Biomass derived Activated Carbon as Electrode Materials for Electrochemical Double layer Capacitors (EDLC)

The development of biomass-derived activated carbon as electrode materials for electrical double-layer capacitors (EDLCs) are receiving much attention because of the environmental impacts and economic value. Most of the published work are using chemically activated carbon, there is not much research on the development of biomass-derived activated carbon (AC) using physically activated carbon for supercapacitors applications. In the present work, AC derived from five selected waste biomass were prepared using a two-step CO2-activation method. Symmetrical two-electrode coin cell using AC derived wastes biomass as electrode material was assembled to study the electrochemical performance in the organic electrolyte, 1 M TEABF4 in PC. The chemical composition and the porous structure of Marabú derived AC are greatly influenced by the carbonization heating rate and the activation holding time. M10V8 exhibits the highest surface area of 1977m2g-1 and delivers ~20F/g at 1Ag-1 with good cyclability. The performance of Marabú derived AC was investigated in ionic liquid [EMIM][BF4]. Specific capacitance up to 32Fg-1 at 1Ag-1 was achieved using M10V8 in the ionic liquid system. However, great energy degradation was observed. Next, the effect of CO2 activation temperatures (9500C and 10000C) was studied using spent coffee ground (CG) as the carbon precursor. CG as carbon material which treated with activation temperature of 1000oC and up to 100mins (C10W10) exhibited the highest specific capacitance (22Fg-1) and energy density of ~15Whkg-1 when operating at 400Wkg-1 in 1 M TEABF4 in PC. AC with the activation temperature of 9500C only provides specific capacitance of less than 3Fg-1. This elucidated that the AC properties are strongly dependent on CO2 activation temperature applied. High burn-off and high thermal sensitivity have limited the possibility of rubberwood (RW) in EDLC applications. Although same activation condition was applied to produce ACs from Malaysia wood pellets (MS) and oil palm empty fruit bunch pellets (EFB), porosities and surface area of ACs highly depends on the selection of biomass as the activated carbon precursors. An ideal EDLC CV curve without any Faradaic reaction was observed although high ash content is observed in both biomass-derived ACs. The impurities, however, accelerated the cell aging problem with great energy loss. Overall, this research has proven the great potential of CO2 activation to prepare high surface area AC from biomass for EDLC applications.