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The global energy demand has been rising sharply with the rapid growth of the population. Traditional fossil fuels are gradually being depleted due to massive consumption, and their combustion emissions have exacerbated environmental problems such as global warming. Against this backdrop, fuel cells, as a sustainable energy solution, have received extensive attention. Enzymatic biofuel cells (EBFCs), which can operate at human body temperature and physiological pH, show unique application potential in the biomedical field and can be used to manufacture devices such as pacemakers and cochlear implants. However, the development of EBFCs faces some challenges, such as the immobilization of redox enzymes on the electrode surface and the efficiency of electron transfer. The traditional mediated electron transfer (MET) technology has defects such as a decrease in mediator sensitivity and vulnerability to poisoning. Therefore, it is crucial to develop efficient and stable anode materials for enzymatic biofuel cells. This study aims to address the above issues and improve the performance of EBFCs by preparing electrospun mediator-less polyaniline-based enzymatic biofuel cell anodes with the help of an electrospinning machine.
In this study, composite fibers of polyaniline (PANI) and polystyrene were prepared by electrospinning device, deposited on a glassy carbon electrode (GCE), and then glucose oxidase (GOx) was immobilized to successfully fabricate a bioanode (Figure 1). This preparation method effectively improves the enzyme immobilization efficiency and lays a foundation for achieving efficient electron transfer.
Thermal Stability Analysis: The thermal stability of the composite fibers was studied by thermogravimetric analysis (TGA). The results show that the composite fibers exhibit different degrees of weight loss in different temperature ranges, indicating good thermal stability, which is superior to pure PANI. This provides a guarantee for the stability of the bioanode in practical applications (Figure 2).
Functional Group Analysis: The functional groups of the composite fibers were analyzed using Fourier transform infrared spectroscopy (FTIR). The characteristic absorption peaks in the spectrum confirm the presence of various functional groups in the composite material, providing important evidence for understanding the chemical structure and properties of the material (Figure 3).
Crystallinity Analysis: X-ray diffraction (XRD) analysis shows that the prepared bio-composite material is crystalline. The sharp peaks at specific 2θ values prove the crystallization behavior of the electrospun nanofibers, which helps to improve the electrical properties of the material (Figure 4).
Morphology Observation: The morphology of the composite fibers was observed by scanning electron microscopy (SEM) and high-resolution scanning electron microscopy (HR-SEM). The results show that the composite fibers form a dense, randomly entangled spider-web structure with a smooth and bead-free surface, and PANI is evenly dispersed inside the polystyrene fibers. This structure is conducive to enzyme immobilization and electron transfer (Figure 5).
Cyclic Voltammetry (CV): The PANI-polystyrene/GOx composite fibers were studied by CV. The results show that this composite biomaterial provides effective electrical communication between the enzyme active site and the electrode surface without the need for an additional mediator. With the addition of GOx, the current density and redox peaks increase significantly, and within a certain range, the current density has a linear relationship with the scan rate, indicating that the electrode process is diffusion-controlled.
Electrochemical Behavior in the Presence of Glucose: In the presence of glucose, the current density of the PANI-polystyrene/GOx anode increases significantly. At a glucose concentration of 20 mM, the anode generates a maximum current density of 2.689 mA/cm², indicating that the anode can effectively catalyze the oxidation of glucose to generate current. Moreover, the oxidation potential decreases in the presence of glucose, further proving the promoting effect of the GOx-modified anode on glucose oxidation (Figure 6).
Linear Sweep Voltammetry (LSV): The LSV results show that as the glucose concentration increases, the catalytic current generated by the bioanode increases linearly in the range of 0 - 20 mM. After reaching the maximum value, continuing to increase the glucose concentration leads to a gradual decrease in the current density, which is due to the saturation phenomenon caused by excessive glucose concentration (Figure 7).
Electrochemical Impedance Spectroscopy (EIS): EIS studies show that there are semicircular and linear regions in the Nyquist plot, corresponding to the charge transfer limiting process and the diffusion-controlled reaction, respectively. A smaller semicircle diameter indicates good electron transfer ability of the PANI-polystyrene composite, while an increase in the semicircle diameter after enzyme modification proves the successful immobilization of the enzyme on the bioanode.
This study successfully prepared a fibrous bioanode for enzymatic biofuel cells. The anode exhibits excellent electrical response in the presence of 20 mM glucose, generating a current of 2.689 mA/cm², which is close to the glucose concentration in human blood. At the same time, the bioanode has significant operational stability, with no obvious change in current density within 15 days, followed by a slow decline. The electrospinning process increases the porosity and surface area of the fibers, helping to expose more enzyme active sites and achieve better enzyme immobilization. This study provides a feasible solution for reducing the dependence of enzymatic biofuel cells on traditional mediators and lays a foundation for the development of miniaturized and wearable enzymatic biofuel cells. Future research can further explore the addition of nanoparticles, carbon nanotubes, and other materials to improve the power output of bioanodes and promote the practical application of enzymatic biofuel cells.
Article source: https://doi.org/10.1016/j.matchemphys.2025.130814
