A 1.6 mW cm−2 lactate/O2 enzymatic biofuel cell: enhanced power generation and energy harvesting from human sweat by 3D interpenetrating network porous structure CNT-membranes†

Abstract

Wearable biofuel cells (BFCs) that rely on human sweat for energy harvesting and power generation require highly active enzymes to modify the electrode for biofuel catalysis and oxidation. However, the aggregation and shedding of biological enzymes lead to the coverage and attrition of catalytic active sites, making it difficult for currently reported BFCs to exceed a power density of 1 mW cm⁻². An electrode that increases the biological enzyme load space and enhances the active site area is yet to be developed. Herein, we present CNT membranes with a 3D interpenetrating, hierarchical, porous structure enabled by non-solvent-induced phase separation for CNT bioanodes in lactate/O₂ BFCs. This interpenetrated porous structure facilitated fast mass-transfer kinetics of biofuels and electrolytes, ultralow electron conduction resistance, uniform and steady accommodation of biological enzymes, and exceptional flexibility that could withstand harsh mechanical deformation. Thus, the CNT bioanode exhibited an impressive power density of 1.6 mW cm⁻² when integrated into a BFC with an air cathode in artificial sweat with only 20 mM lactate. As a human sweat-energy-harvesting device, 1 cm² of the CNT bioanode could continuously operate for 36.8 h and harvested 4953.6 mJ of energy. Moreover, the device was capable of powering a high-power Bluetooth and sensor integrated circuit while being compatible with a customized smartphone app for real-time monitoring of human electrocardiograms. The strategy of designing a CNT membrane with a 3D interpenetrating network, porous structure has great potential for the development of future high-performance self-sustainable electronic device systems.