(Invited) Enzymatic Reduction of Oxygen for the Development of Biofuel Cells and Hybrid Fuel Cells
Authors: Cosnier Serge 
Published: February 2020

The need for clean methods of producing electricity for medical applications has stimulated the emergence of biofuel cells as a new generation of fuel cells. This subcategory of fuel cells, mainly rely on redox enzymes, which are very efficient and selective biocatalysts that can advantageously replace rare and expensive platinum-based catalysts in classic fuel cell devices. Enzymes provide exceptional specificities towards their substrates, thus enabling the assembly of both the anode and cathode electrodes of a biofuel cell without the need for membranes [1,2]. Recent advances in the design of biocathodes based on electrically wired enzymes onto carbon nanotube coatings for the reduction of oxygen will be reported. In particular, different strategies for achieving a controlled orientation of laccase or bilirubin oxidase on carbon nanotube-based electrodes will be presented [3,4].

In particular, a new generation of flexible buckypaper electrodes was produced by using linear polynorbornene polymers containing multiple pyrene groups as crosslinker. Robust buckypapers using copolymers containing both pyrene and activated ester groups for cross-linking and tethering, respectively, will be applied to the covalent binding of redox groups or enzymes [5]. Moreover, buckypapers based on bilirubin oxidase and FAD-dependent glucose dehydrogenase, were developed for the direct electron transfer and the mediated electron transfer, respectively. The resulting biofuel cell based on the O2/glucose system, provides the highest volumetric power reported until now, namely 24.07 mW cm-3 [6].

The design of hybrid biofuel cells will be also reported. In particular, cubic Pd nanoparticles were synthesized and evaluated for the catalytic oxygen reduction. These nanoparticles were employed for the development of an air-breathing cathode modified by multiwalled carbon nanotubes. The latter was combined with a phenanthrolinequinone/glucose dehydrogenase-based anode to form a complete glucose/O2 hybrid biofuel cell delivering a maximal power output of 184 ± 21 µW cm-2 [7].

Finally, an innovative approach based on the electrical wiring of enzymes in solution by redox glyconanoparticles resulting from the self-assembly of bio-sourced block copolymers will be presented [8]. We demonstrate the self-assembly, characterization and bioelectrocatalysis of redox-active cyclodextrin-coated nanoparticles. The nanoparticles with host-guest functionality are easy to assemble and permit entrapment of hydrophobic redox molecules in aqueous solution. Bis-pyrene-ABTS encapsulated nanoparticles (diameter: 195 nm) were used as electron shuttles between electrode and bilirubin oxidase. Enhanced current densities for enzymatic O2 reduction are observed with the redox nanoparticle system compared to equivalent bioelectrode cells with dissolved mediator [9].

Acknowledgements

This work is partly supported by the French National Research Agency in the framework of the "Investissements d’avenir” program Glyco@Alps (ANR-15-IDEX-02), the LabEx ARCANE (ANR-11-LABX-0003-01), and Institut Carnot PolyNat (ANR-16-CARN-0025-01).

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. J. Gross, X. Chen, F. Giroud, C. Abreu, A. Le Goff, M. Holzinger, S. Cosnier, J. Am. Chem. Soc. accepted.