Abstract
Commercial coconut shell-based activated carbon (CSAC) has low specific capacitance and specific capacitance retention owing to its undeveloped pore structure and low proportion of heteroatoms. In this study, dielectric barrier discharge plasma was used to enhance the specific capacitance and rate capability of CSAC. H2O was used as an excited medium to introduce oxygen functional groups. The physico-chemical properties of CSAC and CSAC modified by H2O plasma (HCSAC) were revealed by automated surface area and pore size analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Electrochemical work was applied to investigate the electrochemical properties of CSAC and HCSAC. The results obtained showed that plasma modification improved the specific capacitance of CSAC by 64.8% (current density, 1 A g−1; electrolyte, 6 M KOH solution) within 100 s. This result is ascribed to the oxygen functional groups introduced to the surface of CSAC. It can also improve the hydrophilicity and wettability of the carbon surface leading to an increase from 76.7% to 84.6% in specific capacitance retention. Furthermore, H2O plasma modification can introduce oxygen functional groups without destroying the initial pore structures of CSAC. In summary, we provide a simple, fast, environment-friendly modification method to enhance the electrochemical properties of CSAC.
Highlights
In recent years, biomass-based activated carbon with a well-developed porosity and high specific surface has been widely applied in electrode materials for the production of supercapacitors [1,2]
Previous studies have found that etching the surface layer of activated carbon using dielectric barrier discharge (DBD) plasma resulted in an increase in the capacitance, which is mostly attributed to the creation of functional groups on the surface [7,11,12]
It can be seen from table 1 that coconut shell-based activated carbon (CSAC) and HCSAC that mainly consist of mesopores, and rapid DBD plasma etching process, lead to slight improvement on the Brunauer –Emmett–Teller (BET) surface area of the samples
Summary
Biomass-based activated carbon with a well-developed porosity and high specific surface has been widely applied in electrode materials for the production of supercapacitors [1,2]. A variety of modifications, including wet or gas oxidation, supercritical fluids, electrochemical oxidation, ion or cluster bombardment and plasma modification and activated carbon modification, have been applied to achieve higher electrochemical capacitance by changing the specific surface, porous structure and the type, content and bonding mode of heteroatoms on the surface of activated carbon [6,7]. In this paper, distilled water was used in DBD plasma as a pollution-free medium to enhance the electrochemical properties of CSAC. It is suitable for practical application in that DBD plasma modification can dramatically reduce the processing time and does not require vacuum equipment
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