Flexible nitrogen-doped carbon heteroarchitecture derived from ZIF-8/ZIF-67 hybrid coating on cotton biomass waste with high supercapacitive properties

The exploration of new-family flexible carbon architectures is significant with regard to flexible electrochemical capacitors. Herein we show the carbonization of core-shell structured metal-organic frameworks (MOFs) (i.e., ZIF-8@ZIF-67) on a waste biomass of cosmetic cotton to prepare flexible nitrogen-doped carbon heteroarchitectures (hetero-fNCs) that possess high supercapacitive properties, including a high energy density of 30 Wh kg at 1440 W kg and good capacitance retention of 89.5% after 5000 cycles. Our elaborately designed hetero-fNCs demonstrate multiple advantages: (i) The outer-layer ZIF-67-derived mesoporous carbons show abundant mesopores, providing abundant ion-diffusion pathways for mass transport and rich graphite microstructures, improving electrical conductivity for electron transfer; (ii) the inter-layer ZIF-8-derived microporous carbons possess a mass of micropores for more charge storage; (iii) the inner-layer cosmetic cotton-derived flexible carbons afford good mechanical flexibility, guaranteeing performance stability during use; and (iv) the plentiful nitrogen dopants within all carbon components increase the capacitance through their pseudocapacitive contribution. As a consequence, the flexible supercapacitor based on hetero-fNCs exhibits high energy and power densities, as well as good bending stability, highlighting the significance of MOFs and flexible biomass materials