• Laheurte, Pascal
• Lohmuller, Paul
• Chauvet, Fabien
• Serrano, Karine Groenen
• Latapie, Laure
• Tzedakis, Theodore

Abstract

Electrochemical reactors play a key role in several fields (electrosynthesis, depollution, energy storage with redox flow batteries, etc.) where their intensification, and the enhancement of their selectivity, are an important issue that requires improving their mass transfer characteristics. For that purpose, porous or flow-through electrodes are generally integrated inside the compartments of reactors (metal foams, carbon felts, etc.). Recently, structured porous metal electrodes, fabricated by 3D printing, have been successfully integrated in electrochemical reactors [1]. The 3D printing offers several advantages for the design of electrodes: i) various materials available, ii) possibility to simulate numerically the fluid flow and the mass transfer (even current distribution), allowing optimization and tailoring of electrode structure by limiting or avoiding tests/prototypes. Here, we evaluate the electrochemical performance of 3D printed periodic lattice structures, originally known for their mechanical properties [2]. Two specific geometries have been considered: Diagonal and Octet-truss. The electrodes are fabricated by Selective Laser Melting (SLM) using a Ti alloy (TA6V) and integrated in a filter-press reactor. By feeding the reactor with a ferricyanide solution, the reduction signal of Fe(III) is measured by both linear sweep voltammetry and chronoamperometry. From the measurement of the limiting current, the volumetric mass transfer coefficient, kA_e, is determined for several flow rates (k: mass transfer coefficient, A_e: electrode surface area per unit of electrode volume). Very high values are obtained, in the range [0.1, 1s-1], that is equivalent and even better than carbon felts. With the aim to further optimize (or tailor) the electrode structure, the simulation of both fluid flow and mass transfer, through the 3D printed electrodes, was developed (Comsol). To lighten computations, the periodic property of these lattice structures is exploited by carrying out the simulation on only a part of electrode volume corresponding to a stack of unit cells. The obtained values of kA_e agree with the experiments. Additionally, we evaluate the role of the roughness, typically induced by the 3D printing process, on mass transfer. SEM analysis shows a roughness ~50µm (particle size used for SLM) which is close the average diffusion length ~10µm. By adding a model roughness, the simulation shows that the roughness induces an increase in kA_e of only a few %.[1] L.F. Arenas, C. Ponce de León, F.C. Walsh, Electrochemistry Communications, 77 (2017) 133–137 [2] P. Lohmuller, J. Favre, B. Piotrowski, S. Kenzari, P. Laheurte, Stress Concentration and Mechanical Strength of Cubic Lattice Architecture, Materials, 11 (2018) 1146

Topics

• porous
• impedance spectroscopy
• surface
• Carbon
• scanning electron microscopy
• experiment
• simulation
• strength
• selective laser melting
• chronoamperometry
• voltammetry
• metal foam