Thermal instability-induced formation of hierarchically structured porous GaN/nitrogen-doped carbon with high performance for supercapacitor

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Electrode materials with high specific surface area (SBET) and high stacking density face a dilemma, making it difficult for supercapacitor electrodes to simultaneously exhibit high areal discharge specific capacitance (Ca,dis) and high volumetric discharge specific capacitance (Cv,dis). By exploiting the high stacking density and thermal instability of metal (after group VIB) nitrides, an electrode material of GaN honeycombs/nitrogen-doped carbon is achieved that simultaneously exhibits high Ca,dis (730 mF cm−2) and Cv,dis (251 F cm−3) at 200 mF cm−2 and manifests a linear relationship between Ca,dis and electrode loading ranging from 3.4 to 7.6 mg cm−2. The GaN honeycomb-based symmetric supercapacitors can deliver high areal/volumetric specific energy of 21.8 μW h cm−2/3.12 mW h cm−3 at 5 mW cm−2/714.3 mW cm−3 after 20,500 cycles at varied current densities from 10 to 50 and then to 10 mA cm−2. The high performance of the GaN honeycomb-based electrodes is attributed to the synergistic effect of high SBET (378.3 m2 g−1), suitable pore sizes (concentrated at 1.4 nm), surface capacitive effect, and promoted kinetics of the faradaic reaction, due to the hierarchical structure combining the high SBET and fast kinetics of nanomaterials with the high stacking density of micron materials.