The limited reservoir of fossil fuels and the ever increasing threats of climate change have encouraged researchers to develop alternative technologies to produce environmentally friendly fuels. Green hydrogen generated from the electrolysis of water using renewable electricity is seen as a next-generation renewable energy source for the future. But in reality, the overwhelming majority of hydrogen fuel is obtained from the refining of fossil fuels due to the high cost of electrolysis.
Currently, the efficiency of water electrolysis is limited and often requires high cell voltage due to the lack of efficient electrocatalysts for hydrogen evolution reactions. Noble metals such as platinum (Pt) are used as catalysts to improve hydrogen generation in both acidic / alkaline media. However, these noble metal catalysts are very expensive and exhibit poor stability during long term operation.
Recently, single atom catalysts have shown excellent activity compared to their nanomaterial based counterparts. Indeed, they are able to achieve up to 100% atom utilization, while in nanoparticles, only surface atoms are available for the reaction. However, due to the simplicity of the center of a single metal atom, it is quite difficult to perform further modification of the catalysts to perform complex multi-step reactions.
The easiest way to modify single atoms is to turn them into single atom dimers, which combine two different single atoms. Adjusting the active site of single atom catalysts with dimers can improve reaction kinetics due to the synergistic effect between two different atoms. However, while the synthesis and identification of the structure of the single atom dimer was conceptually known, its practical realization has been very difficult.
This problem was addressed by a research team led by Associate Director LEE Hyoyoung of the Center for Integrated Nanostructure Physics within the Institute for Basic Science (IBS) located at Sungkyunkwan University. The IBS research team successfully developed an atomically dispersed Ni-Co dimer structure stabilized on a nitrogen-doped carbon support, which was named NiCo-SAD-NC.
âWe synthesized a single atom Ni-Co dimer structure on a nitrogen (N) doped carbon support via in situ trapping of Ni / Co ions in the polydopamine sphere, followed by pyrolysis with precisely controlled N coordination. We used state-of-the-art transmission electron microscopy and X-ray absorption spectroscopy to successfully identify these NiCo-SAD sites with atomic precision, âsays Ashwani Kumar, the study’s first author. .
The researchers found that a two hour annealing at 800 Â° C in an argon atmosphere was the best condition to obtain the dimeric structure. Other single atom dimers, such as CoMn and CoFe could also be synthesized using the same method, which proves the generality of their strategy.
The research team evaluated the catalytic efficiency of this new system in terms of the surge required to drive the hydrogen evolution reaction. The NiCo-SAD-NC electrocatalyst had a surge level comparable to that of commercial Pt-based catalysts in acidic and alkaline media. NiCo-SAD-NC also exhibited 8 times higher activity than single atom Ni / Co catalysts and heterogeneous NiCo nanoparticles in alkaline medium. At the same time, it achieved 17 and 11 times higher activity than single atom Co and Ni catalysts, respectively, and 13 times higher than conventional Ni / Co nanoparticles in acidic medium.
In addition, the researchers demonstrated the long-term stability of the new catalyst, which was able to conduct a reaction for 50 hours without any structural change. NiCo-SAD exhibited superior water dissociation and optimal proton adsorption compared to other single atom dimers and single atom Ni / Co sites, increasing the activity of the pH-universal catalyst based on the simulation of the functional theory of density.
âWe were very happy to discover that the new NiCo-SAD structure dissociates water molecules with a much lower energy barrier and accelerates the reaction of hydrogen release in alkaline and acidic media with performance comparable to that of Pt. , which corrects the shortcomings of the individual Ni. and the single-atom catalysts of Co. Synthesis of such a single-atom dimer structure has been a long-standing challenge in the field of single-atom catalysts, ânotes Associate Director Lee, the corresponding author. of the study.
He further explains: âThis study brings us closer to a green, carbon-free hydrogen economy. pure hydrogen for commercial applications at low cost and in an environmentally friendly manner. “
The study was published in Nature Communication (IF 14.92), a world-renowned journal in the field of basic sciences.
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