Abstract
Carbon electrode materials for double layer capacitors have attracted much attention, due to their low cost and abundant sources. Their low specific capacitance, however, hinders the development of carbon electrode materials. In this paper, the large specific surface area commercial activated carbons, rich in micropores, were initially oxygen-functionalized by treatment using concentrated H2SO4, saturated (NH4)2S2O8, and H2SO4/(NH4)2S2O4 mixed oxidants, respectively. The as-prepared samples were analyzed using N2 adsorption/desorption isotherms, X-ray photoelectron spectroscopy, and Boehm titration, and used as electrode materials for supercapacitors. Characterization results displayed that the oxidation treatment decreased the specific surface area along with increasing oxygen content. The electrode test showed that the electrochemical activity increased as oxygen content increased. The result that oxygen-functionalized activated carbon, even with a lower specific surface area but much more oxygen content, had higher capacity than pristine activated carbon, tells of the critical role of oxygen functional groups. The excellent capacitive performance suggests a good potential for oxygen functional carbon material to be a highly promising electrode material for supercapacitors.
Highlights
Inexpensive, stable, and much efficient energy storage devices are very crucial for the growing demand for sustainable energy and electric vehicles
We successfully developed an inexpensive, porous, activated carbon material, rich in oxygen-containing groups, and studied the effect of oxygen functional groups upon the capacitive performance; a redox reaction built upon oxygen-functionalized carbon electrode materials was proposed, to explain the much improved capacitive behavior
The specific surface area was obviously reduced from 901.4 m2 /g for activated carbon (AC)-o, to 708.7 m2 /g for AC-s, 490.0 m2 /g for AC-a, and 489.3 m2 /g for AC-m (Table 1)
Summary
Inexpensive, stable, and much efficient energy storage devices are very crucial for the growing demand for sustainable energy and electric vehicles. Supercapacitors (SCs) have been extensively acknowledged as backup power devices, energy conservation, and power tools, and are expanding their applications in electrical vehicles [1,2,3,4]. A broad variety of appropriate electrode composites have been explored, mainly built upon charge accommodation at the electric double layer and the occurrence of Faradaic reactions [5]. These electrode materials are mainly constituted by metal oxides, conductive polymers, and porous carbon materials. Of the extensively studied electrode materials of transition metal oxides, RuO2 displayed the excellent initial electrochemical performance, whereas the cost of precious metal oxides and difficulties in large-scale production limited its practical applications [6,7]. Porous carbon materials have emerged as the most potential alternative, owing to their cheapness, high supply, outstanding conductivity, eco-friendliness, and steady structural characteristics
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