A hybrid GaN/Ga₂O₃ structure anchored on carbon cloth as a high-performance electrode of supercapacitors

A hybrid structure of GaN/Ga₂O₃ microrods was fabricated on carbon cloth (CC) using a hydrothermal process combined with a high-temperature nitridation followed by an air annealing process. By elevating the post-annealing temperature to 500 °C, both electron density (N_D) and specific capacitance (C_a) of the composite electrode were significantly enhanced. Symmetric SCs assembled with GaN/CC-500 showed great potential in both 1 M H₂SO₄ aqueous solution and a PVA-H₂SO₄ gel-like electrolyte. The aqueous symmetric GaN/CC-500 SC exhibited an excellent capacitance (1301.20 mF cm^-2, 0.5 mA cm^-2), high rate capability (75.23% of capacitance retention at 10 mA cm^-2), outstanding cycling stability (77.27% of capacitance retention after 20 000 cycles, 10 mA cm^-2), and large energy storage capability (27.53 μW h cm^-2 of energy density, 0.10 mW cm^-2 of power density). All-solid-state symmetric GaN/CC-500 SC also manifested a high capacitance (1183.35 mF cm^-2, 0.5 mA cm^-2) and good rate capability (53.98% capacitance retention, 10 mA cm^-2). The high electrochemical performance of the GaN/CC-500 electrode is attributed to the GaN/Ga₂O₃ hybrid structure, with α-Ga₂O₃ providing absorption/redox active sites on the surface, and the heavily oxygen-doped GaN enabling fast electron transport. The microrods with the GaN/Ga₂O₃ hybrid structure as the active material for solid SCs can deliver an energy density of 0.58 W h kg^-1 (3.54 mW h cm^-3) with a power density of 154 W kg^-1 (0.94 W cm^-3). The mechanism identified in this work would be helpful in designing GaN-based energy storage devices with better performances in the future.