Researchers at Mainz University have developed cost-effective and efficient water-splitting catalysts to be used in the eco-friendly production of hydrogen / Catalyst performance surprisingly increases over time
Hydrogen is a much-debated option in terms of CO₂-neutral energy production. Electrolyzer units that split water into its constituent oxygen and storable hydrogen are supplied with electricity from renewable resources, mainly generated by wind and solar energy. However, catalysts are necessary to facilitate this process. To date, noble metal oxides such as ruthenium dioxide and iridium dioxide are being used as benchmark catalysts. These metals, however, are expensive, rare, and unstable in both acidic and alkaline environments.
Dr. Dandan Gao, a junior group leader at Johannes Gutenberg University Mainz (JGU) and holder of a Walter Benjamin Fellowship sponsored by the German Research Foundation, and her team have managed to devise an alternative form of catalyst using cobalt and tungsten, elements that are readily available at low cost. "What's so unique about our catalyst is that it actually enhances its performance over time, while conventional catalysts either maintain their performance at a consistent rate or even lose some of their performance because they are insufficiently durable," stated Dr. Dandan Gao. "After the process of optimization, activity is even higher than that of benchmark catalysts." The results of Gao and her team have recently been published in the international edition of the journal
Angewandte Chemie.
What causes the self-optimization process?
The researchers undertook experimental and theoretical investigations to find an explanation for the extraordinary self-optimization of their catalyst. They were able to determine that the chemical nature of the catalyzing cobalt-tungsten oxide changes during the process of water-splitting. While the cobalt is initially largely present in the form of Co²⁺, it is increasingly converted to Co³⁺. At the same time, the proportion of the original tungsten W⁵⁺ ion to the W⁶⁺ ion shifts in favor of the latter. "There are two reactions during the splitting of water. The hydrogen evolution reaction (HER), which produces hydrogen gas, and the oxygen evolution reaction (OER), which produces oxygen gas. The OER represents the bottleneck for the whole reaction," explained Gao. "That's why we are so committed to developing a catalyst that can promote the OER half reaction."
While the OER is initially induced by the tungsten active site, this process is transferred with time to the cobalt active site. Moreover, the electrochemically active surface area of the catalyst also increases over the course of time. The research team also observed alterations to the hydrophilicity of the surface. Its affinity for water increases progressively, which is particularly beneficial in the context of electrochemical water-splitting. "In general, we recorded notably reduced overpotentials and increased current densities accompanied by a substantial increase in OER kinetics," concluded Gao. All this is positive news for the hydrogen production of the future.
Funding by the Walter Benjamin Program of the German Research Foundation
Dandan Gao has been sponsored through the Walter Benjamin Program of the German Research Foundation (DFG) since June 2023. This program enables early career researchers to pursue their own research project at an institution of their choice. The host research institution – Johannes Gutenberg University Mainz in this case – provides support for the project in question.
The work outlined in Angewandte Chemie also received support from the Carl Zeiss Foundation, the Alexander von Humboldt Foundation, and JGU's Top-level Research Area SusInnoScience –Sustainable Chemistry as the Key to Innovation in Resource-efficient Science in the Anthropocene.
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