Biomass chitin-derived honeycomb-like nitrogen-doped carbon/graphene nanosheet networks for applications in efficient oxygen reduction and robust lithium storage

Three-dimensional honeycomb-like nitrogen-doped carbon nanosheet/graphene (N-DC/G) nanonetwork films were prepared successfully by dissolution and coagulation of chitin and graphene oxide in NaOH/urea aqueous solution using a repeated freezing-thawing process and a solution pre-gelation method, and then high-temperature carbonization under an Ar atmosphere. Subsequently, the resulting honeycomb-like N-DC/G films exhibited homogeneous interconnected open-cell architectures with the average pore size of about 2 mu m, and the graphene nanosheets were homogeneously dispersed and immobilized in the nitrogen-doped carbon nanosheet matrix. The porous N-DC/G films combined the advantages of high conductivity of graphene, abundant defects and favorable nitrogen species, and the porous structure of carbons, which endowed them with excellent catalytic activity with an onset potential of -0.07 V and a kinetic current density of 4.64 mA cm(-2) at -0.7 V superior to that of pure N-DC and commercial Pt/C electrodes, making them high-performance metal-free electrocatalysts for oxygen reduction. As binder-free, integrated anodes for lithium-ion batteries (LIBs), the free-standing N-DC/G films exhibited appealing electrochemical lithium storage properties with a high reversible capacity (798.86 mA h g(-1)) even after 300 cycles at 500 mA g(-1) and a capacity retention of 94.21%. Therefore, we opened up a completely new avenue for the large-scale fabrication of light-weight, highly effective, and low-cost N-doped carbon-based energy storage materials, broadening the applications of chitin.