Tuning the active plane and crystallinity of GaN microcrystals for high-performance supercapacitors through potassium nitrate-mediated synthesis

The surface atomic structure and crystallinity have an important effect on the electrochemical energy storage of electrode materials, in addition to the surface chemistry and textural properties. We report here for the first time that the surface atomic structure and crystallinity of GaN, a renowned electrode material for energy storage, can be tuned by controlling the annealing time via potassium nitrate-mediated synthesis. The underlying mechanism for GaN microcrystals with enhanced intensity ratios of and manifesting excellent rate performance has been revealed by theoretical computations. The energy storage mechanism and electrode kinetics of the GaN electrodes have been clarified. In addition, the GaN microcrystals-based symmetric supercapacitors empowered by 52 wt% HPO can deliver an output voltage of 1.5 V and volumetric specific energy of 11.6 and 40.2 W h L at a specific power of 392.2 W L when operating at −60 and 60 °C, respectively, with electrode material on a commercial loading level.