Beijing Key Laboratory of Lignocellulosic Chemistry Beijing Forestry University Beijing 100083 China;
Center for Lignocellulose Science and Engineering Liaoning Key Laboratory Pulp and Paper Engineering Dalian Polytechnic University Dalian Liaoning Province 116034 China;
lignin; phosphoric acid-assisted pretreatment; two-step activation; hierarchical porous carbon; supercapacitors; electrochemical performance;