6 juillet 2021

[Nanotechnology] – High activity and durable oxygen evolution single atoms supported by tungsten carbide

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tungsten carbide - codex international

Hydrogen has been referred as the next-generation clean energy source for replacing fossil fuels, while its sustainable and scalable production is considered as the bottleneck for the development of proton exchange membrane fuel cells and hydrogen-fuel-cell vehicles.

One option is the production of hydrogen fuel by water electrolysis. However, to overcome the high overpotentials of water electrolysis, an efficient oxygen evolution catalyst is required.

Indeed, exploring new types of non-noble metal-based oxygen evolution and hydrogen evolution catalysts is one of the key tasks for the future development of a successful hydrogen economy.

In the past decades, although a series of oxygen evolution catalysts has been reported to show low overpotentials, the turnover frequency (TOF) values are still far away from satisfied.

For instance, the commercial noble-metal-based catalyst IrO2 usually shows a low TOF around 0.01 s-1, the widely investigated promising no-noble-metal catalyst FeNi-LDH only shows a TOF value around 0.05 s-1.

Therefore, there is an urgent need to further improve OER catalytic performances in terms of atomic activities and utilization rates to maximize the TOFs.

The most promising approach to maximizing the atomic utilization rates and synergistic effects between active sites is to disperse the catalytically active metal compounds down to the atomic level, that is, to prepare single-atom catalysts.

« However, the currently reported single-atom catalysts only show improvements in electrocatalytic reduction reactions, such as O2/CO2/N2 reduction and H2 evolution reactions. When applied in the OER, the single atom catalysts usually show insufficient activity and durability, » says Dr. Shuang Li, an electrocatalyst researcher and hybrid nanomaterials specialist at Technische Universität Berlin (Germany). « Hence, the development of highly active and stable single atom OER catalysts which show high TOF values is of crucial importance for the future application of water electrolysis. »

One major challenge in designing the high active single atom OER catalysts is that most of the current reported single atom catalysts are based on a strong heteroatom coordination environment to fix the single atom center.

However, this strong heteroatom coordination environment changes the electronic environment (d-band center) of the metal atoms through ligand effects, which are highly correlated with adsorbate binding energy and thus unfavorably influence the catalytic activity.

“Therefore, we are aiming at designing of highly durable and conductive support materials with well-defined structures that can stabilize catalytic metal atoms without the aid of strong heteroatom coordination, which is indeed a critical challenge.” says Dr. Li.

Taking this critical challenge, recently, the team from Prof. Chong Cheng at Sichuan University, Dr. Shuang Li and Prof. Arne Thomas at Technische Universität Berlin, and Dr. Yi Wang at Max Planck Institute for Solid State Research used metal carbides as the carrier to support the transition metal Fe and Ni atoms to engineer single-atom oxygen evolution catalysts for the first time.

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