Breakthrough in Affordable, Efficient Green Hydrogen Production

Abstract

Hydrogen production through anion-exchange membrane water electrolyzers (AEMWEs) offers cost advantages over proton-exchange membrane counterparts, mainly due to the good oxygen evolution reaction (OER) activity of platinum-group-metal-free catalysts in alkaline environments. However, the electrochemical oxidation of ionomers at the OER catalyst interface can decrease the local electrode pH, which limits AEMWE performance. Various strategies at the single-cell-level have been explored to address this issue. This work reviews the current understanding of electrochemical ionomer oxidation and strategies to mitigate it, providing our perspective on each approach. Our analysis highlights the competitive adsorption strategy as particularly promising for mitigating ionomer oxidation. This Perspective also outlines future directions for advancing high-performance alkaline AEMWEs and other energy devices using hydrocarbon ionomers.

The principle of preventing the deterioration and oxidation of ionomers in hydrogen production through anion-exchange membrane water electrolyzers (AEMWEs) has been discovered for the first time. This breakthrough is expected to enhance both the performance and durability of hydrogen production devices.

A research team, led by Professor Seung Geol Lee in the Department of Materials Science and Engineering at UNIST has introduced a novel AEMWE technology that employs an inexpensive non-platinum metal catalyst. By enabling potassium to adhere to the catalyst surface, this method minimizes direct contact with the ionomer, potentially reducing the cost of hydrogen production.

In typical hydrogen production devices, the properties of ions that facilitate ionic transport tend to degrade over time, resulting in decreased hydrogen production efficiency and a shortened device lifespan.

The research team capitalized on the fact that the adsorption energy of potassium is more than three times greater than that of organic compounds. Their findings indicate that substances such as potassium hydroxide and sodium hydroxide can significantly improve the performance and stability of the AEMWE system.

By adsorbing cationic materials onto the catalyst surface, the direct contact between the ionomer and the catalyst is reduced. This mechanism was validated using density functional theory (DFT), which calculates the electronic structure of materials, thereby demonstrating that ionomer oxidation can be prevented while maintaining hydrogen production performance.

While previous attempts to enhance performance using aqueous potassium hydroxide and sodium hydroxide solutions with high basicity have not elucidated the underlying principles, the competitive adsorption strategy identified in this study holds promise for advancing the commercialization of low-cost catalysts.

Researcher Jihoon Lim, the first author, stated, "The competitive adsorption strategy effectively reduces the electrochemical oxidation of ionomer materials at the interface with the catalyst."

Professor Lee remarked, "This study sets a path for improving the performance and stability of various energy devices, including high-performance alkaline AEMWE systems."

The findings were published online in ACS Energy Letters on June 2, 2024. This research was a collaborative effort with Dr. Yu Seung Kim and his team at Los Alamos National Laboratory (LANL) in Los Alamos, New Mexico and Professor Shannon Boettcher at the University of California, Berkeley and the Lawrence Berkeley National Laboratory in Berkeley, California, United States, with support from the U.S. Department of Energy and the National Research Foundation of Korea (NRF).

Journal Reference

Jihoon Lim, Jeffrey M. Klein, Seung Geol Lee, et al., "Addressing the Challenge of Electrochemical Ionomer Oxidation in Future Anion Exchange Membrane Water Electrolyzers," ACS Energy Lett., (2024).