Fig. 3From: Progress of carbon-based electrocatalysts for flexible zinc-air batteries in the past 5 years: recent strategies for design, synthesis and performance optimizationa (i) Free-energy diagram of the ORR over Co2P and Cu-doped Co2P surfaces. The different charge densities of (ii) Co2P (121) and (iii) Cu-doped Co2P (121). The blue and red regions separately indicate the depletion and accumulation of electrons [22]. b Illustration of the synthesis procedure of the Od-Mn3O4@CNA/CC nanostructure, and its formation mechanisms at atomic scale. The blue, pink, gray and yellow spheres represent the Mn, O, C and Od atoms, respectively [46]. c (i) Supercell model of Mn3O4. (ii) Mn–O octahedral and pyramidal crystal fields and the d-orbital splitting configurations. (iii) Electron density differences of Od-Mn3O4 (pink circle represents Mn3+, sky blue circle represents Mn2+) [47]. d Synthesis and morphological characterization of NB-CN [52]. (i) Illustration of the formation mechanism of the graphitic carbon nanocage. (ii) SEM image and (iii) TEM image of NB-CN. (iv) HR-TEM image of NB-CN before acid washing and (v) HR-TEM image of NB-CN. e Optimized adsorption structures of the ORR intermediates and CO on BGNR [54]: (i) O2, (ii) OOH, (iii) O, (iv) H, (v) OH, (vi) H2O and (vii) CO. f Schematic diagram of the synthetic process of the Co3O4@NiFe LDH hybrid nanowire arrays on Ni foam and flexible carbon cloth, respectively [24]. g Schematic illustration of Zn- Ni3S2 battery and zinc-air battery and structure diagram of Ni3S2 molecular, respectively [23]Back to article page