(Invited) Water Electrolyzers for Green Hydrogen Production - a Tutorial on Catalyst and Electrode Development for Next Generation Devices

Abstract

Green hydrogen generation via electrolysis is at the forefront of international debates, with an unprecedent momentum within hydrogen technology. Various countries have already released their hydrogen strategy documents, recognizing the high propositional value of hydrogen as energy commodity of the future. Significant growth in water electrolysis has therefore occurred in recent years,` with the largest 20MW PEM electrolyzer being deployed for Iberdrola by NEL Hydrogen in Spain in 2021.This project shows how commercial polymer electrolyte membrane (PEM) electrolysis has reached scales of several hundred kg/day, providing a relevant pathway for industrial scale hydrogen generation. PEM electrolyzers also have tremendous potential for continuing cost reduction, leveraging system and manufacturing scaling laws as well as leveraging advancements in nanomaterials, advanced manufacturing tools, and both in-situ and ex-situ analysis tools. Order of magnitude improvements in some of the highest cost elements have already been achieved, including by NEL Hydrogen. Many of the technology elements such as PFSA membranes, iridium electrodes, porous transport layers, etc. are known, but still need to be refined and validated in a manufacturing environment at scale, including modifications in materials and novel yet economical methods of fabrication. At the same time, classic KOH based alkaline electrolyzers (AEL) are showing renewed promise, as diaphragm structure has advanced and understanding of electrode processing has developed. The basic environment of the alkaline electrolysis cell enables a broader range of materials and the potential to eliminate the highest cost materials such as platinum group metals and commercially pure titanium from the stack.However, for both AEL and PEM, complex interactions at the electrode level exist which need to be considered in catalyst and membrane/diaphragm development. First, the liquid electrolyte environment used for catalyst activity screening, where all the catalyst surface is accessible to the reactant is often not comparable to a complex, 3-dimensional, ionomer-based electrode. Therefore, in the same way that future alkaline electrode/diaphragm structures might resemble PEM catalyst coated membranes, novel PGM-free components still ought to show durability profiles similar to those shown by AEL stacks. This talk will describe some of the complex interactions that need to be considered, typical operating requirements, and stages of development where relevant conditions should be introduced.