How to Enhance Gas Removal from Porous Electrodes?

Abstract

This article presents a structure-based modeling approach to optimize gas evolution at an electrolyte-flooded porous electrode. By providing hydrophobic islands as preferential nucleation sites on the surface of the electrode, it is possible to nucleate and grow bubbles outside of the pore space, facilitating their release into the electrolyte. Bubbles that grow at preferential nucleation sites act as a sink for dissolved gas produced in electrode reactions, effectively suctioning it from the electrolyte-filled pores. According to the model, high oversaturation is necessary to nucleate bubbles inside of the pores. The high oversaturation allows establishing large concentration gradients in the pores that drive a diffusion flux towards the preferential nucleation sites. This diffusion flux keeps the pores bubble-free, avoiding deactivation of the electrochemically active surface area of the electrode as well as mechanical stress that would otherwise lead to catalyst degradation. The transport regime of the dissolved gas, viz. diffusion control vs. transfer control at the liquid-gas interface, determines the bubble growth law.

Correlating the Short-Time Current Response of a Hydrogen Evolving Nickel Electrode to Bubble Growth

“…Our measurements, thus, imply that the design of structured electrodes (by placing sites of bubble growth, i.e. hydrophobic nucleation sites, adjacent to catalytically active spots) would increase the cell efficiency, something that has been suggested in the past for porous electrodes, 22 and employed most recently in the context of bubbles by van der Linde et al 9,23 for planar electrodes.…”

Photosynthesis under very high oxygen concentrations in dense microbial mats and biofilms

“…Thus in clean water, the site of O 2 production (e.g. an electrode) O 2 levels must be ∼300 times higher than saturation, close to 2.5 M, before formation of bubbles can occur (17). This concentration is needed to overcome the surface tension of 260 atm of the initial bubbles.…”

Sequential catalysis controls selectivity in electrochemical CO2 reduction on Cu

“…However, supersaturation of a gas on the surface of an electrode from which it is produced is a well-known effect. [59][60][61][62][63] Notably, smooth electrode surfaces of the type we will employ here have been shown to suppress bubble nucleation, allowing for a high degree of supersaturation.…”