for electrocatalytic application. [ABSTRACT FROM AUTHOR]

Selective oxidation of toluene to benzoic acid (BAC) with benign oxidant O2 is of great importance, but remains a great challenge, especially using non-noble metallic catalysts. In this work, the Co@N/Co-CNT catalyst, which was composed of atomically dispersed CoN4 species embedded in N-doped CNTs and encapsulated Co nanoparticles, was synthesized. The loading CoN4 could reach 6.4 wt%. It was found that the catalyst exhibited outstanding performance for selective aerobic oxidation of toluene to BAC without additives under solvent-free conditions. The selectivity of BAC could be as high as 91.6% at a toluene conversion of 33.5%, which is much higher than the value reported to date, including those over noble metal-based catalysts. The control experiments indicated that the main active species were CoN4 sites and the outstanding catalytic performance of Co@N/Co-CNTs can be attributed mainly to the unique properties of the CoN4 species and its high loading in the catalyst. Furthermore, the Co@N/Co-CNTs also had an excellent catalytic performance in the selective aerobic oxidation of xylenes to toluic acid derivatives. [ABSTRACT FROM AUTHOR]

Insights into the real catalytic active site(s) of promising oxygen evolution reaction (OER) catalysts is significant for the further development of high-performance catalysts. Spinel cobalt oxide (Co3O4), with both tetrahedral (Co2+) and octahedral (Co3+) sites, has been widely studied as an efficient non-precious OER catalyst. However, controversial results still exist regarding its OER performance in determining the active sites from two different tetrahedral and octahedral sites. Here, we have designed size-controllable Co3O4 hexagonal platelets with (111) exposed surfaces only containing tetrahedral Co2+ sites as model catalysts, and systematically investigated the catalytic properties of the tetrahedral sites on the surface of the (111) plane and the octahedral sites on the surface of the (110)-B plane for the OER using density functional theory (DFT) and various characterization methods. The theoretical and experimental results further reveal that the high catalytic activity is based on the existence of octahedral sites in Co3O4, meaning that the octahedral sites are responsible for the OER reaction and have been identified as the dominant active sites of spinel Co3O4. [ABSTRACT FROM AUTHOR]