Flow-engineered 3D printed electrodes for enhanced bubble evacuation during alkaline water electrolysis

A zero-gap cell with porous electrodes is a promising configuration for alkaline water electrolysis. However, bubble evacuation becomes a challenge in that case, as bubbles can get trapped within the electrode’s 3D structure 1. This work considers a number of 3D printed electrode geometries with so-called triply periodic minimal surfaces (TPMS). The latter is a mathematically defined structure based on a void fraction and a lattice parameter that repeats itself in three dimensions with zero mean curvature, and can therefore be expected to be particularly well-suited to enhanced bubble evacuation 2. Another advantage as compared to other stochastic 3D electrodes like foams or felts lies in the fact that their porosity, which determines the available surface area, and their pore size or flow channel dimensions, which determines the degree of bubble entrapment, can be varied independently. Firstly, the electrochemical performance of 3 types of TPMS geometries (so-called gyroids, Fisher-Koch and Schwarz structures) has been measured under industrially relevant conditions (30 wt% KOH electrolyte at 80°C with a Zirfon Perl UTP 500 diaphragm) for both 3D printed pure and Raney Ni. In particular, their sensitivity with upstream electrolyte flow rate was studied. Experimental results were then compared with computational fluid dynamics (CFD) simulations and an in-situ visualization of the flow stream and bubble behavior, the latter using a dedicated home-built transparent electrolyzer. Initial results shown in Fig. 1 indicate that an optimal combination of these parameters allows, under a forced upstream electrolyte flow, for a reduction in cell overpotential of almost 20%. This indicates that efforts in optimizing the electrode’s geometry can give a similar electrochemical performance enhancement as optimizing its electro-catalytic composition.