Engineering Electrodes with Bimodal Pore Size Distributions for Next-Generation Electrochemical Devices

Abstract

In many electrochemical conversion devices such as low temperature fuel cells or water electrolyzers, the transport of reactants to and products from the catalyst layer is facilitated by porous structures referred to as gas diffusion layers or porous transport layers. They bridge the gap between flow fields and catalyst layers and their mass transport capabilities become especially critical at high current density operation. Excessive accumulations of reaction products or a lack of fresh reagents stall out the electrochemical conversion resulting in reduced efficiencies or even damage to the system itself due to fuel starvation1. Thus, to realize cost-competitive electrochemical systems we must overcome the fundamental challenge of multiphase flows in which liquid and gaseous phases flow through porous structures in opposing directions.In recent years, porous electrodes have been adapted to better address these issues and improve performance. For example, the addition of a layer with reduced pore size facing the catalyst layer (i.e., micro porous layer) was shown to increase performance in fuel cells and electrolyzers2–4. Furthermore, chemical5 as well as mechanical6,7 methods of creating dedicated liquid and gas pathways in the structure have been investigated with promising results. These approaches are however intrinsically limited by the microstructure of the material they are applied to.Inspired by the success of these modifications, we propose a novel structure containing both a pore size gradient as well as dedicated water and gas pathways in the form of bimodal pore size distributions (Figure 1). This material is generated by depositing a metal in the presence of gas evolution to form a structure containing microscopic and macroscopic pores. This type of material has in the past been used successfully to improve boiling heat transfer8, another process faced with the counterflow of liquid and gas. They have also been investigated as high surface area material for microbial anodes9 and have been postulated to find application in other electrochemical devices such as batteries or fuel cells10. In this talk, I will discuss the synthetic approach to manufacture self-standing porous electrodes using an electrochemical flow platform and elucidate the correlation between applied electrochemical parameters and resulting material microstructure. Properties such as electrode thickness and pore sizes can be adjusted during the synthetic process to suit the requirements of specific applications exhibiting complex mass transport requirements.Acknowledgements:This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 899987.