Process intensification of alkaline water electrolysis by using 3-D electrodes

(eng) Hydrogen is a promising and well‐accepted energy vector to store electricity produced by intermittent sources, such as solar panels and wind turbines. In order to be cost effective, the water electrolysis needs to be intensified (higher production in smaller units) and scaled up to the match the power of electricity sources The current work focuses on a simple way to increase the efficiency of water electrolysis by the use of 3‐D electrodes and forced electrolyte flow. Such macro‐porous electrodes allow to reduce the cathodic overpotential compared to state of the art 2‐D plate electrodes. Under natural convection the produced gas bubbles tend to block the 3‐D structure reducing its benefit. Thanks to the forced flow, the gas bubbles are forced out of the 3‐D electrodes. A typical result is shown in Figure 1. According to the electrokinetic Butler‐Volmer equation, a higher current density requires a higher overpotential. Therefore, since for the same applied current the current density decreases with increasing specific electrode area, the required (over‐)potential to drive the macroscopic current will be lower for the 3‐D electrode compared to a 2‐D electrode. For this reason the use of 3‐D electrodes will reduce the cell voltage for a given applied current as it can be seen in Figure 1. In Figure 2, we can see the influence of the catholyte flow rate on the cell voltage. At lower flow rate (v1) the produced hydrogen bubbles tend to block the 3‐D structure of the electrode, reducing the surface area in contact with the electrolyte. Increasing the flow rate (v3 to v9) will force de bubbles out of the electrode allowing to take full advantage of their high surface area. Figures 1 and 2 were obtained in a benchtop laboratory experiment. Future work will focus on implementation of these results in a pilot plant setup. The latter has a size representative for an industrial production equipment. Our presentation will show the results of this scale‐up.