Waste microalgal biomass-derived biochar electrode for sustainable high-performance supercapacitors: Experimental and computational insights

Agricultural and algal biomass residues are emerging as promising low-cost feedstocks for energy storage electrodes. In this work, waste Dunaliella salina microalgal biomass was converted into biochar through pyrolysis and directly deposited onto nickel foam to fabricate a binder-free electrode. The biochar electrode exhibited a high specific capacitance of 507.9 F/g and maintained 104 % retention after 2000 continuous cycles, highlighting excellent electrochemical reversibility in alkaline electrolyte. Complementary density functional theory (DFT) simulations using a nitrogen/oxygen co-doped graphene supercell revealed a strong potassium adsorption energy, partial charge transfer to heteroatom-rich sites, and band structure modifications, including gap opening (0.1861 eV), all indicating enhanced ion affinity and transport. These theoretical findings complement the experimental results, providing a fundamental understanding of the role of heteroatom doping in optimizing electrochemical performance. This work presents a sustainable pathway for developing high-performance electrode materials using microalgal biomass wastes. • Microalgae-derived biochar electrodes were developed for supercapacitors. • The prepared biochar electrode achieved 588.0 F/g specific capacitance at 46.2 A/g. • The material retained 104.0 % of its capacitance after 2000 charge-discharge cycles. • DFT simulations showed enhanced ion affinity and transport for boosted performance.