![]() The resulting nanostructured electrodes can enable increased surface area and enzyme loading, provide a favourable confined environment for long-lasting immobilization of enzymes, and facilitate high-efficiency electron transfer while circumventing the need for mediators. It is also clear that the current trend of developing high-performance micro EBFCs is highly related to recent progress in nanoscience and nanotechnology. In 2001, the first revolutionary micro EBFC utilizing a single carbon fibre as the microelectrode and body fluids as biofuel was demonstrated by Heller 15, which revealed the feasibility of using EBFCs to power miniaturized IMDs. In the past two decades, few efforts have been made to improve the power density, lifetime, immobilization methods, enzyme loadings, and cell designs 12, 13, 14. 11 made one of the most outstanding contributions by discovering direct electron transfer (DET) in 1978. Since then, research on EBFCs remained relatively unnoticed until Berezin et al. The early work on EBFCs in the 1960s involved the use of a purified enzyme and a mediator for performing mediated electron transfer (MET) to the electrode surface 9, 10. ![]() 1, i.e., Galvani’s bioelectricity in 1791 4, water electrolysis in 1839 5, the initial half-cell using Escherichia coli in 1910 6, the first microbial biofuel cells in 1931 (later funded by the NASA space program) 7 and the first EBFC using cell-free enzyme in 1964 8. Major milestones in the evolution of bioelectricity generation are illustrated in Fig. EBFCs offer competitive advantages over conventional power sources, including the utilization of renewable and nontoxic biocomponents, high reaction selectivity and activity of biocatalysts, abundance of biofuels, and physiological operating conditions (human body temperature and near neutral pH) 3. On the cathode, a laccase catalyst reduces molecular oxygen and generates water by combining the oxygen atoms with electrons and protons. In principle, glucose is catalysed by glucose oxidase (GOx), produces gluconolactone and protons, and generates electrons on the anode. Enzymatic biofuel cells (EBFCs), a subclass of fuel cells that employ enzymes to convert biological energy into electricity, have been touted as a potential power source for IMDs with typical power requirements of micro- to milliwatts 2. Due to economic and ecological concerns, alternative green and efficient power sources should be sought to replace current commercially available lithium-ion batteries. Similar content being viewed by othersĭriven by demographic factors such as shifting lifestyle choices, degenerative chronic diseases, and growing geriatric population, the market for implantable medical devices (IMDs) stood at $43.1 billion in 2011 and is expected to increase to $116.3 billion by the end of 2022 1. The experimental power density is noted to be 71.1% of the theoretical value. The experimental results from the developed rGO/CNT-based EBFC showed a maximum power density of 196.04 µW cm −2 at 0.61 V, which is approximately twice the maximum power density obtained from the rGO-based EBFC. Theoretical modelling of the rGO/CNT-based EBFC system via finite element analysis was conducted to predict the cell performance and efficiency. The Michaelis–Menten constant K M of 2.1 mM for glucose oxidase (GOx) on the rGO/CNTs/GOx bioanode was obtained, which is close to the K M for free GOx. The fabrication process of this system combines the top–down carbon microelectromechanical systems (C-MEMS) technique to fabricate the 3D micropillar array platform and bottom–up electrophoretic deposition (EPD) to deposit the reduced rGO/CNTs/enzyme onto the electrode surface. Here, we report a closed-loop theoretical and experimental study on a micro EBFC system based on three-dimensional (3D) carbon micropillar arrays coated with reduced graphene oxide (rGO), carbon nanotubes (CNTs), and a biocatalyst composite. Miniaturized enzymatic biofuel cells (EBFCs) with high cell performance are promising candidates for powering next-generation implantable medical devices.
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