Biofuel Cells. Группа авторов

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СКАЧАТЬ finger force for that purpose. The authors found that paper-like electrode of rG outperformed buckypaper and Vulcan carbon black paper-like electrodes. Escalona-Villalpando et al. evaluated the use of nanofoam-like carbon paper in hybrids bioanode/cathode & anode/biocathode glucose nanofluidic BFCs and in a full glucose nanofluidic BFC [107]. The authors found that the OCV in the glucose oxidase & Pt/C hybrid BFC was 0.55 V, and it can be increased to 0.91 V using a AuAg anode with a laccase biocathode. In addition, the full BFC achieved 0.44 V and a maximum power density of 3.2 mW cm⁻². Escalona-Villalpando et al. also reported the effect of stacked microfluidic biofuel cells on the power density. For this purpose, they worked with glucose dehydrogenase as anodic biocatalyst and bilirubin oxidase as cathodic biocatalyst [108]. A single cell BFC enabled 0.78 V and 0.36 mW cm⁻², while four cells stacked in parallel achieved 0.53 mW cm⁻², and these cells stacked in series enabled an OCV of 1.27 V and a power density of 0.38 mW cm⁻². However, the most effective way that they found to improve the cell performance was stacking four cells 1 and 2 in series and 3 and 4 in parallel, achieving an OCV of 1.23 and a power density of 0.42 mW cm⁻².

Another kind of carbon paper electrodes consisted in carbon fiber arrays; Koushanpour et al. developed an all glucose biofuel cell using this electrode and the H₂O₂ generated in the anode as oxidant [109]. They reported that the use of Meldola’s blue as catalyst for the electro-oxidation of NADH and hemin as catalyst for H₂O₂ reduction resulted in OCVs close to 0.5 V.

      1.4.3 Nitrogen-Doped Carbonaceous Materials as Bioelectrodes for BFCs

      The doping of carbon-based materials with heteroatoms (N, B, P, and S) is a route to activate the π electrons through creation of charge sites, being these responsible of an enhanced conductivity and activity toward the oxygen reduction reaction (ORR). Highly conductive supports like graphene have been modified with heteroatoms for their use as cathodes in hybrid biofuel cells. Du et al. grew N-doped carbon nanotubes on reduced graphene oxide (rGO) nanosheets to improve the performance of a microbial fuel cell (MFC) [110]. The maximum power density achieved by this biofuel cell was 1,329 mW cm⁻², which was 1.37 times higher to that achieved by benchmarked Pt/C, and the improvement was associated to the strong covalent bonds formed between the carbon nanotubes and graphene facilitating the electron transfer between these interfaces. Zhong et al. followed a similar strategy developing a N-doped hierarchical carbon [111]. This material also contained Fe species in its structure, and was obtained through the carbonization of metal–organic frameworks (MOFs). This material was used as cathode in a microbial fuel cell using carbon felt and carbon cloth as anode and cathode, respectively, and the highest performance reported was 1,607.2 mW cm⁻³.

N-doped materials have been used in the anode compartment of microbial fuel cells. Guan et al. [112] synthesized N-doped carbon dots on carbon paper electrodes to improve microbial immobilization. One of the first findings was that the biofilm has 2 times higher thickness in this electrode in contrast with an unmodified carbon paper electrode. In addition, the cell performance was boosted because the extracellular electron transfer process from the microorganisms to the electrode was improved. Zhang et al. [113] used a N-doped graphene as support for a Mo₂C nanocatalyst to improve the hydrogen evolution reaction in a microbial fuel cell stacked with an ammonia electrolytic cell. The authors reported a maximum power density of 536 mW cm⁻², achieved using four air-cathode MFCs stacked in series. Guo et al. [114] also improved the anode of a MFC synthesizing a N-doped 3D expanded graphite foam, which displayed a maximum power density of 739 mW cm⁻², 17.4 times higher than the performance obtained by a simple graphite foil. The activity improvement was attributed to a higher surface area which allowed a bigger growth of the biofilm.

      N-doped carbonaceous materials have been also used in enzymatic biofuel cells. Li et al. [115] reported a covalently coupled ultrahigh quaternary N-doped reduced graphene/carbon nanotube as support for glucose/O₂ enzymatic BFCs. The improvement between electron-accepting pyridinic-N and electron-donating quaternary-N resulted in an ultrahighdonating quaternary N-doping material, improving the electron transfer and thus, the BFC displayed an OCV of 0.89 V with a maximum power density of 0.9 mW cm⁻².

      1.4.4 Metal–Organic Framework (MOF)-Based Carbonaceous Materials as Bioelectrodes for BFCs

MOFs have advantages over typical carbon supports such as tailorable properties from the preparation method, large specific surface area (SSA), high porosity and easy modification with metal atoms and heteroatoms like nitrogen [116]. Porous carbon supports obtained through calcination of MOFs have attracted attention in the energy conversion area because the high specific surface area and ordered porous structure enable a convenient path for electron transfer [117]. In MFCs, these materials are highly used to improve the oxygen reduction, and there are several works focused on this topic as was highlighted in a recent review [118]. Wang et al. [117] obtained a hollow material based on Cu/Co/N with a BET surface area of 286 m² g⁻¹ and a half-wave potential shifted to more positive values in contrast with a benchmarked Pt/C electrocatalyst. This improvement was attributed to the electron properties of this MOF-derived material, which displayed an OCV of 0.68 V, and a maximum power density of 1,008 mW cm⁻². This performance is comparable to that obtained with N-doped materials [110–114]. Zhong et al. [119] obtained a MOF-derived electrocatalyst for oxygen reduction reaction in MFCs using Zr-based MOF UiO66-NH₂ and incorporating Co–Nx active components. This electrocatalyst had a BET surface area of 279 m² g⁻¹ and, similarly to the Cu/Co/N, this material had a more positive half-wave potential (35 mV) than the benchmarked Pt/C. The cell performance evaluation indicated that this material achieved an OCV of 0.39 V and a maximum power density of 299.62 mW cm⁻², which was slightly lower to that obtained by Pt/C (312.59 mW cm⁻²). Wang et al. [120] used the isoreticular metal organic framework-3 (IRMOF-3) modified with g-C₃N₄ nanosheets to obtain a N-doped carbon material with a BET surface area of 686.41 m² g⁻¹. This material displayed superior activity in half-cell and full-cell experiments, the half-wave potential and current density were superior to those obtained for benchmarked Pt/C (0.89 vs. 0.79 V and 6.35 vs. 5.51 mA cm⁻², respectively). Additionally, the maximum power density was 1,402.8 mW cm⁻³, which was 110 mW cm⁻³ higher to that obtained by Pt/C. Xe et al. [121] reported an electrocatalyst for oxygen reduction reaction in MFCs based on zeolitic imidazolate framework (ZIF-8), this new material displayed a BET surface area of 1,416.19 m2 g⁻¹, which is larger to that previously mentioned. Consequently, the maximum power density was 2,103.4 mW cm⁻², which also at least 3 and 3 times higher to that reported in the previous works. The ZIF-8 was then modified with polypyrrole to fabricate a polyhedral porous carbon embedded N-doped carbon networks (PPC/NC) [122]. This material presented a surface area of 342.3 m² g⁻¹, but the improvement in the electron transfer allowed achieving power densities of 2,401 mW cm⁻², which was 3.3 times higher than the control, and between 1.7 and 8 times higher to that obtained in the previous works herein discussed. Finally, Luo et al. [123] modified the ZIF-8 with FeS to dope the resulting carbon material with Fe, N, and S heteroatoms. This modified material had a BET surface area of 598 m² g⁻¹, and the presence of heteroatoms improved the power density of a MFC, displaying a maximum value of 1,196 mW cm⁻² with an OCV of 0.71 V.

      On the other hand, the use of MOF for the preparation of enzymatic electrodes is limited. Li et al. [124] developed an enzymatic BFC encapsulating laccase in the ZIF-8 MOF. This electrode array was combined with bacterial cellulose and carboxylated carbon nanotubes achieving OCVs close to 0.3 V, and a maximum current density of 3.68 W m⁻³. Zhang et al. [125] reported the use of the IRMOF-8 impregnated in carbon nanotubes to develop a porous carbon intercalated by multi-walled carbon nanotubes (PC/MWCNTs) as anode for the immobilization of alcohol dehydrogenase. This material had a BET surface area of 1,166 m² g-¹, while СКАЧАТЬ