Transformation of Biomass Precursor into Both High‐Efficiency Cathode Catalyst and Solid Electrolyte for Rechargeable Zn‐Air Batteries

Cattail grass biomass is used as the precursor for preparing both bi-functional cathode catalyst and solid electrolyte in the construction of high-performance Zn-air battery (ZAB). First, cattail grass is transformed into porous carbon micron tubes (CMTs), which are immobilized by polyoxometalate clusters of (H₂bimb)₃ {Cd(P₄Mo₆O₃₁H₈)₂}·5.5H₂O (bimb = 4,4-di(1H-imidazole-1-yl)-1,1-biphenyl) (abbreviation: {Cd(P₄Mo₆)₂}), and then calcinated in N₂ to form Mo₂C-MoO₂/CMTs. {Cd(P₄Mo₆)₂} not only acts as the Mo source for the formation of Mo₂C-MoO₂ heterojunction but also provides the Mo species to in situ etch carbon tubes to generate the porous microstructures. In ZABs, the multi-catalytic sites (Mo₂C and MoO₂) can both facilitate the oxygen reduction / evolution reaction (ORR/OER) catalytic performance at the battery cathode, and inhibit the formation of zinc dendrites by forming a large number of nucleation sites on the battery anode. Density Functional Theory results have verified the synergistic effect between Mo₂C and MoO₂, indicating that multiple active sites with superior catalytic effect than the individual materials. The ZABs assembled with Mo₂C-MoO₂/CMTs exhibit a peak power density of 264.09 mW cm^-2. Cattail grass is also used to prepare highly conductive gel electrolyte to assemble all-solid coin cell ZABs with high capacity of 97.33 mW cm^-2 and 100 h of charge-discharge stability.