Investigation on Electrochemical Reaction for Anion Exchange Membrane Electrode Assembly-Based Electrolyzer
Authors: Han Gyeong Ho , Ahn Sang Hyun 
Published: December 2024

Although the use of fossil fuels is gradually decreasing every year, it still accounts for more than 80% of global energy consumption, and discriminatory use is causing a significant increase in atmospheric CO2 concentration and global warming. In order to control the indiscriminate use of fossil fuels that cause environmental problems, establishing an eco-friendly energy conversion system is essential. The water electrolysis using surplus power generated from renewable energy is recognized as a representative system that can produce high-purity hydrogen from water. On the other hand, CO2 electrolysis is also a promising energy conversion technology that can reduce atmospheric CO2 centration because it electrochemically converts CO2 into valuable carbon products. Both of the above systems are based on electrochemical reactions, which means they can operate under moderate conditions with zero pollutant emissions.

In general, the composition of conventional energy conversion system includes an electrolyte layer, which has a large ohmic resistance and limitation of CO2 solubility, which reduces energy efficiency. To address the disadvantage of the conventional system, membrane electrode assembly (MEA)-based electrolyzer are receiving attention. The MEA consists of an electrode and a membrane with a polymer membrane capable of ion exchange between the anode and the cathode. These MEA-based electrolyzer has a zero-gap configuration, providing minimized ohmic resistance and improved energy efficiency. Among them, various studies are being actively conducted on applying an anion exchange membrane (AEM) to MEA-based electrolyzers. When using AEM, water electrolysis has the advantage of being able to use a non-noble metal catalyst, which can reduce costs, and CO2 electrolysis has the advantage of reducing the hydrogen evolution reaction (HER), which is a competing reaction.

Herein, the electrode with a structure in which electrocatalyst is loaded on a porous transport layer (PTL) is fabricated by the facile electrodeposition method. The electrodeposition is possible to fabricate self-supported electrodes by modulating catalytic properties such as morphology, composition, and crystallinity by controlling various parameters. Additionally, ionomer and binder-free electrode structure prepared through electrodeposition contributes to improving catalytic performance by promoting electron transfer to the active site. Moreover, the as-prepared porous transfer electrodes (PTE) are used as cathode and anode in anion exchange MEA-based electrolyzer and exhibit reasonable single-cell performance, suggesting that PTEs prepared via electrodeposition are suitable for energy conversion systems such as water electrolysis and CO2 electrolysis.

In the MEA configuration, three cathodes, anodes, and AEM were optimized. In the cathode part, the HER was optimized using catalysts such as NiMo, Pt, and PtRu, and the CO2 electrolysis was optimized using Au, Ag, Cu, and Pd. In the anode part, the oxygen evolution reaction (OER) was optimized using catalysts such as NiFe, IrO2. In the membrane part, optimization was performed by comparing the commercial membrane and the fabricated fluorine-containing poly(fluorene)-based AEM.