Rapid Preparation Of Enzymatic Hydrolysis Lignin-Based Activated Carbon By One-Step Microwave Method

Supercapacitor is widely used in various fields as energy storage device.Activated carbon is the most successful carbon electrode material for supercapacitor in actual production because of its good resistances to chemical corrosion,low price and wide source.Nowadays,the main method to make activated carbon from biomass materials is carbonization followed by activation with traditional contact heating.The whole process lasts long time,energy consumption,low efficiency,greatly prolong the production cycle.In this study,the microwave absorber and activator ZnCl₂ was introduced into the preparation of lignin-based activated carbon from enzymatic hydrolysis lignin（EHL）by one-step microwave preparation.In order to improve the properties of the obtained activated carbon,KOH with a better activation effect was introduced in preparation.Humidified nitrogen was introduced to optimize the reaction device to realize one-step microwave preparation.Also,the preparation of lignin-based activated carbon was further studied by introducing carbon-based microwave absorber materials assisted one-step microwave preparation to simplify the reaction device.Finally,to further improve the performance of lignin-based activated carbon prepared by microwave one-step method,Cu-doped composites activated carbon was prepared by activation of CuCl₂.The results are as follow:（1）The activator ZnCl₂ has the property of absorbing microwave,which can realize the one-step microwave to convert the EHL from biomass to lignin-based activated carbon.The short preparation time of 10 min greatly improves the efficiency.When the reaction time is 10 min and the ratio of EHL and ZnCl₂ is 1:3,the prepared lignin-based activated carbon has a specific area of 842 m²/g,which can be ascribed to the poor activation effect.The final activated carbon-based supercapacitance delivers an energy density of 3.3 Wh/kg and a power density of 1711.8 W/kg.（2）KOH was used to improve the properties of the obtained activated carbon.The humidified nitrogen was introduced to assist one-step microwave preparation because KOH and EHL both absorbs very little microwave energy.KOH could improve the pore structure after activation when compared with ZnCl₂.When the reaction time is 8 min and the ratio of EHL and KOH is 1:3,the prepared lignin-based activated carbon has a specific area of 2482 m²/g and total pore volume of 1.45 cm³/g.The electrode exhibits the specific capacitance of 338.0 F/g（1 A/g）.The final activated carbon-based supercapacitance delivers an energy density of 8.6 Wh/kg and a power density of 2249.0 W/kg.（3）To simplify the experiment device and achieve the one-step microwave preparation with KOH as activator,the carbon-based microwave absorber was introduced to assist the directly conversion from EHL to activated carbon.The preparation is environmentally friendly without the remove of microwave absorber.The obtained activated carbon has a specific area of 2885.5m²/g and total pore volume of 1.47 cm³/g with the 5%additive amount of carbon-based microwave absorber.The specific capacitance of electrode is 326.0 F/g（1 A/g）.The final activated carbon-based supercapacitance delivers an energy density of 7.6 Wh/kg and a power density of 1913.0 W/kg.（4）To further improve the performance of activated carbon as supercapacitors,microwave one-step method using the activator CuCl₂ converted EHL into Cu-doped composites activated carbon.The process sacrifices pore structure development but enhance the electrochemical properties.And the final product does not need pickling.The electrode could exhibits the specific capacitance of 696.0 F/g（1 A/g）.The final activated carbon-based supercapacitance delivers an energy density of 53.7 Wh/kg and a power density of 8050.5 W/kg.