活性炭表面改性对双电层电容器电化学性能的影响

通过氢气还原改性和浓硝酸氧化处理对石油焦基活性炭(ACs)进行改性.采用氮气吸附和脱附等温线计算改性ACs的BET比表面积、 DFT孔径分布及孔容,以XPS方法表征改性ACs的表面含氧官能团种类及含量,改性ACs的电化学性能通过直流循环充放电、循环伏安等表征.结果表明:浓硝酸处理后,ACs比表面积和孔容均稍有减少,表面含氧官能团和比电容明显增加,内阻和自放电显著增大;氢气改性后,ACs比表面积和孔容亦稍有减少,孔径分布的变化使比电容明显增加,氧化官能团的减少降低了内阻并减少了自放电.即,氢气改性ACs的电化学性能明显提高,增加了比电容,降低了内阻和自放电.

Effect of the surface chemistry of activated carbon on its electrochemical properties in electric double layer capacitors

Petroleum coke-based activated carbons(ACs)were modified through H2 reduction and HNO3 oxidation. Pore structures and surface chemistry of the ACs were characterized by N2 adsorption and X-ray photoelectron spectroscopy. The Brunauer-Emmett-Teller surface areas of ACs were slightly decreased after such treatment. Although surface oxygen groups(especially carbonyl groups)were generated when ACs were treated by HNO3, electric double layer capacitance, internal resistance(IR), equivalent series resistance(ESR), and self-discharge of an AC electrode exhibited a remarkable increase. At the same time, the number of surface oxygen groups of ACs modified by H2 remarkably decreased and the capacitance was markedly increased , while IR, ESR, and self-discharge decreased. This reduction modification of ACs is beneficial in improving electrochemical properties and probably provides suitable pores for electrolyte to penetrate electrochemically.