Co_(3)O_(4)/Mn_(3)O_(4) hybrid catalysts with heterointerfaces as bifunctional catalysts for Zn-air batteries

Zinc-air batteries(ZABs) with high energy density and safety are promising as next-generation energy storage systems, while their applications are severely hindered by the sluggish reaction kinetic of air cathodes. Developing a bifunctional catalyst with high activity and durability is an effective strategy to address the above challenges. Herein, a Co_(3)O_(4)/Mn_(3)O_(4) nanohybrid with heterointerfaces is designed as advanced cathode catalyst for ZABs. Density functional theory calculations show the heterogeneous interface between Co_(3)O_(4)/Mn_(3)O_(4) can improve the dynamics of carrier transport and thus enhancing the catalytic activity and durability. The Co_(3)O_(4)/Mn_(3)O_(4) catalyst anchored on reduced graphene oxide(rGO)exhibits high oxygen reduction reaction(ORR) activity with a half-wave potential of 0.86 V, and excellent oxygen evolution reaction(OER) activity with the potential of 1.59 V at 10 mA cm^(-2) , which are comparable to the commercial noble metal catalysts. The improved ORR/OER catalytic activity is ascribed to the synergistic effect of heterointerfaces between Co_(3)O_(4) and Mn_(3)O_(4)as well as the improved conductivity and contact area of oxygen/catalysts/electrolytes three-phase interface by r GO. Furthermore, a home-made ZAB based on Co_(3)O_(4)/Mn_(3)O_(4)/r GO shows a high open circuit voltage of 1.54 V, a large power density of 194.6 mW cm^(-2) and good long-term cycling stability of nearly 400 h at 5 mA cm^(-2) , which affords a promising bifunctional oxygen catalyst for rechargeable ZABs.

Revealing the surface atomic arrangement of noble metal alkane dehydrogenation catalysts by a stepwise reduction-oxidation approach

Surface characterization of metal nanoparticles is a critical need in nanocatalysis for in-depth understanding of the structure-function relationships.The surface structure of nanoparticles is often different from the subsurface,and it is challenging to separately characterize the surface and the subsurface.In this work,theoretical calculations and extended X-ray absorption fine structure(EXAFS)analysis illustrate that the surface atoms of noble metals(Pt and Pd)are oxidized in the air,while the subsurface atoms are not easily oxidized.Taking advantage of the oxidation properties,we suggest a stepwise reduction-oxidation approach to determine the surface atomic arrangement of noble metal nanoparticles,and confirm the rationality of this approach by identifying the surface structure of typical 2-3 nm Pt and Pd nanoparticles.The reduction-oxidation approach is applied to characterize the surface structure of model Pd-Sb bimetallic catalyst,which illustrates that the surface Pd is well isolated by Sb atoms with short bond distance at 2.70Å,while there are still Pd-Pd bonds in the subsurface.Density functional theory(DFT)calculations and Pd L edge X-ray absorption near edge structure(XANES)indicate that the isolation of surface Pd significantly decreases the adsorption energies of Pd-hydrocarbon,which leads to the high propylene selectivity and turnover frequency Pd-Sb bimetallic catalyst for propane dehydrogenation.