3D hierarchical porous nitrogen-doped carbon/Ni@NiO nanocomposites self-templated by cross-linked polyacrylamide gel for high performance supercapacitor electrode

Three-dimensional nitrogen-doped carbon network incorporated with nickel@nickel oxide core-shell nanoparticles composite (3D NC/Ni@NiO) has been facilely prepared, self-templated by the cross-linked polyacrylamide aerogel precursor containing NiCl₂. Characterizations reveal that the Ni@NiO nanoparticles distribute homogeneously in the 3D nitrogen-doped carbon matrix and the composite is of hierarchical porous structure. When used as supercapacitor electrode in a three-electrode system, the 3D NC/Ni@NiO exhibits enhanced electrical conductivity and excellent electrochemical performance, presenting a high specific capacitance (389F g^-1 at 5 mV s^-1), good rate capability (276 F g^-1 at 100 mV s^-1) and outstanding cycling performance (with the capacitance retention of 70.2% after 5000 charge-discharge cycles). This is due to the synergistic effects of conductive metallic nickel, pseudocapacitive nickel oxide as well as in situ nitrogen doping of carbon network. Moreover, an asymmetric supercapacitor (ASC) was fabricated with NC/Ni@NiO as positive electrode and active carbon as negative electrode. The ASC device exhibits a maximum energy density of 19.4 W h kg^-1 at a power density of 700 W kg^-1 and shows good cycling stability (73.8% capacity retention after 3000 cycles), indicating that it has great promise for practical energy storage and conversion application.