Novel nano biomass (NBM) was synthesized using a general and simple synthetic approach. In this process, the walnut shell is used as a green carbon source. According to the transmission electron microscopy and dynamic light scattering results, the average particle size of the produced activated carbon was 2.25 nm. The surface area of the NBM was around 420.5 m(2)/g totally. High pore volume, high internal surface area, lightweight as well as easy availability are some features that attract research interests on activated carbon as a solid-state hydrogen storage medium. Nano biomass was deposited directly on a copper substrate by the slurry-coating method. The electrochemical properties of nano biomass were investigated in a three-electrode electrolytic cell with 6 M KOH as the electrolyte by galvanostatic charging and discharging. Several parameters such as the impact of the number of charge and discharge cycles and discharge time are studied. Different experimental results show that Cu-NBM has 1596 mAh/g discharge capacity (corresponding to a hydrogen storage capacity of 5.66 wt%) after 16 cycles at room temperature and atmospheric conditions. Due to porosity of NBM particles, the nano biomass showed reversible hydrogen storage capacities that were better than those of previously reported porous carbons. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.