Enzymatic H₂/O₂ fuel cells (EFC) recently emerged as attractive devices for small power applications [1]. In this “green” fuel cell, hydrogenase and multicopper oxidase enzymes would replace scarce and expensive chemical catalysts at the anodic and cathodic sides respectively. Advantages of biocatalysts include bioavailability, high specificity that allows to avoid the costly membrane separator between the two cell compartments, high efficiency, very low over-voltages for the transformation of the substrates. Screening the biodiversity allows furthermore to identify enzymes showing outstanding properties, such as thermostability and insensitivity to CO which is one of the major drawback of the platinum catalyst used in fuel cells. [2].

One of the main challenges to EFC development is to achieve high power performances and stability in order EFCs become a self-sufficiency source of energy. The first issue is to optimize the electron transfer rate between the enzyme and the electrochemical interface. This will allow to improve the turn over frequency of the immobilized enzyme, thus the catalytic current under a low overvoltage. The second issue is to enhance the loading of electrically connected enzymes to reach catalytic currents compatible with a practical application. These two issues suppose i) the knowledge of the electron pathways from the enzyme active site to the electrode, ii) the knowledge of the key amino acid residues involved in the interfacial recognition, and iii) the development of biocompatible 3D networks. Previous works in our laboratory have shown how the combination of electrochemistry, PMIRRAS and modeling helps in the understanding of the modular basis for such an efficient enzyme immobilization on planar electrochemical interfaces. We were then able to design the first H₂/O₂ biofuel cell delivering a power density of 300 µW.cm^-2 [3].

In this work we discuss the rational design of nanostructured interfaces able to enhance the performances of the H₂/O₂ biofuel cells [4]. We show that coupling electrochemistry to SPR provides essential kinetic data to get a full understanding of the electron process as a function of various parameters (chemistry of the electrochemical interface, pH, time, applied potential,…). We highlight that gold nanoparticles and various carbon nanomaterials, from nanotubes to nanofibers, can serve as efficient platforms for enzyme immobilization with enhanced long-term stability. We especially focus on the hierarchical porosity and the chemical functionalization of the nanomaterials. Their respective role on mass transport limitation during catalysis and stable loading of the biocatalyst is discussed as a function of the nature of the enzyme. We then develop new strategies based on modification of carbon felts by these nanomaterials. The performances of the new H₂/O₂ biofuel cells based on these optimized biohybrids are presented. We demonstrate that these EFCs deliver a cell power required to feed a wireless electronic device [5-6].

References

(1) A. de Poulpiquet et al., ChemElectroChem, (2014)

(2) M. Guiral et al., Adv. Microbial. Physiol., (2012)

(3) A. Ciaccafava et al., Angew. Chem. (2012) ; Electrochem. Comm. (2012)

(4) K. Monsalve et al., Bioelectrochem. (2015) ; A. de Poulpiquet et al., PCCP (2014)

(5) A. de Poulpiquet et al., Electrochem. Com., (2014) ; N. Lalaoui et al., Chem. Comm. (2015) ; K. Monsalve et al., Electrochem. Comm. (2015)