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α-Ga2O3 microrods was deposited on carbon cloth (CC) using a hydrothermal process followed by a high-temperature annealing in air. The microstructure of the obtained Ga2O3/CC composite electrodes were characterized with scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Their electrochemical performances were tested with electrochemical impedance spectroscopy (EIS), Mott-Schottky (MS), cyclic voltammetry (CV) and galvanostatic charge/discharge techniques (GCD). By comparing the electron densities and mobilities of the Ga2O3/CC electrodes prepared with different hydrothermal durations, the doping mechanisms of point defects in α-Ga2O3 were revealed. The point defects in α-Ga2O3 including Ga-oxygen vacancies (Ga-VO), gallium vacancies (VGa), and VGa-VO complexes were all identified as the scattering centers. By extending the hydrothermal duration to more than 6 h, the electronic conductivity of the Ga2O3/CC electrode was enhanced by reducing the number of point defects in α-Ga2O3. The Ga2O3/CC-6h aqueous symmetrical supercapacitor (SC) showed a remarkable increase in the electrochemical performance by exhibiting a specific areal capacitance of 1394 mF cm−2 at 0.5 mA cm−2, with 67% of the capacitance retained when the current density was increased to 20 mA cm−2, and 76.5% of capacitance retention after 20,000 cycles under a current density of 10 mA cm−2. The point defect mechanism identified in the article would pave the way to develop novel energy storage devices based on α-Ga2O3 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]

Novolacs phenolic-resin (PF) was easily polycondensed into polymeric powders with sizes and morphologies ranging from microspheres to nanoparticles by a simple solvothermal process without adding any crosslinking agent. Activating the highly divided PF powders by CO resulted in nanosize activated carbons with high specific surface area (2092 m g) and large pore volume (1.33 cm g) while preserving a high carbon yield of about 38 wt%. As for adsorption tests, the micropore-dominated activated nanocarbons exhibited fast and high adsorption capabilities towards both Cr(VI) ions and bulky rhodamine B molecules due to their much improved external surface area and the greatly shortened intra-particle diffusion distance. The equilibrium adsorption amounts of Cr(VI) and RB on the activated nanocarbons as estimated by the Langmuir model were 200 and 990 mg g, achieved within an adsorption time of 30 and 360 min, respectively. [ABSTRACT FROM AUTHOR]