A simple one-step preparation of biomass derived carbon materials with hierarchical pore structure for supercapacitor application is proposed. Briefly, potassium citrate is loaded onto poplar catkin, a forestry and agricultural residue, for carbonization at different temperature (750-900 degrees C). With the confined effect of poplar catkin and pore-forming role of potassium compounds, interconnected carbon networks combining of macropores, small mesopores and micropores are obtained. The product carbonized at 850 degrees C (S-850) processes large surface area of 2186 m(2)/g with two main micropore ranges distributed in 0.5-0.7 nm and 0.7-1.5 nm, and the sample of S-900 processes relatively high electrical conductivity because of the high degree of graphitization. The electrodes based on these carbon materials show main electrical double-layer capacitors with small part of pseudo-capacitors due to O-doping. The S-850 sample displays superior specific capacity at low charge-discharge current density while the electrode based on S-900 shows high specific capacity under high current density. The symmetrical devices based on S-850 give a superb stability and high energy and power densities in alkaline electrolyte. Within a voltage window of 1.4 V, the device can deliver a 13.3 Wh/kg energy density at a power density of 720 W/kg and maintain 7.8 Wh/kg at 14040 W/kg. (C) 2020 Elsevier Inc. All rights reserved.