Search

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 (ND) and specific capacitance (Ca) 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. [ABSTRACT FROM AUTHOR]

Abstract: Hydrothermal carbonization (HTC) process of biomass has showed many merits for the preparation of unique carbon-based material. To overcome the challenges of inherently low porosity and conductivity associated with HTC method-prepared carbons, herein a modified hydrothermal reaction was employed to prepare hierarchically porous carbon spheres (HPCS) with large surface area by using starch as carbon precursor and ammonium ferrous sulfate as porogen. The HPCS materials exhibit excellent electrochemical performance as active materials for electric double-layer capacitors, as demonstrated by a large specific capacitance of 248 F g−1 at 0.5 A g−1, a high volumetric capacitance of 181 F cm−3 at 0.5 A g−1, good capacity retention, and excellent cycling stability. The modified hydrothermal method proposed here is promising to prepare carbon materials for wide applications.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Biomass-derived porous carbons have been extensively investigated as potential electrode materials of electrochemical energy storage devices. Herein, hierarchical porous carbons with high specific surface area and large mesoporosity are successfully prepared from leftover rice, a common meal surplus, benefiting from its unique swelled structure and the activation effect of potassium hydroxide. The hierarchical porous carbons exhibit outstanding electrochemical energy storage performances in 1 M TEABF 4 /PC (propylene carbonate) electrolyte, including a high specific capacitance of 153.2 F g−1 at 0.2 A g−1 based on the active material, a high specific energy density of 22.6 Wh kg−1 at a power density of 21,503 W kg−1 based on the cells and over 87% capacitance retentions after 10,000 cycles at 1 A g−1. Such excellent electrochemical performances demonstrate that leftover rice can be potentially applied as bioresource for high property porous carbon electrode materials of supercapacitors. • Hierarchical porous carbons were prepared from leftover rice. • High surface area over 2,000 m2 g−1 and large volume over 1.8 cm3 g−1 were achieved. • A high energy density of 22.6 Wh kg−1 was maintained at 21,503 W kg−1 for supercapacitors. • Stable cycle performance was demonstrated after 10,000 cycles at 1 A g−1. [ABSTRACT FROM AUTHOR]

Abstract Carbon flakes with a specific surface area of 3010 m2 g−1, a pore volume of 2.756 cm3 g−1 and an ultrahigh mesoporous volumetric ratio of 97.6% were prepared from tubular kapok fibers through a simple low-temperature pre-carbonization and KOH activation process. The low-temperature pre-carbonization in air was effectively dewaxed the biomass and the thus obtained thin precursor was adequately wetted and etched by KOH, both of which might have resulted in the much improved textural properties. When used as electrode materials of symmetric supercapacitors in organic electrolyte, the carbon flakes displayed high energy density at high power density, e.g. 24 Wh kg−1 at 24,029 W kg−1, which was among the best values reported so far on biomass-derived porous carbon electrodes. The results reported in this work indicated that both the selection of bio-resources and pre-carbonization treatment were important for preparation of carbonaceous electrode materials with tailored texture properties and enhanced electrochemical energy storage performance. Highlights • Highly mesoporous carbon flakes were prepared from tubular-structured kapok fibers. • High mesoporous volumetric ratio of 97.6% towards a pore volume of 2.756 cm3 g−1 was achieved. • A low-temperature pre-carbonization in air was effective to dewax the kapok fibers. • The HMCFs exhibited high energy storage capacitance in organic electrolyte. [ABSTRACT FROM AUTHOR]

Porous carbon spheres with high specific surface area (2955 m 2 g − 1 ) and large pore volume (1.65 cm 3 g − 1 ) were prepared by incorporating boron in spherical polymeric precursors followed by reactive H 3 PO 4 activation. In such a process H 3 PO 4 acted as both an activating agent to activate the polymeric precursors and a reactant to extract out the pre-embedded boron from the carbonized spheres through formation of base dissolvable BPO 4 , hence generated additional pores in the carbon spheres and also widened the pore diameters. With these improved texture properties, the porous carbon spheres exhibited much enhanced energy storage capacities as electrode of symmetrical electrochemical capacitor in 1 M TEABF 4 /PC electrolyte. Energy densities of 31.3 and 20.3 Wh kg − 1 were obtained at power densities of 259 and 11,000 W kg − 1 (based on the active mass of both electrodes), respectively, which were much higher than those of the porous carbon spheres prepared without boron template and commercial activated carbons (YP-50F, Kuraray). This study provided a versatile strategy to tune the texture properties of porous carbons by combining element incorporation and reactive chemical activations, thus could be potentially used to fabricate high performance carbonaceous electrode materials for electrochemical energy storage devices. [ABSTRACT FROM AUTHOR]