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A hydrogen/oxygen hybrid biofuel cell comprising an electrocatalytically active nanoflower/laccase-based biocathode

Enzymatic fuel cells (EFCs) are one of the promising next-generation energy conversion systems. However, their applications are often obstructed by their power density and their lack of long-term operational stability. Enzyme immobilization is one of the strategies to overcome these limitations. The construction of a surface-confined electrode architecture that provides biocompatible microenvironments for enzyme immobilization might be a promising approach to address such barriers. Inspired by the interaction between laccase and copper ions leading to the growth of micrometer-sized flower-like particles, we successfully demonstrate a cathodic electrode design using these hybrid nanoflowers as a biocatalyst for oxygen reduction. Using this electrode architecture, enhanced activity and stability are achieved. By integrating this cathode in a fuel cell setup, two H2/O2 fuel cell configurations have been constructed: a membraneless fuel cell (MFC) and a proton exchange membrane H2/O2 fuel cell (PEMFC) that show enhancement of the performance. The cell is equipped with an oxygen-reducing laccase–Cu nanoflower/carbon nanotube biocathode and an abiotic anode. The maximum power densities of the H2/O2 MFC and PEMFC were 52 μW cm−2 and 0.41 mW cm−2, respectively. Remarkably, the H2/O2 PEMFC system maintained ∼85% of its initial power density for 15 days at room temperature, which was greatly improved when compared with previous fuel cells with different nanostructures. These results allow a great variety of conductive biocompatible cathodes to be used and engineered, opening vast possibilities for the development of bioelectronics and biosensors.