Atomically-thin two-dimensional sheets for understanding active sites in catalysis

Abstract

Catalysis can speed up chemical reactions and it usually occurs on the low coordinated steps, edges, terraces, kinks and corner atoms that are often called "active sites". However, the atomic level interplay between active sites and catalytic activity is still an open question, owing to the large difference between idealized models and real catalysts. This stimulates us to pursue a suitable material model for studying the active sites-catalytic activity relationship, in which the atomically-thin two-dimensional sheets could serve as an ideal model, owing to their relatively simple type of active site and the ultrahigh fraction of active sites that are comparable to the overall atoms. In this tutorial review, we focus on the recent progress in disclosing the factors that affect the activity of reactive sites, including characterization of atomic coordination number, structural defects and disorder in ultrathin two-dimensional sheets by X-ray absorption fine structure spectroscopy, positron annihilation spectroscopy, electron spin resonance and high resolution transmission electron microscopy. Also, we overview their applications in CO catalytic oxidation, photocatalytic water splitting, electrocatalytic oxygen and hydrogen evolution reactions, and hence highlight the atomic level interplay among coordination number, structural defects/disorder, active sites and catalytic activity in the two-dimensional sheets with atomic thickness. Finally, we also present the major challenges and opportunities regarding the role of active sites in catalysis. We believe that this review provides critical insights for understanding the catalysis and hence helps to develop new catalysts with high catalytic activity.

A highly-efficient oxygen evolution electrode based on defective nickel-iron layered double hydroxide

“…2d) was carried out to confirm the defect structure of R-NiFe LDH. While the EPR signal of P-NiFe LDH was relatively weak (due to the very limited defects), a broad and strong signal of R-NiFe LDH was detected, demonstrating a defect-rich structure [37]. Moreover, the signals of RNiFe LDH at g = 1.99 could be identified as the electrons trapped on oxygen vacancies, indicating the defects in RNiFe LDH were oxygen vacancies [38].…”

Single‐Atom to Single‐Atom Grafting of Pt1 onto FeN4 Center: Pt1@FeNC Multifunctional Electrocatalyst with Significantly Enhanced Properties

“…[23,45] The other is associated with the low coordinated dangling Pt 4+ atoms that may facilitate the H 2 O adsorption and promote OER, although metallic Pt NPs are not active to OER. [22,46] In addition, the overvoltage (ΔE = E j = 10 −E 1/2 ) between OER and ORR, which is used to evaluate the reversibility of oxygen electrodes, is 0.67 V for Pt 1 @FeNC, much lower than that of the recently reported highly active NPMCs, precious metal, and metal-free catalysts, e.g., Co@Co 3 O 4 / NC (0.85 V), [47] Fe@N-C-700 (0.88 V), [48] 20 wt% PtRu/C (0.88 V), [49] S-doped CNTs (0.79 V). [50] The superior ORR/OER bifunction of Pt 1 @FeNC raises its potential application in regenerative fuel cell, which combine the fuel cell and water splitting in one device.…”

“…Defects, low coordination atoms, and dangling bonds on catalysts are usually important active sites for OER/HER. [22] The synergy between hetero-components or -structures has also been proved as the key factor for high OER/HER activities. [23] Recently, the single-atom catalysts (SACs) have attracted much attention for electrocatalysis applications because of their unique properties such as the maximized atom utilization, high catalytic activity, and selectivity.…”

Two-Dimensional Material Molybdenum Disulfides as Electrocatalysts for Hydrogen Evolution

“…Several review papers have summarized the structure, synthesis, and composites of 2D TMDs, as well as their application in HER [16][17][18][19][20][21]. It is commonly accepted that unique 2D plenary structures provide ultrahigh specific surface area, atomic thickness, and an atomically flat facet [22]. Thus for the 2D TMDs, it is not only easy to achieve high catalytic activity, but also to modify the chemical and physical properties so as to further improve their catalytic performance [23].…”