Frederic Topin

Impact of substrate diffusion and enzyme distribution in 3D-porous electrodes: a combined electrochemical and modelling study of a thermostable H2/O2 enzymatic fuel cell

Using 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 thermostable enzymes 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 μm 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 porous electrode to be fully determined for the first time. High total turnover numbers, approaching 107 for BOD and 108 for hydrogenase, were found, as was an impressive massic activity of 1 A mg−1 with respect to the mass of the electroactive enzyme molecules. This strategy, relying on stable enzymes and mesoporous materials, and the model set up may constitute the basis for a larger panel of bioelectrodes and EFCs.

Micro-structural Impact of Different Strut Shapes and Porosity on Hydraulic Properties of Kelvin-Like Metal Foams

Various ideal periodic isotropic structures of foams (tetrakaidecahedron) with constant ligament cross section are studied. Different strut shapes namely circular, square, diamond, hexagon, star, and their various orientations are modeled using CAD. We performed direct numerical simulations at pore scale, solving Navier–Stokes equation in the fluid space to obtain various flow properties namely permeability and inertia coefficient for all shapes in the porosity range,

Influence of pore and strut shape on open cell metal foam bulk properties

0.60<varepsilon <0.95

Development of an Analytical-Oriented Extensive Model for AC Coupling Losses in Multilayer Superconducting Composites

0.60<ε<0.95 for wide range of Reynolds numbers,

Studying impacts of travelling wave shape on pumping for active cooling

10^{-6}<Re<3000

Multicellular piezoelectric actuator for setting in motion fluids, and heat exchange enhancement

10-6<Re<3000. We proposed an analytical model to obtain pressure drop in metallic foams in order to correlate the resulting macroscopic pressure and velocity gradients with the Ergun-like approach. The analytical results are fully compared with the available numerical data, and an excellent agreement is observed.