Explore the vast range of titles available.

Single-atom catalysts (SACs) with M-N 4 structure have drawn significant attention due to the facile preparation, maximum atom efficiency, unique electronic properties, uniform active sites, and excellent activity. Such catalysts integrated the merits of traditional homogeneous and heterogeneous catalysts effectively solve the cost, activity, and reuse problems. More importantly, the M-N 4 structure is flexible and other species like atoms, groups, and particles can be added to precisely control the local environment of M-N 4 to further improve the catalytic performance. Although unprecedented progress has been made, it remains difficulties in the rational design and controllable synthesis of a suitable SAC for a certain application. This review introduces the progress of M-N 4 catalysts and summarizes the strategies to modulate the M-N 4 structure, including changing the coordination number, tailoring the coordination structure, coordinating with groups, creating dual-atom catalysts (DACs), and coexisting of SAC with DAC and cluster. Special emphasis is placed on the preparation, structure characterization, and reaction mechanism of M-N 4 -derived catalysts. Finally, the current challenges of these catalysts are also discussed to provide guidelines for the future design of efficient catalysts.

Owing to the rapidly increasing consumption of fossil fuels, finding clean and reliable new energy sources is of the utmost importance. Thus, developing highly efficient and low‐cost catalysts for electrochemical reactions in energy conversion devices is crucial. Single‐atom catalysts (SACs) with maximum metal atom utilization efficiency and superior catalytic performance have attracted significant attention, especially for electrochemical reactions. However, because of the highly unsaturated coordination environment, the stability of SACs can be a challenge for practical applications. In this review, we will summarize the strategies to increase the stability of SACs and synthesizing stable SACs, as well as the application of SACs in electrochemical reactions. Finally, we offer a perspective on the development of advanced SACs through rational design and a deeper understanding of SACs with the help of in situ or operando techniques in electrochemical reactions. This review provides the recent advances and strategies in the stabilization of single‐atom catalysts (SACs), including spatial confinement, proximity sites modification, strong metal ‐ support interactions, and electronic metal‐support interactions. The application and development of SACs in electrochemical reactions are summarized. Finally, a perspective toward the rational design and deeper understanding of advanced SACs are also offered.

Single‐atom catalysts (SACs) are attracting extensive attention due to their incredibly catalytic activity and selectivity, high utilization of metal atoms, and obvious cost reduction. The unique ordered porous materials (OPMs) are promising carriers for stabilizing single atoms due to their large surface areas and uniformly tunable pore sizes. Meantime, the geometric and electronic structures of single‐atom metals can be tuned by the interaction between the single‐atoms (SAs) and OPMs to enhance the catalytic activity of SACs. The SACs based on OPMs, such as zeolites, metal–organic frameworks, and ordered mesoporous materials, have been developing fast recently. Herein, we review recent advancements on structural feature, synthetic strategy, characterization technique, and catalytic applications of OPMs‐based SACs. The opportunities and challenges about SAs/OPMs are also provided to develop the novel catalysts with superior catalytic performances in the future. Ordered porous materials (OPMs)‐based single‐atom catalysts (SACs) with unique electronic state via a confinement effect have aroused extensive interest due to their large surface areas and uniformly tunable pore sizes. This review summarizes the recent development of OPMs‐based SACs in structures, synthetic methods, characterization technologies, and catalytic applications.

Converting CO2 emissions to valuable carbonaceous chemicals/fuels under mild conditions provides a sustainable way to maintain carbon balance and alleviate the energy shortage. Low‐dimensional material (LDM) supported single‐atom catalysts (SACs) have been attracted significant attention for electrochemical CO2 reduction reaction (ECR) in recent years. This is mainly because integrating the single‐atoms and LDMs can inherit the advantages of themselves and the synergy effects between them are potential to enhance the ECR performance. In this review, we summarized the strategies for synthesizing LDM supported SACs for ECR, and different LDM supported SACs for ECR have been briefly introduced. Moreover, some optimization strategies for LDM supported SACs towards CO2 electroreduction are highlighted. At the end of this review, the perspectives and challenges of LDM supported SACs for ECR are provided. In this review, we have systematically summarized the low‐dimensional material (LDM) supported single‐atom catalysts (SACs) for ECR, and the perspectives and challenges of LDM supported SACs for ECR are also provided.

Transition‐metal nitrogen‐doped carbons (TM‐N‐C) are emerging as a highly promising catalyst class for several important electrocatalytic processes, including the electrocatalytic CO2 reduction reaction (CO2RR). The unique local environment around the singly dispersed metal site in TM‐N‐C catalysts is likely to be responsible for their catalytic properties, which differ significantly from those of bulk or nanostructured catalysts. However, the identification of the actual working structure of the main active units in TM‐N‐C remains a challenging task due to the fluctional, dynamic nature of these catalysts, and scarcity of experimental techniques that could probe the structure of these materials under realistic working conditions. This issue is addressed in this work and the local atomistic and electronic structure of the metal site in a Co–N–C catalyst for CO2RR is investigated by employing time‐resolved operando X‐ray absorption spectroscopy (XAS) combined with advanced data analysis techniques. This multi‐step approach, based on principal component analysis, spectral decomposition and supervised machine learning methods, allows the contributions of several co‐existing species in the working Co–N–C catalysts to be decoupled, and their XAS spectra deciphered, paving the way for understanding the CO2RR mechanisms in the Co–N–C catalysts, and further optimization of this class of electrocatalytic systems. Operando XANES analysis assisted by machine learning, spectral decomposition approaches and DFT modelling is employed to shed light on the speciation of Co and N co‐doped carbon catalyst during electrocatalytic CO2 conversion.

The concept of “green‐ammonia‐zero‐carbon emission” is an emerging research topic in the global community and many countries driving toward decarbonizing a diversity of applications dependent on fossil fuels. In light of this, electrochemical nitrogen reduction reaction (ENRR) received great attention at ambient conditions. The low efficiency (%) and ammonia (NH3) production rates are two major challenges in making a sustainable future. Besides, hydrogen evolution reaction is another crucial factor for realizing this NH3 synthesis to meet the large‐scale commercial demand. Herein, the (i) importance of NH3 as an energy carrier for the next future, (ii) discussion with ENRR theory and the fundamental mechanism, (iii) device configuration and types of electrolytic systems for NH3 synthesis including key metrics, (iv) then moving into rising electrocatalysts for ENRR such as single‐atom catalysts (SACs), MXenes, and metal–organic frameworks that were scientifically summarized, and (v) finally, the current technical contests and future perceptions are discussed. Hence, this review aims to give insightful direction and a fresh motivation toward ENRR and the development of advanced electrocatalysts in terms of cost, efficiency, and technologically large scale for the synthesis of green NH3. This review aims to give insightful direction and a fresh motivation toward the electrochemical synthesis of ammonia via nitrogen reduction reaction (ENRR). We proposed emerging electrocatalysts toward ENRR such as single‐atom catalysts, MXenes, and metal–organic frameworks for the synthesis of green ammonia.

Efficient n = O bond activation is crucial for the catalytic reduction of nitrogen compounds, which is highly affected by the construction of active centers. In this study, n = O bond activation was achieved by a single-atom catalyst (SAC) with phosphorus anchored on a Co active center to form intermediate N-species for further hydrogenation and reduction. Unique phosphorus-doped discontinuous active sites exhibit better n = O activation performance than conventional N-cooperated single-atom sites, with a high Faradic efficiency of 92.0% and a maximum ammonia yield rate of 433.3 μg NH4·h−1 cm−2. This approach of constructing environmental sites through heteroatom modification significantly improves atom efficiency and will guide the design of future functional SACs with wide-ranging applications.

Electrochemical CO2 reduction reaction (CO2RR) to produce value‐added products has received tremendous research attention in recent years. With research efforts across the globe, remarkable advancement has been achieved, including the improvement of selectivity for the reduction products, the realization of efficient reduction beyond two electrons, and the delivery of industrially relevant current densities. In this review, we introduce the recent development of nanomaterials for CO2RR, including the zero‐dimensional graphene quantum dots, two‐dimensional materials such as metal chalcogenides and metal/covalent organic framework, single‐atom catalysts, and nanostructured metal catalysts. The engineering of materials into three‐dimensional structure will also be discussed. Finally, we will provide a summary of the catalytic performance and perspectives on future development. Here, we review the recent development of nanostructured materials for CO2 reduction reaction, including the graphene quantum dots, metal chalcogenides, porous organic materials, single‐atom catalysts, nanostructured metals, and their structural engineering into three‐dimension skeletons.

As a carbon‐free energy carrier, hydrogen has become the pivot for future clean energy, while efficient hydrogen production and combustion still require precious metal‐based catalysts. Single‐atom catalysts (SACs) with high atomic utilization open up a desirable perspective for the scale applications of precious metals, but the general and facile preparation of various precious metal‐based SACs remains challenging. Herein, a general movable printing method has been developed to synthesize various precious metal‐based SACs, such as Pd, Pt, Rh, Ir, and Ru, and the features of highly dispersed single atoms with nitrogen coordination have been identified by comprehensive characterizations. More importantly, the synthesized Pt‐ and Ru‐based SACs exhibit much higher activities than their corresponding nanoparticle counterparts for hydrogen oxidation reaction and hydrogen evolution reaction (HER). In addition, the Pd‐based SAC delivers an excellent activity for photocatalytic hydrogen evolution. Especially for the superior mass activity of Ru‐based SACs toward HER, density functional theory calculations confirmed that the adsorption of the hydrogen atom has a significant effect on the spin state and electronic structure of the catalysts. A facile movable type printing method is developed to synthesize precious metal‐based single‐atom catalysts, where C3N4 and nitrogen‐doping carbon derived from melamine and polydopamine are used as template and support, respectively. These precious metal‐based single‐atom catalysts can present efficient catalytic activity toward various hydrogen reactions containing hydrogen evolution reaction, photocatalytic hydrogen evolution, and hydrogen oxidation reaction.

Single‐atom catalysts (SACs) are regarded as promising electrocatalysts for various reactions in the field of energy conversion and storage owing to their maximized atom utilization efficiency and unique electronic properties. The modifications of local coordination structures of single metal centers play significant roles in dominating catalytic performances, thus the SACs are resurveyed with different local coordination environments in order to explore such a paramount structure–performance relationship in various energy‐conversion reactions, including O2/CO2 reduction reaction and hydrogen evolution reaction. Notably, the atomically dispersed metal atoms that are subject to working conditions will undergo dynamic changes and then affect the catalytic properties, consequently, understanding the dynamic nature of SACs during reactions is highly significant but is still lacking to date. To this endeavor, this review particularly summarizes the dynamic evolutions of local coordination structures of SACs in various electrochemical reactions based on advanced operando/in situ techniques, aiming to precisely demonstrate the correlation between the dynamic coordination environment of SACs and the electrocatalytic activity. Finally, the challenges and perspectives are highlighted in the mechanistic studying for understanding the accurate active sites of SACs under realistic working conditions. Single‐atom catalysts (SACs) will undergo dynamic changes and then affect the catalytic properties under working conditions; consequently, understanding the dynamic nature of SACs during reactions is highly significant. Hence, this review particularly summarizes the dynamic evolutions of local coordination structures of SACs in electrocatalytic reactions, aiming to demonstrate such dynamic coordination environment ‐ electrocatalytic activity relationship.