Biofuel Cells. Группа авторов
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Название: Biofuel Cells
Автор: Группа авторов
Издательство: John Wiley & Sons Limited
Жанр: Физика
isbn: 9781119725053
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1.4 Supports for Immobilization of Enzymes and Microorganisms for Biofuel Cells
The development of biofuel cells, BFCs (enzymatic fuel cells and microbial fuel cells) are of great interest as was mentioned above. The main limitations of these devices are their short lifetimes and low-power density associated with different losses (Figure 1.7). These limitations are related to the issues raised during immobilization of biocatalysts on electrodes to enable a direct electron transfer. At present, many reported BFCs employ redox mediators as electron shuttles involving the addition of an extra interface between the fuel and the solid electrode. Moreover, mediators are typically expensive, unstable and potentially toxic [85].
Therefore, one of the efforts to increase the life-time and power density is related to the development of nanomaterials, which facilities the electron transfer between the enzymes/microbes and the electrode [86–89]. For this purpose, the morphological and electronic characteristics of nanomaterials must decrease the different losses displayed in Figure 1.7a. At the same time, the nature of the nanomaterial must be smartly selected since biocompatibility and toxicity are highly important in microbial fuel cells; antibacterial materials can cause losses of activity and durability. According to the science of materials, the modifications that can be done to a support can be classified as morphological or electronic (Figure 1.8). The most commonly reported supports for BFCs are carbon allotropes because they are nontoxic, abundant, cheap, and easy to prepare and to reproduce [90–92]. The effect of nanomaterials on the performance of BFCs is directly related to the changes in the affinity between the biocatalyst and the nanomaterial from a point of view of adsorption and chemical integration [85]. The increase in surface area boosts the contact points of the biocatalyst, improving the electron flow from the fuel to the electrode and the diffusion of mediators in the electrodes. There are several reviews dealing with the use of nanomaterials in BFCs [6–14, 90–98]; however, in the following pages the use of supports will be covered from a materials science point of view dealing with the latest findings (2017–to date).
Figure 1.7 (a) Schematic representation of a polarization curve for an ideal and a real BFC, and (b) representation of current density and potential losses during time.
In general, the classification of the reported nanomaterials for BFCs is presented in Figure 1.9; being carbon allotropes the most reported materials. Carbon materials that are of high interest in BFCs in recent years are buckypaper, carbon paper and nitrogen-doped graphene. Therefore, the discussion will be centered on them.
Figure 1.8 Structural and electronic modifications of supports to improve the electrocatalytic properties in biofuel cells.
Figure 1.9 Types of supports reported for biofuel cells.
1.4.1 Buckypaper Bioelectrodes for BFCs
Buckypapers are thin sheets composed of entangled carbon nanotubes, where the thickness can be modulated from tens of nanometers to hundreds of micrometers [99]. Walgama et al. prepared buckypaper with different thickness, finding that 87 μm was the minimal thickness required to develop a mechanically stable electrode to be in contact with aqueous solutions for BFCs [100]. The group of Serge Cosnier has published interesting works related to the use of buckypaper bioelectrodes functionalized with several mediators for glucose biofuel cells. In a recent work, their group used 1,10-phenanthroline-5,6-dione (PLQ) as mediator in a glucose biofuel cell achieving open circuit voltages (OCVs) between 0.67 and 0.74 V, and power densities up to 24 mW cm−3 in a single compartment BFC [101]. Additionally, the same group reported the use of buckypaper functionalized with a pyrene–polynorbornene homopolymer for a flexible lactate BFC [102]. This BFC delivered an OCV of 0.74 V, and a maximum power density of 520 μW cm−2. Güven et al. used buckypaper as bioelectrodes for pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase/laccase glucose BFC [103]. The function of buckypaper was to diminish the electrochemical barriers for a direct communication of these enzymes. Thus, a maximum OCV of 0.44 V was achieved, while 49.16 μW cm−2 was the highest achieved power density. Bollella et al. reported a miniaturized glucose BFC based on buckypaper electrodes using PQQ-dependent glucose dehydrogenase and bilirubin oxidase. This BFC achieved an OCV of 0.6 V and a maximum power density close to 10 μW. In addition, the authors implanted the BFC in a living slug obtaining an OCV of 0.31 V, and a power density of 2.4 μW (~4-fold lower to that obtained in ideal conditions) [104]. Hou and Liu reported the use of buckypaper for the incorporation of flavin adenine dinucleotide-glucose dehydrogenase and laccase in a glucose BFC coupled to a supercapacitor based on carbon nanotubes and polyaniline [105]. This combined device achieved 0.8 V and a maximum power density of 608 μW cm−2.
1.4.2 Carbon Paper Bioelectrodes for BFCs
Torrinha et al. used a typical methodology reported for buckypaper to prepare paper-like electrodes using Vulcan carbon black, reduced graphene (rG) electrode and carbon nanotubes (buckypaper electrode) [106]. Glucose oxidase and bilirubin oxidase were deposited onto these electrodes, and a finger-powered glucose biofuel cell was constructed. This cell has the advantage of avoiding the use of external СКАЧАТЬ