Activated carbon nanofibers (ACFs) with high specific surface area, excellent conductivity, and narrow pore‐size distribution, are regarded as a promising electrode material for high‐performance supercapacitors (SCs). Herein, a facile route to synthesize large‐scale amorphous CF (a‐CF) using catalytic pyrolysis of acetylene (C2H2) at 260 °C over copper catalysts is reported. The conversion rate of acetylene into a‐CF is estimated as high as 72.05 wt%. Subsequently, the as‐prepared a‐CF is transformed into ACFs by potassium hydroxide (KOH) at 800 °C with high specific surface area and porous structures. Moreover, nitrogen‐doped ACFs are conducted in the activation step through a physical mixing of a‐CF/KOH/melamine with various ratios. For SCs, the as‐prepared N‐ACFs display excellent specific capacitance and cycle stability. In the three‐electrode system, the N‐ACF (CF‐03) demonstrates a specific capacitance value of 227 F g−1 at 0.5 A g−1, and shows a 94% capacitance retention after a long cycle (10 000 cycles) at 2 A g−1. Moreover, the CF‐03‐based two‐electrode SC demonstrates a high energy density of 14.30 Wh kg−1 and a high power density of 79.88 W kg−1 in 1 m Na2SO4 electrolyte. Herein, a simple and promising way to prepare large‐scale a‐CF, ACF, and N‐doped ACFs is demonstrated.

Although highly porous carbon electrode materials from biomass wastes for high-performance electric double-layer capacitors (EDLCs) have attracted great attention recently, the fast charge−discharge performance under ultrahigh current density (100 A g −1 ) still remains a challenge. Herein, we develop a promising route to massively prepare honeycomb-like activated carbon (AC) with hierarchical porous features from spent lotus stems (SLSs) exhibiting an ultrahigh specific surface area of 4190 m 2 g −1 . The preparation process of the SLSAC samples includes carbonization at 400 °C in argon (denoted as c-SLS) and followed a KOH chemical activation using various KOH/c-SLS mass ratios at 800 °C for 1 h. The SLSAC-5-based electrode (KOH/c-SLS = 5/1) displays a good gravimetric capacitance of 330 F g −1 at 0.5 A g −1 with a superior high-rate capacitance of 243 F g −1 at 100 A g −1 and presents remarkable cycling stability with a capacitance retention near 100% over 10,000 cycles at 2 A g −1 using 6 M KOH aqueous electrolyte. Additionally, the SLSAC-5-based sample delivers an energy density of 18.6 W h kg −1 at 199.2 W kg −1 with 1 M Na 2 SO 4 electrolyte. Herein, we reveal a simple, promising route to massively generate SLSAC-based samples and investigate prominent electrochemical properties in ultra-fast charge−discharge EDLCs.

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Conducting atomic force microscopy and scanning surface-potential microscopy have been applied to image the surfaces of Mg-In-codoped GaN films grown by low-pressure metal-organic chemical-vapor deposition. Biscyclopentadienylmagnesium ͑CP 2 Mg͒ and trimethylindium ͑TMIn͒ have been used as the codoping sources in the experiment. The dislocation density at the film surface reduces to the lowest level ͑ϳ1.0ϫ 10 9 cm −2 ͒ when the TMIn/ CP 2 Mg flow rate ratio is about 1. The dislocation density tends to rise when the flow ratio increases, and carriers of the film accumulate near the rim of the dislocation at an accelerated speed. The work function of dislocation is also found lower than that of nondislocation areas. Such electrical unevenness may seriously influence the light emission of the component, which should not be ignored during fabrication and deserves careful attention.