Impact of substrate diffusion and enzyme distribution in 3D-porous electrodes: a combined electrochemical and modelling study of a thermostable H₂/O₂enzymatic fuel cell

Abstract

International audienceUsing redox enzymes as biocatalysts in fuel cells is an attractive strategy for sustainable energy production. Once hydrogenase for H2 oxidation and bilirubin oxidase (BOD) for O2 reduction have been wired on electrodes, the enzymatic fuel cell (EFC) thus built is expected to provide sufficient energy to power small electronic devices, while overcoming the issues associated with scarcity, price and inhibition of platinum based catalysts. Despite recent improvements, these biodevices suffer from moderate power output and low stability. In this work, we demonstrate how substrate diffusion and enzyme distribution in the bioelectrodes control EFC performance. A new EFC was built by immobilizing two thermostableenzymes in hierarchical carbon felt modified by carbon nanotubes. This device displayed very high power and stability, producing 15.8 mW h of energy after 17 h of continuous operation. Despite the large available electrode porosity, mass transfer was shown to limit the performance. To determine the optimal geometry of the EFC, a numerical model was established, based on a finite element method (FEM). This model allowed an optimal electrode thickness of less than 100 mm to be determined, with a porosity of 60%. Thanks to very efficient enzyme wiring and high enzyme loading, non-catalytic signals for both enzymes were detected and quantified, enabling the electroactive enzyme distribution in the porouselectrode to be fully determined for the first time....

Controlling Redox Enzyme Orientation at Planar Electrodes

“…Indeed, thanks to the specificity and properties of some hydrogenases, it becomes possible to use nonpure H 2 , as hydrogen produced from biomass or waste. Recent research shows that high current densities in the order of 10 mA/cm 2 , and all the most high currents reported (up to 1 A per mg of enzyme) can be reached, which is very promising [21].…”

“…Agreement between the magnitudes of the catalytic current as a function of the surface chemistry on the carbon nanotubes with theoretical modeling of the dipole moment of the enzyme was also demonstrated [194]. Nevertheless, only a low percentage, around 10%, of the loaded enzymes were electrically connected in the 3D structure [21], which suggests that other parameters than a correct enzyme orientation for DET drive catalysis in 3D conductive structures. One should be aware of the heterogeneity of electrochemical interfaces such as those formed by carbon nanotubes or carbon particles.…”

“…Nonetheless, it is worth mentioning the original work of Vincent's group, who set up a Protein Film Infrared Electrochemistry (PFIRE) method for the monitoring of the enzyme conformation entrapped in carbon black particles [55]. Mazurenko et al also reported the resolution of enzyme partitions in carbon felts [21]. Nevertheless, it appears more relevant to study the immobilization of redox enzymes on more planar electrodes, to achieve easier control of the enzyme conformation, and to overcome mass transport and substrate partition issues arising from the surface meso-or nanoporosity which induces local variation of substrates and products (such as local acidification, for example) and complexifies the whole process.…”

Micro‐ and Nanoscopic Imaging of Enzymatic Electrodes: A Review

“…However, this latter is rarely detected. For example, only two publications relate its observation for the enzyme hydrogenase . Therefore, authors most of the time consider that enzyme quantity is below the electrochemical detection limit.…”

“…Tuning the overpotential applied to the electrode allows finely tuning the driving force of the electron transfer reaction, and therefore gives access to the thermodynamic and kinetic properties of the biomolecules as well as information about reaction mechanisms . Finally, the same methods give access to current‐voltage behavior that fully characterizes a bio‐fuel cell, and to sensitivity, precision, and specificity of a biosensor.…”