Structurally engineered Co-CeO₂ dispersed on N-lemon biochar for efficient energy storage and water splitting

Herein, we report Co-doped CeO₂ anchored on N-doped lemon-peel biochar (Co-CeO₂/N-LB) as a multifunctional platform for simultaneous energy conversion and storage. The synergistic interaction between Ce³⁺/Ce⁴⁺ and Co²⁺ redox centers, abundant oxygen vacancies, and stable M-O-N covalency significantly enhances charge transfer, hydrophilicity, and structural stability. Consequently, the catalyst exhibits lower overpotentials of 289 mV (OER) and 64.51 mV (HER), smaller Tafel slopes, and high TOF (0.552 and 3.97 s^-1). Mechanistically, Ce-O-Co chains stabilize Co-3d electronic states, enabling parallel *H adsorption during HER and spin-assisted oxygen intermediate coupling during OER. Beyond electrocatalysis, Co-CeO₂/N-LB delivers rapid energy-storage performance, achieving higher specific capacitance (1664.16 F g^-1), energy density (36.98 Wh kg^-1) and (0.166 kW kg^-1) power density. Charge storage kinetics are governed by a near-equal diffusive (49%) and capacitive (51%) contribution, ensuring fast response and excellent durability over 9500 cycles. Furthermore, when supported on carbon paper, Co-CeO₂/N-LB demonstrates lower overpotentials (359.63 and 244.43 mV) and stable performance over 10 000 cycles along-with high specific capacitance (1650 F g^-1), while post-stability analyses verify retention of the Co-CeO₂ and N-LB planes in Co-CeO₂/N-LB, highlighting its promise as a dual-functional electrode for integrated electrocatalysis and rapid energy storage.