Fabrication of Highly Uniform and Durable Co 3 O 4 for AEMWE through an Optimized Electrode Fabrication

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As the climate crisis intensifies, green hydrogen has emerged as a key eco-friendly energy source that can reduce fossil fuel dependence and curb carbon emissions. Among various hydrogen production strategies, anion exchange membrane water electrolysis (AEMWE) has gained considerable attention for its ability to produce high-purity hydrogen using inexpensive, non-precious metal catalysts. AEMWE anodes can be fabricated through either self-supported or slurry casting approaches. When non-precious metal catalysts are used as the anode, their intrinsic activity and durability are lower than those of precious metal catalysts. Consequently, to achieve equivalent hydrogen production, higher catalyst loadings and larger electrode sizes are required. Moreover, to ensure economic viability, large-area stack cells must be produced, making slurry coating—particularly the binder-based decal method—well-suited for the industrial-scale fabrication of CCS and CCM-type MEAs, thanks to its flexible catalyst loading and straightforward scalability. However, in the slurry casting process, particularly when applying the decal method, parameters such as catalyst slurry properties and hot-pressing conditions can significantly influence the electrode’s uniformity and performance. Excessive pressure to prevent delamination of the catalyst layer may collapse pores in the electrode, increasing mass transfer resistance, whereas insufficient binding force can allow bubbles formed during operation to detach the catalyst layer. Consequently, achieving both stability and structural integrity of the catalyst layer in decal-processed electrodes is challenging. To address these issues, we developed a one-step hot-pressing process that leverages a phase transition triggered by oxidative heat treatment during the transfer process, enabling the integral fabrication of dense, stable, and highly porous electrodes. Through this process, Co(OH) 2 slurry undergoes a phase transformation into Co 3 O 4 in a high-pressure environment, significantly enhancing the bonding among catalyst particles and between the catalyst and the substrate. Furthermore, the structural changes accompanying this phase transition induce pore formation, effectively overcoming the limitations of conventional slurry casting methods. As a result, Co(OH) 2 slurry-based Integreated oxidized electrode (In-CO) exhibited a more uniform electrode surface, robust adhesion, and consistent pore area compared to Co 3 O 4 slurry-based Pre-oxidized electrodes (Pre-CO). Also, In-CO exhibited a high single-cell performance of 3.25 A cm -2 —an approximately 12% improvement over Pre-CO. Moreover, after 500 hours of operation at 0.5 A cm -2 , the electrode showed a degradation rate of only 17.5 mV kh -1 —around 20% of that observed in Pre-CO—highlighting its excellent durability.

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