Rational design of non-noble materials as highly efficient, economical, and durable bifunctional catalysts for oxygen evolution and reduction reactions (OER/ORR) is currently a critical obstacle for rechargeable metal-air batteries. A new route involving S was developed to achieve atomic dispersion of Fe-N species on N and S co-decorated hierarchical carbon layers, resulting in single-atom bifunctional OER/ORR catalysts for the first time. The abundant atomically dispersed Fe-N species are highly catalytically active, the hierarchical structure offers more opportunities for active sites, and the electrical conductivity is greatly improved. The obtained electrocatalyst exhibits higher limiting current density and a more positive half-wave potential for ORR, as well as a lower overpotential for OER under alkaline conditions. Moreover, a rechargeable Zn-air battery device comprising this hybrid catalyst shows superior performance compared to Pt/C catalyst. This work will open a new avenue to design advanced bifunctional catalysts for reversible energy storage and conversion devices.

The garnet-related oxides with the general formula Li 7Àx La 3 Zr 2Àx Ta x O 12 (0 # x # 1) were prepared by conventional solid-state reaction. X-ray diffraction (XRD), neutron diffraction and AC impedance were used to determine phase formation and the lithium-ion conductivity. The lattice parameter of Li 7Àx La 3 Zr 2Àx Ta x O 12 decreased linearly with increasing x. Optimum Li-ion conductivity in the Li-ion garnets Li 7Àx La 3 Zr 2Àx Ta x O 12 is found in the range 0.4 # x # 0.6 for samples fired at 1140 C in an alumina crucible. A room-temperature s Li z 1.0 Â 10 À3 S cm À1 for x ¼ 0.6 with an activation energy of 0.35 eV in the temperature range of 298-430 K makes this Li-ion solid electrolyte attractive for a new family of Li-ion rechargeable batteries.

With the unique-layered structure, MXenes show potential as electrodes in energy-storage devices including lithium-ion (Li ) capacitors and batteries. However, the low Li -storage capacity hinders the application of MXenes in place of commercial carbon materials. Here, the vanadium carbide (V C) MXene with engineered interlayer spacing for desirable storage capacity is demonstrated. The interlayer distance of pristine V C MXene is controllably tuned to 0.735 nm resulting in improved Li-ion capacity of 686.7 mA h g at 0.1 A g , the best MXene-based Li -storage capacity reported so far. Further, cobalt ions are stably intercalated into the interlayer of V C MXene to form a new interlayer-expanded structure via strong V-O-Co bonding. The intercalated V C MXene electrodes not only exhibit superior capacity up to 1117.3 mA h g at 0.1 A g , but also deliver a significantly ultralong cycling stability over 15 000 cycles. These results clearly suggest that MXene materials with an engineered interlayer distance will be a rational route for realizing them as superstable and high-performance Li capacitor electrodes.