KENTECH Proposes Electrolyte Engineering to Revive ‘Dead Catalysts’

This post is also available in:

Breakthrough in Ammonia-based Room-temperature Hydrogen Production with a ‘Regeneration’ Strategy Instead of Catalyst Replacement

While ammonia-based hydrogen production has gained attention as a next-generation energy solution for its efficiency in storage and transportation, the rapid decline in catalyst performance—known as deactivation—has been the biggest obstacle to commercialization. Addressing this limitation, researchers at the Korea Institute of Energy Technology(KENTECH) have presented a new interpretation: catalyst deactivation is not permanent destruction but a temporary contamination arising from the electrolyte environment. Based on this, they have introduced a solution through electrolyte engineering.

Ammonia-based hydrogen production via conventional thermal decomposition faces structural limitations, requiring high temperatures above 500°C, which leads to high energy consumption and costs. Consequently, photoelectrochemical(PEC) ammonia oxidation, which utilizes both solar energy and electricity, has emerged as an alternative capable of producing hydrogen at room temperature and low voltage. However, repeated reports of rapid performance degradation in PEC environments have cast doubt on the technology’s sustainability.

Professor Wooyul Kim’s research team at KENTECH identified the cause of this catalyst deactivation not as permanent structural damage but as surface poisoning caused by nitrogen oxide($NO_x$) intermediates formed in water-based electrolyte environments. In other words, the catalyst is not ‘dead’ but merely in a state where its function is temporarily suppressed by reaction byproducts. This interpretation fundamentally challenges the existing assumption that deactivated catalysts must be replaced.

Beyond identifying the cause, the team proposed a solution by altering the electrolyte environment. By applying acetonitrile(MeCN), a non-aqueous solvent, instead of the conventional water-based electrolyte, $NO_x$ accumulation on the bismuth vanadate($BiVO_4$) photoanode surface was effectively suppressed. This resulted in a hydrogen production efficiency up to 6.9 times higher than under aqueous conditions. Notably, a ‘catalyst regeneration’ phenomenon was confirmed, where catalysts with already degraded performance recovered to near-initial levels when switched to the MeCN environment.

Experimental results showed that while $BiVO_4$ electrodes in water-based electrolytes lost approximately 90% of their photocurrent within one hour, no structural damage was observed. This supports the researchers’ interpretation that deactivation is surface contamination rather than destruction. Using operando surface-enhanced infrared absorption spectroscopy(operando ATR-SEIRAS), the team analyzed the reaction process in real-time. In aqueous environments, strong signals for nitric oxide($NO$) and nitrogen dioxide($NO_2$) appeared, whereas in the MeCN environment, these signals vanished, and ammonia and hydrazine($N_2H_4$) intermediates became dominant.

The catalyst regeneration effect following the electrolyte switch was also evident in actual hydrogen production. While cumulative hydrogen production in water-based conditions stagnated at approximately 5 $\mu$mol, it surged to 28 $\mu$mol when the fatigued catalyst was switched to an anhydrous MeCN environment. Electrochemical impedance spectroscopy(EIS) analysis further showed that the charge transfer resistance, which had increased significantly in water, decreased after the switch to MeCN, indicating the recovery of charge transfer at the electrode-electrolyte interface.

Meaningful results were also confirmed in terms of long-term stability. Under MeCN conditions, the $BiVO_4$ photoanode maintained about 82% of its initial current even after 20 hours of continuous operation, with a hydrogen Faradaic efficiency reaching 86%. This serves as an indicator of the potential for application in actual hydrogen production systems requiring long-term operation.

These experimental findings were further supported by theoretical calculations. Density functional theory(DFT) analysis revealed that even trace amounts of water make the $NO_x$ formation pathway dominant. In contrast, in a virtually anhydrous MeCN environment, a more favorable reaction path leading to $N_2H_4$ and $N_2$ via the coupling of $NH_2$ radicals becomes dominant. This suggests that controlling water activity within the electrolyte can fundamentally alter the reaction pathway itself.

Based on these achievements, the research team proposed a new operational strategy: instead of treating catalysts as consumables to be replaced, the electrolyte environment can be periodically controlled to self-clean and revive the catalysts. This concept demonstrated versatility beyond $BiVO_4$, showing similar stability improvements in various metal oxide photoanodes such as tungsten oxide($WO_3$) and hematite($\alpha-Fe_2O_3$).

Professor Wooyul Kim emphasized that electrolyte engineering, which precisely controls water activity, is a key technology for simultaneously achieving $NO_x$ poisoning suppression and catalyst regeneration. He anticipated that this would contribute to extending the lifespan and reducing maintenance costs for decentralized hydrogen production devices and renewable energy-linked hydrogen stations.

This study was led by KENTECH researchers in collaboration with the Korea Institute of Science and Technology(KIST) and Kyungpook National University. The results were published in Angewandte Chemie International Edition, a prestigious international journal issued by the German Chemical Society. By structurally reinterpreting catalyst stability in ammonia-based hydrogen production and solar-linked electrolysis, this research is expected to significantly influence future technology development.