Two is better than one: Single-atom dimer electrocatalyst for green
hydrogen production
Nickel-cobalt metal dimer on nitrogen-doped carbon can catalyze
electrolysis under both acidic and basic conditions

Date:
November 19, 2021
Source:
Institute for Basic Science
Summary:
Nickel-cobalt metal dimer on nitrogen-doped carbon can catalyze
electrolysis under both acidic and basic conditions.



FULL STORY ==========================================================================
The limited reservoir of fossils fuels and the ever-increasing threats
of climate change have encouraged researchers to develop alternative technologies to produce eco-friendly fuels. Green hydrogen generated from
the electrolysis of water using renewable electricity is considered a next-generation renewable energy source for the future. But in reality,
the overwhelming majority of hydrogen fuel is obtained from the refining
of fossils 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 show
poor stability under long- term operation.

Recently, single-atom catalysts have shown excellent activity compared
to their nanomaterial-based counterparts. This is because they are able
to achieve up to 100% atom utilization, whereas in nanoparticles only the surface atoms are available for reaction. However, due to the simplicity
of the single-metal-atom center, carrying out further modification of
the catalysts to perform complex multistep reactions is rather difficult.

The simplest way to modify the single atoms is by turning them
into single-atom dimers, which combine two different single atoms
together. Tuning the active site of single-atom catalysts with dimers can improve the reaction kinetics thanks to the synergistic effect between
two different atoms. However, while the synthesis and identification
of the single-atom dimer structure have been known conceptually, its
practical realization has been very difficult.

This problem was tackled 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.

"We synthesized Ni-Co single atom dimer structure on nitrogen (N)-doped
carbon support via in-situ trapping of Ni/Co ions into the polydopamine
sphere, followed by pyrolysis with precisely controlled N-coordination. We employed state-of-the-art transmission electron microscopy and x-ray
absorption spectroscopy to successfully identify these NiCo-SAD sites
with atomic precision," says Ashwani Kumar, the first author of the study.

The researchers found that annealing for two hours at 800DEGC in an argon atmosphere was the best condition for obtaining the dimer 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 overpotential required to drive the hydrogen evolution reaction.

The NiCo-SAD-NC electrocatalyst had a comparable level of overvoltage as commercial Pt-based catalysts in acidic and alkaline media. NiCo-SAD-NC
also exhibited 8 times higher activity than Ni/Co single-atom catalysts
and heterogeneous NiCo nanoparticles in alkaline media. At the same time,
it achieved 17 and 11 times higher activity than Co and Ni single-atom catalysts, respectively, and 13 times higher than conventional Ni/Co nanoparticles in acidic media.

In addition, the researchers demonstrated the long-term stability of the
new catalyst, which was able to drive reaction for 50 hours without any
change of structure. The NiCo-SAD exhibited superior water dissociation
and optimal proton adsorption compared to other single-atom dimers and
Ni/Co single-atom sites, boosting pH-universal catalyst's activity based
on the density functional theory simulation.

"We were very excited to discover that the novel NiCo-SAD structure
dissociates water molecules with a much lower energy barrier and
accelerates hydrogen evolution reaction in both alkaline and acidic
media with performances comparable to that of Pt, which addressed the shortcomings of the individual Ni and Co single-atom catalysts. The
synthesis of such single atom dimer structure was a long-standing
challenge in the field of single-atom catalysts," notes Associate Director
Lee, the corresponding author of the study.

He further explains, "This study takes us a step closer to a carbon-free
and green hydrogen economy. This highly efficient and inexpensive
hydrogen generation electrocatalyst will help us overcome long-term
challenges of cost- competitive green hydrogen production: to produce high-purity hydrogen for commercial applications at a low price and in an eco-friendly manner." The study was published in Nature Communications(IF 14.92), a world-renowned journal in the field of basic science.

========================================================================== Story Source: Materials provided by Institute_for_Basic_Science. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ashwani Kumar, Viet Q. Bui, Jinsun Lee, Lingling Wang, Amol
R. Jadhav,
Xinghui Liu, Xiaodong Shao, Yang Liu, Jianmin Yu, Yosep Hwang,
Huong T.

D. Bui, Sara Ajmal, Min Gyu Kim, Seong-Gon Kim, Gyeong-Su Park,
Yoshiyuki Kawazoe, Hyoyoung Lee. Moving beyond bimetallic-alloy
to single-atom dimer atomic-interface for all-pH hydrogen
evolution. Nature Communications, 2021; 12 (1) DOI:
10.1038/s41467-021-27145-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211119085127.htm

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