Abstract
This study explored the multifaceted role of flavin adenine dinucleotide (FAD) in modulating proton-coupled electron transfer (PCET) processes for electrocatalysis. FAD demonstrated catalyst-dependent functionality, enhancing hydrogen evolution reaction (HER) on Pd and facilitating formic acid oxidation reaction (FAOR) on Pt through selective modulation of hydrogen coverage. FAD scavenged H* on Pt, promoting FAOR, while boosting H⁺ adsorption on Pd, driving HER. Additionally, FAD-modified Pd membranes enabled efficient hydrogen spillover, achieving toluene hydrogenation into methylcyclohexane (MCH as a liquid organic hydrogen carrier) under mild conditions. These findings emphasized FAD's versatility as a molecular PCET modulator, paving the way for improved electrocatalytic systems in hydrogen production and hydrocarbon hydrogenation.
A research team, affiliated with UNIST has unveiled a novel system to produce green hydrogen more cost-effectively by harnessing a biological energy coenzyme to reduce electrical energy consumption. Furthermore, this technology enables direct storage of hydrogen within liquid organic compounds without the need for prior conversion into gas, promising substantial reductions in both production and transportation costs.
Led by Professor Hyun-Kon Song in the School of Energy and Chemical Engineering at UNIST, the research team designed an electrochemical system that utilizes flavin adenine dinucleotide (FAD)-a coenzyme vital in cellular energy metabolism-to generate and immediately store hydrogen in liquid organic forms at low voltage.
The system features electrodes made of platinum (Pt) and palladium (Pd). During operation, formic acid (HCOOH) is oxidized on the platinum electrode, releasing electrons that travel to the palladium electrode, where hydrogen ions (H⁺) combine with these electrons to form atomic hydrogen (H*). This hydrogen then permeates through a palladium membrane directly into an attached liquid organic medium for storage.
Figure 1. Schematic illustration of FAD-driven electrocatalysis for selectively modulating PCET mechanisms on Pt and Pd catalysts.
By applying FAD to both electrodes, the team enhanced the efficiency of hydrogen production while significantly reducing the electrical energy needed. Notably, the cell operated effectively at an ultra-low voltage of approximately 0.6V-a reduction of about 65% compared to conventional systems.
The system also demonstrated remarkable durability, maintaining performance for over 100 hours of continuous operation-eight times longer than typical setups-without degradation. This longevity is crucial, as higher operating voltages tend to increase power consumption and shorten device lifespan.
A key advantage of this technology is the elimination of the need for separate processes to compress or handle gaseous hydrogen. As explained by first author Jisu Lee, "Instead of producing hydrogen gas (H₂) and then pressurizing or reacting it further, our system directly stores hydrogen atoms (H) generated at the electrode surface into liquid organic compounds, simplifying the process and improving safety."
FAD, a coenzyme naturally found in mitochondria to assist in energy production, possesses the unique ability to transfer both electrons and protons. In this system, it plays a tailored role: on palladium, it promotes hydrogen atom attachment to the electrode surface, while on platinum, it facilitates the removal of intermediate hydrogen species, ensuring smooth and efficient reactions on both sides.
Figure 2. Schematic diagram illustrating the overall study involving FAD.
Professor Song emphasized, "By integrating the electron and proton transport capabilities of biological molecules like FAD into electrochemical systems, we have simultaneously addressed hydrogen production and storage. This innovation offers a safe, efficient, and low-cost approach to hydrogen energy, without the need for high-pressure tanks."
Their findings have been published online in Applied Catalysis B: Environmental and Energy on July 2, 2025. It was supported by the InnoCore Program of UNIST Hydro*Studio, as well as funding from the Ministry of Trade, Industry and Energy (MOTIE), Korea Institute for Advancement of Technology (KIAT), and the National Research Foundation of Korea (NRF).
Journal Reference
Jisu Lee, Hosik Lee, Do Sol Cheong, et al., "FAD-mediated modulation of hydrogen adsorbates for low-voltage hydrogen production and hydrocarbon hydrogenation," Appl. Catal. B: Environ., (2025).
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