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1. Dual‐Atom Catalysts for Electrochemical Energy Technologies

   https://doi.org/10.1002/ente.202201456  

   Cui, Tianchen; Liu, Qiming; Chen, Shaowei (February 2023, Energy Technology)

   Rational design and engineering of high‐performance, low‐cost electrocatalysts represents a critical first step in the development of sustainable energy technologies. While single‐atom catalysts (SACs) have emerged as viable candidates, recent research has shown that the structure and activity can be further manipulated and enhanced by the incorporation of a second metal center in the close proximity, forming a binuclear configuration. Such dual‐atom catalysts (DACs) are recognized as feasible choices to break the limitations of SACs due to the synergetic effects between the bimetallic atoms and their special structures. Herein, the recent advances of DAC electrocatalysis for a range of important reactions, focusing on their synthesis, characterization, and performance, are summarized. The review is concluded with a perspective highlighting the challenges and future research directions. 

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2. Pt ₁ –O ₄ as active sites boosting CO oxidation via a non-classical Mars–van Krevelen mechanism

   https://doi.org/10.1039/D1CY00115A  

   Lou, Yang; Zheng, Yongping; Guo, Wenyi; Liu, Jingyue (May 2021, Catalysis Science & Technology)

   null (Ed.)

   Single-atom catalysts (SACs) exhibit excellent performance for various catalytic reactions but it is still challenging to have adequate total activity for practical applications. Here we report the high-valence, square planar Pt 1 –O 4 as an active site that enables significantly to increase the total activity of the Pt 1 /Fe 2 O 3 SAC with a Pt loading of only ∼30 ppm, which is similar to that of a 1.0 wt% nano-Pt/Fe 2 O 3 , for CO oxidation at 350 °C. Density functional theory calculations reveal that Pt 1 –O 4 catalyzes CO oxidation through a non-classical Mars–van Krevelen mechanism. The adsorbed O 2 on Pt 1 atoms activates the coordination oxygen in the Pt 1 –O 4 configuration, and then a barrierless O 2 dissociation occurs on the Pt 1 –Fe 2 triangle to replenish the consumed coordination oxygen by the cooperative action of Pt 5d and Fe 3d electrons. This work provides a new fundamental understanding of oxidation catalysis on stable and active SACs, providing guidance for rationally designing future heterogeneous catalysts. 

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3. Computational Screening of Efficient Single‐Atom Catalysts Based on Graphitic Carbon Nitride (g‐C ₃ N ₄ ) for Nitrogen Electroreduction

   https://doi.org/10.1002/smtd.201800368  

   Chen, Zhe; Zhao, Jingxiang; Cabrera, Carlos R.; Chen, Zhongfang (December 2018, Small Methods)

   Abstract The development of low‐cost and efficient electrocatalysts for nitrogen reduction reaction (NRR) at ambient conditions is crucial for NH₃synthesis and provides an alternative to the traditional Harber‐Bosch process. Herein, by means of density functional theory (DFT) computations, the catalytic performance of a series of single metal atoms supported on graphitic carbon nitride (g‐C₃N₄) for NRR is evaluated. Among all the candidates, the Gibbs free energy change of the potential‐determining step for five single‐atom catalysts (SACs), namely Ti, Co, Mo, W, and Pt atoms supported on g‐C₃N₄monolayer, is lower than that on the Ru(0001) stepped surface. In particular, the single tungsten (W) atom anchored on g‐C₃N₄(W@g‐C₃N₄) exhibits the highest catalytic activity toward NRR with a limiting potential of −0.35 V via associative enzymatic pathway, and can well suppress the competing hydrogen evolution reaction. The high NRR activity and selectivity of W@g‐C₃N₄are attributed to its inherent properties, such as significant positive charge and large spin moment on the W atom, excellent electrical conductivity, and moderate adsorption strength with NRR intermediates. This work opens up a new avenue of N₂reduction for renewable energy supplies and helps guide future development of single‐atom catalysts for NRR and other related electrochemical process. 

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4. Directly Predicting Limiting Potentials from Easily Obtainable Physical Properties of Graphene-Supported Single-Atom Electrocatalysts by Machine Learning

   https://doi.org/10.1039/C9TA13404B  

   Lin, Shiru; Xu, Haoxiang; Wang, Yekun; Zeng, Xiao Cheng; Chen, Zhongfang (January 2020, Journal of Materials Chemistry A)

   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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5. Altering Ligand Fields in Single-Atom Sites through Second-Shell Anion Modulation Boosts the Oxygen Reduction Reaction

   https://doi.org/10.1021/jacs.1c11331  

   Qin, Jiayi; Liu, Hui; Zou, Peichao; Zhang, Rui; Wang, Chunyang; Xin, Huolin L. (January 2022, Journal of the American Chemical Society)

   Single-atom catalysts based on metal–N4 moieties and anchored on carbon supports (defined as M–N–C) are promising for oxygen reduction reaction (ORR). Among those, M–N–C catalysts with 4d and 5d transition metal (TM4d,5d) centers are much more durable and not susceptible to the undesirable Fenton reaction, especially compared with 3d transition metal based ones. However, the ORR activity of these TM4d,5d–N–C catalysts is still far from satisfactory; thus far, there are few discussions about how to accurately tune the ligand fields of single-atom TM4d,5d sites in order to improve their catalytic properties. Herein, we leverage single-atom Ru–N–C as a model system and report an S-anion coordination strategy to modulate the catalyst’s structure and ORR performance. The S anions are identified to bond with N atoms in the second coordination shell of Ru centers, which allows us to manipulate the electronic configuration of central Ru sites. The S-anion-coordinated Ru–N–C catalyst delivers not only promising ORR activity but also outstanding long-term durability, superior to those of commercial Pt/C and most of the near-term single-atom catalysts. DFT calculations reveal that the high ORR activity is attributed to the lower adsorption energy of ORR intermediates at Ru sites. Metal–air batteries using this catalyst in the cathode side also exhibit fast kinetics and excellent stability. 

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