Synthesis of a cost-effective, high-durability non-noble metal alloy anode as an alternative to iridium oxide anodes

Tsukuba, Japan—Despite hydrogen's increasing prominence as a future energy source, the safe and large-scale transportation of gaseous hydrogen remains challenging. Researchers are exploring ways to transport hydrogen in the form of liquid methylcyclohexane (MCH) by reacting it with toluene. One such approach is organic hydride electrolytic synthesis. In this process, toluene is transferred from a cathode to an iridium oxide anode under highly acidic conditions. However, toluene oxidizes on the anode surface, forming a polymer coating that remarkably degrades the electrode's performance. This situation highlights the need for more durable and cost-effective anode materials.

In response, researchers at the University of Tsukuba developed a high-entropy alloy anode composed of nine non-precious metal elements using a conventional arc melting method. They also elucidated the mechanism underlying the catalytic poisoning by toluene, which considerably influences the anode durability in organic hydride electrolytic synthesis. Their findings reveal that benzoic acid, an oxidized form of toluene, contributes notably to polymerization and anode degradation. Hence, preventing the oxidation of toluene to benzoic acid is crucial because the benzoic acid could be a trigger for polymerization.

When used in organic hydride electrolytic synthesis, the high-entropy alloy anode required an additional 0.37 V for initial operations compared with conventional iridium oxide anodes which immediately degrade in the presence of toluene. However, the newly developed anode demonstrated remarkable durability and a low production cost of less than 50 yen/g. These attributes make it a promising alternative to iridium oxide anodes, potentially advancing the development of a large-scale hydrogen supply chain.

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This work was funded by the ENEOS Hydrogen Trust Fund; JSTPRESTO (Grant Number JPMJPR2115); JSPS Grant-in-Aid for Scientific Research on Innovative Areas 'High Entropy Alloys' (Grant Number JP19H05166, JP21H00140 and JP21H00153); The Iwatani Naoji Foundation; JSPS-Kakenhi (Grant Numbers JP21H02037, JP23K17661, JP22K18929 and JP24H00478); JACI Prize for Outstanding Achievements; NIMS microstructural characterization platform as a program of 'Nanotechnology Platform Project', MEXT, Japan (Grant Number: JPMXP09A20NM0013); the Open Facility, Research Facility Center for Science and Technology, University of Tsukuba; and a cooperative program (Proposal No. 202311-CRKEQ-0001) of the CRDAM-IMR, Tohoku University. DFT calculations were carried out using the facilities of the Supercomputer Center, Institute for Solid State Physics, and University of Tokyo. A.A.H.T. acknowledges the Japanese government for the MEXT-ASJA scholarship.

_{Original Paper}

Title of original paper:
Toluene-Poisoning-Resistant High-Entropy Non-Noble Metal Anode for Direct One-Step Hydrogenation of Toluene to Methylcyclohexane

Journal:
ChemSusChem

DOI:
10.1002/cssc.202401071

_{Correspondence}

Associate Professor ITO, Yoshikazu
Associate Professor TANIMOTO Hisanori
Institute of Pure and Applied Sciences, University of Tsukuba

Associate Professor OHTO, Tatsuhiko
Graduate School of Engineering, Nagoya University

Professor FUJITA, Takeshi
School of Engineering Science, Kochi University of Technology

_{Related Link}

Institute of Pure and Applied Sciences