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Oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are three critical reactions for energy-related applications, such as water electrolyzers and metal-air batteries. Graphene-supported single-atom catalysts (SACs) have been widely explored; however, either experiments or density functional theory (DFT) computations cannot screen catalysts at high speed. Herein, based on DFT computations of 104 graphene-supported SACs (M@C3, M@C4, M@pyridine-N4, and M@pyrrole-N4), we built up machine learning (ML) models to describe the underlying pattern of easily obtainable physical properties and limiting potentials (errors = 0.013/0.005/0.020 V for ORR/OER/HER, respectively), and employed these models to predict the catalysis performance of 260 other graphene-supported SACs containing metal-NxCy active sites (M@NxCy). We recomputed the top catalysts recommended by ML towards ORR/OER/HER by DFT, which confirmed the reliability of our ML model, and identified two OER catalysts (Ir@pyridine-N3C1 and Ir@pyridine-N2C2) outperforming noble metal oxides, RuO2 and IrO2. The ML models quantitatively unveiled the significance of various descriptors and fast narrowed down the potential list of graphene-supported single-atom catalysts. This approach can be easily used to screen and design other SACs, and significantly accelerate the catalyst design for many other important reactions.
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Single atom electrocatalysts supported on graphene or graphene-like carbons
Electrocatalysis plays an essential role in diverse electrochemical energy conversion processes that are vital for improving energy utilization efficiency and mitigating the aggravating global warming challenge. The noble metals such as platinum are generally the most frequently used electrocatalysts to drive these reactions and facilitate the relevant energy conversion processes. The high cost and scarcity of these materials pose a serious challenge for the wide-spread adoption and the sustainability of these technologies in the long run, which have motivated considerable efforts in searching for alternative electrocatalysts with reduced loading of precious metals or based entirely on earth-abundant metals. Of particular interest are graphene-supported single atom catalysts (G-SACs) that integrate the merits of heterogeneous catalysts and homogeneous catalysts, such as high activity, selectivity, stability, maximized atom utilization efficiency and easy separation from reactants/products. The graphene support features a large surface area, high conductivity and excellent (electro)-chemical stability, making it a highly attractive substrate for supporting single atom electrocatalysts for various electrochemical energy conversion processes. In this review, we highlight the recent advancements in G-SACs for electrochemical energy conversion, from the synthetic strategies and identification of the atomistic structure to electrocatalytic applications in a variety of reactions, and finally conclude with a brief prospect on future challenges and opportunities.
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- Award ID(s):
- 1800580
- PAR ID:
- 10204908
- Date Published:
- Journal Name:
- Chemical Society Reviews
- Volume:
- 48
- Issue:
- 20
- ISSN:
- 0306-0012
- Page Range / eLocation ID:
- 5207 to 5241
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Atomic dispersion of metal catalysts on a substrate accounts for the increased atomic efficiency of single-atom catalysts (SACs) in various catalytic schemes compared to the nanoparticle counterparts. However, lacking neighboring metal sites has been shown to deteriorate the catalytic performance of SACs in a few industrially important reactions, such as dehalogenation, CO oxidation, and hydrogenation. Metal ensemble catalysts (M n ), an extended concept to SACs, have emerged as a promising alternative to overcome such limitation. Inspired by the fact that the performance of fully isolated SACs can be enhanced by tailoring their coordination environment (CE), we here evaluate whether the CE of M n can also be manipulated in order to enhance their catalytic activity. We synthesized a set of Pd ensembles (Pd n ) on doped graphene supports (Pd n /X-graphene where X = O, S, B, and N). We found that introducing S and N onto oxidized graphene modifies the first shell of Pd n converting Pd–O to Pd–S and Pd–N, respectively. We further found that the B dopant significantly affected the electronic structure of Pd n by serving as an electron donor in the second shell. We examined the performance of Pd n /X-graphene toward selective reductive catalysis, such as bromate reduction, brominated organic hydrogenation, and aqueous-phase CO 2 reduction. We observed that Pd n /N-graphene exhibited superior performance by lowering the activation energy of the rate-limiting step, i.e., H 2 dissociation into atomic hydrogen. The results collectively suggest controlling the CE of SACs in an ensemble configuration is a viable strategy to optimize and enhance their catalytic performance.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1039/C9CS00422J
