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Melamine-assisted pyrolytic synthesis of core–shell cobalt@carbon nanotubes as efficient bifunctional electrocatalyst for rechargeable zinc–air batteries.

As potential alternatives to Pt-based catalysts for oxygen reduction reaction (ORR), iron (Fe)-based single-atomic site catalysts (SACs) have shown superior performances compared with others. For Fe SACs, the effect of directly coordinating N atoms has received intensive discussion, yet by contrast, the effect of secondary coordinating atoms has been left largely unexplored. Here, we developed a route to tuning externally doped N around Fe SACs to boost ORR activity. Density functional theory (DFT) calculations established the four different models for FeN4for ORR, indicating that the FeN4-PR-GN (pyrrolic-N for the first coordination shell and graphitic-N for the second coordination shell) can effectively improve the ORR performance. On the basis of theoretical calculations, we developed a two-step strategy including interior encapsulation and surface adsorption, which helped to regulate the different external coordination N of Fe SACs. The best-performing catalyst, FeN4-PR-GN, displays excellent ORR performances in alkaline electrolytes; in particular, the catalyst gives a half-wave potential of 0.92 V (vs.RHE) and high stability, which is much better than those of commercial Pt/C. Our work here not only demonstrates an efficient catalyst to boost ORR performances, but also develops a facile strategy for the preparation of SACs for advanced fuel cells.

The electrochemical reduction of CO2could play an important role in addressing climate-change issues and global energy demands as part of a carbon-neutral energy cycle. Single-atom catalysts can display outstanding electrocatalytic performance; however, given their single-site nature they are usually only amenable to reactions that involve single molecules. For processes that involve multiple molecules, improved catalytic properties could be achieved through the development of atomically dispersed catalysts with higher complexities. Here we report a catalyst that features two adjacent copper atoms, which we call an ‘atom-pair catalyst’, that work together to carry out the critical bimolecular step in CO2reduction. The atom-pair catalyst features stable Cu10–Cu1x+pair structures, with Cu1x+adsorbing H2O and the neighbouring Cu10adsorbing CO2, which thereby promotes CO2activation. This results in a Faradaic efficiency for CO generation above 92%, with the competing hydrogen evolution reaction almost completely suppressed. Experimental characterization and density functional theory revealed that the adsorption configuration reduces the activation energy, which generates high selectivity, activity and stability under relatively low potentials.

The title compound is synthesized from an aqueous solution of hydrous titanium oxide and lithium hydroxide (autoclave, 180 °C, 24 ) followed by calcination of the obtained powder at 400 °C for 2 h in air.