Preparation Of Biomass And Organic Salt-based Activated Carbon And Their Electrochemical Performances

Activated carbon has shown excellent performance in many fields,and the demand of its commercial applications promote the selection of raw materials to pursue a more simple and inexpensive technology.However,the physical structures of activated carbon is closely related to the treatment processes.Therefore,this paper was starting from the selection of carbon sources and activation technologies,the activated carbon with high specific surface area was obtained by a simple preparation process.The correlation between their physical structures and electrochemical properties were analyzed,and the active centers of activated carbon were clarified to provide a basic research for the industrial applications.Biomass cotton stalks and poplar chips were selected as carbon sources,respectively.Nitrogen doped porous carbon was obtained from cotton stalks by CO₂ and KOH activation.The analysis showed that KOH activation had a strong ability to develop pore structures,specific surface area and total volume of chemical activitated carbon（c AC）were about three times higher than CO₂ activation sample physical activitated carbon（p AC）.However,the N doping with the content of 3.53 at.%came from p AC,which was higher than c AC（2.15 at.%）.In addition,the effects of wet and dry KOH activation processes on the pore structures of activated carbon were evaluated.The analysis showed that the specific surface area of the wet activated carbon（w AC）and dry activated carbon（d AC）of KOH activation samples were1938 m² g^-1 and 1429 m² g^-1,respectively.But the nitrogen content was similar.The capacitance of w AC reached to 289 F g^-1,which was higher than c AC(232 F g^-1)at 1 A g^-1in supercapacitor.The higher energy density of w AC was 26.6 Wh kg^-1.In hydrogen evolution reaction,p AC possessed an overpotential of 421 m V,due to its pyridine-N content of 0.54 at.%.In oxygen evolution reaction,the c AC displayed an overpotential of 230 m V,which was lower than p AC（366 m V）,d AC（287 m V）and w AC（329 m V）,the high specific surface area and the functional group of C=O together contribute to the high activity.In oxygen reduction reaction,the average transfer electrons of c AC and w AC were close to 4e,which was related to their high specific surface area,abundant oxygen-and nitrogen-containing functional groups.In Zn-air battery,the open circuit voltage of c AC was 1.41V,its maximum power density was 26.4 m W cm^-2.Besides,c AC showed stability during constant current discharge and cyclic charge and discharge.S,N co-doped hierarchical porous activated carbon was obtained from polystyrene sulfonate organic salts by one step pyrolysis under N₂ atmosphere.The influences of activation temperatures on physical and chemical properties of activated carbon were discussed.The results showed that the pore structures of the S,N co-doped samples were mainly microporous,accompanied by a small number of mesoporous and macroporous.From800 ^oC to 900 ^oC,the total content of sulfur in carbon structures had been reduced from 0.95at.%to 0.67 at.%,and sulfoxide sulfur as the main group was existed in AC-900.However,the nitrogen content continued to increase,0.37 at.%content of pyridine-N was existed in AC-900.AC-900 had a capacitance of 182 F g^-1 at 1 A g^-1 in supercapacitor,and its maximum energy density was 23.4 Wh kg^-1.In hydrogen evolution reaction,the overpotential of AC-900 was 450 m V,and the Tafel slope was 163.3 m V dec^-1,the S,N co-doped activated carbon had significantly improved the kinetic process of HER,comparing with nitrogen doped activated carbon from biomass.