Cu2+-doped NiCo2O4 composite modified carbon felt cathode in marine sediment microbial fuel cells and its enhanced dissolved oxygen reduction reaction kinetics for higher power output

• Novel Cu 2+ -doped NiCo 2 O 4 /CF cathodes were prepared and employed for the first time in MSMFCs. • The optimized CNCO-0.2/CF-based MSMFC reached a power density of 1043.8 mW·m −2 , stable for 45 days; DORR: E₁/₂ = −0.22 V, J ₀ = 4.85 mA·cm −2 , n ≈ 3.7. • Mechanism studies revealed that Cu 2+ doping introduced O vacancies, oxidized Ni 2+ /Co 2+ to Ni 3+ /Co 3+ , formed nanoneedles, boosting DORR kinetics. • This Cu 2+ strategy guides spinel modification, applies to marine devices, and enriches spinel catalyst theory. The development of efficient and stable non-precious metal cathodes is critical to the practical application of marine sediment microbial fuel cells (MSMFCs). Herein, a series of Cu 2+ -doped NiCo 2 O 4 spinel cathodes were synthesized in-situ on carbon felt (CF) via a hydrothermal growth to enhance the dissolved oxygen reduction reaction (DORR) in seawater. The optimal electrode (CNCO-0.2/CF) exhibited a significantly improved specific capacitance of 180.6 F·m − 2 and a low charge-transfer resistance of 5.6 Ω. When applied in an MSMFC, the CNCO-0.2/CF cathode delivered a high power density of 1043.8 mW·m −2 , which was 5.1 times that of the undoped benchmark (NCO/CF), while maintaining stable operation for 45 days. Electrochemical characterizations verified its excellent DORR activity, as demonstrated by a favorable electron transfer number ( n ≈ 3.7). The enhanced performance is attributed to the synergistic effects of Cu²⁺ doping, which introduced oxygen vacancies, improved electrical conductivity, and formed a unique nanoneedle array structure. This work offers a promising strategy for designing high-performance, cost-effective cathodes for long-term marine energy conversion.