Nature-powered bio-cathodes: Synergistic effects of laccase immobilization and green nanoparticles on enhanced PGEs for sustainable biofuel cells

As part of growing energy demands and threats to ecology, there is an immense need for greener energy technologies that are novel, cost-effective, and ecofriendly. This paper presents a scalable strategy that uses biocompatible nanomaterials to modify the surface of a pencil graphite electrode (PGE) to enhance the performance of enzymatic biofuel cells (EBFC). Rosa centifolia flowers, an abundantly available plant extract, was used to green synthesize Ag and Cu nanoparticles and applied to various grades of pencil graphite lead surfaces (2H, HB, 2B) via dip-coating, and covalently immobilized with laccase enzyme. Unlike conventional nanoparticles, green-synthesized nanoparticles retain functional groups from phytochemicals that facilitate stable enzyme immobilization, resulting in effective electron transfer. Among the tested biocathodes 2B grade Lac/AgNP/PGE and Lac/CuNP/PGE demonstrated the highest open circuit potentials of 0.611 V and 0.498 V and current densities 1343.15 μA cm⁻² and 1054.17 μA cm⁻² respectively resulting in a significant raise of 70.84 % over pristine PGEs. Polarization studies revealed superior power density for Lac/AgNP/PGE-2B (20.629 μW cm⁻² at 65.21 μA cm⁻² current density) over Lac/CuNP/PGE-2B (17.39 μW cm⁻² at 61.9 μA cm⁻² current density). SEM confirmed enzyme immobilization, and FTIR and XPS validated the presence of carboxyl functional groups. Considering the stability of the modified electrode, Lac/AgNP/PGE-2B retained 62.93 % of its original current density on Day 20. This approach delivered a performance-enhanced biocathode design using functional nanomaterials and a bio-supportive strategy that displayed remarkable stability, longevity, and efficiency, and could potentially optimize the cost of EBFC design and promote miniaturization.