A sustainable iron catalyst for water oxidation in renewable energy

Water oxidation plays a vital role in renewable energy technologies, especially in hydrogen production and artificial photosynthesis. By splitting water into oxygen and hydrogen, it provides a clean, sustainable energy source. However, replicating the efficiency and stability of natural photosynthetic systems in artificial catalytic setups -- especially in aqueous environments -- remains a significant challenge. Catalysts based on rare and expensive metals like ruthenium have shown high activity for water oxidation but are not practical for large-scale use due to their cost and limited availability.

To address this, a team of researchers led by Professor Mio Kondo from Institute of Science Tokyo (Science Tokyo), Japan,developed a more sustainable and cost-effective catalytic system using abundant metals. Their findings were published in Nature Communications on [Date].

The study introduces a novel pentanuclear iron complex, Fe5-PCz(ClO₄)₃, which possesses a multinuclear-complex-based catalytically active site and precursor moieties for charge transfer sites. Kondo explains, "By electrochemically polymerizing this multinuclear iron complex, we create a polymer-based material that enhances electrocatalytic activity and long-term stability. This approach combines the benefits of natural systems with the flexibility of artificial catalysts, paving the way for sustainable energy solutions."

The researchers synthesized the Fe5-PCz(ClO₄)₃ complex using organic reactions like bromination, nucleophilic substitution, Suzuki coupling reactions, and subsequent complexation reactions. The synthesized complex was characterized by mass spectrometry, elemental analysis, and single-crystal X-ray structural analysis. The researchers then modified glassy carbon and indium tin oxide electrodes by polymerizing Fe5-PCz using cyclic voltammetry and controlled potential electrolysis to afford a polymer-based catalyst, poly-Fe5-PCz. The charge transfer ability and electrocatalytic performance of poly-Fe5-PCz were evaluated through electrochemical impedance spectroscopy and oxygen evolution reaction (OER) experiments with oxygen production quantified by gas chromatography, respectively.

The results were highly promising. Kondo explains, "Poly-Fe5-PCz achieved up to 99% Faradaic efficiency in aqueous media, meaning nearly all the applied current contributed to the OER. The system also exhibited superior robustness and a reaction rate under rigorous testing conditions compared to relevant systems. Additionally, poly-Fe5-PCz demonstrated enhanced energy storage potential and improved electrode compatibility, making it suitable for a wide range of renewable energy applications." Its high stability was further confirmed by long-term controlled potential experiments, a key advantage for hydrogen production and energy storage technologies.

The study's findings have significant implications for sustainable energy. The use of iron -- an abundant, non-toxic metal -- ensures the system is both eco-friendly and cost-effective, offering a viable alternative to precious metal-based catalysts. Its stability under operational conditions addresses a major challenge in artificial catalytic systems, where long-term catalyst degradation often limits performance. Moreover, the system's performance in aqueous environments makes it suitable for applications in water splitting.

"Optimizing poly-Fe5-PCz synthesis and scalability could further enhance its performance, paving the way for industrial-scale hydrogen production and energy storage. Our study opens new possibilities for integrating the system into broader energy technologies, paving the way to a more sustainable future," concludes Kondo.