N-doped-carbon/cobalt-nanoparticles/N-doped-carbon multi-layer sandwich nanohybrids derived from cobalt-MOF of 3D molecular structure for bifunctional electrocatalysts toward on-chip solid-state Zn-air batteries
The unsatisfactory energy efficiency and leakable liquid electrolyte in conventional Zn-air batteries of intrinsic semi-open structure greatly blunts their opportunity to be safe micropower source for flexible/wearable electronics. Herein, N-doped-carbon/cobalt-nanoparticles/N-doped-carbon (NdC-CoNPs-NdC) multi-layer sandwich nanohybrids were first synthesized via pyrolysis of a well-designed Co-MOF precursor with 3D molecular framework. Profiting from the synergistic effect enabled by the interlayer-confined growthed monodispersed cobalt nanoparticles of high activity/stability and thousand-layer-cake porous N-self-doped carbon skeleton of high conductivity and additional active sites, as well as the reasonable design of multi-layer sandwich interface structure between them that act as interconnected nanoreactors, the as-obtained NdC-CoNPs-NdC multi-layer sandwich nanohybrids exhibits excellent bifunctional catalytic activity of a small ORR/OER subtraction (0.83 V). Followed a planar electrode configuration design with the interdigital carbon cloth coated with NdC-CoNPs-NdC as air-cathode and interdigital Zn-foil as metal-anode, as well as introduction of polyacrylamide-co-polyacrylic/6M KOH alkaline gel as incombustible solid-state electrolyte, on-chip all-solid-state rechargeable Zn-air batteries (OAR-ZABs) are further developed, achieving a cycle life up to 150 cycles/50 h, a high power density/specific capacity as much as 57.0 mW cm-2/771 mA h g-1, and excellent coplanar integration capability and mechanical flexibility for wording steadily under bending deformation. Eventually, as an additional advance, an autonomous smart watch powered by the coplanar integrated OAR-ZABs is demonstrated, which possesses excellent integrity and flexibility, and can be comfortably wearable for timing and steps counting dynamically, demonstrating the successful application in assembling OAR-ZABs into highly integrated wearable electronics for compatible micropower source.