Atomically Precise Electrocatalysts for Electrochemical Energy Applications

Atomically precise nanoclusters (APN) are more useful for detecting the reaction mechanisms and active sites of the electrocatalysis process at the molecular or atomic level. The atomically precise metal nanoclusters are used as efficient catalysts in most electrocatalytic reactions, including hydrogen evolution reactions, electrochemical CO₂ reduction reactions, fuel cell reactions, degradation reactions of contaminants, and electrochemical synthesis of ammonia. The various factors influencing the electrocatalytic properties of metal nanoclusters include the core, charge of the metal, metal atom distribution, kinds of protection ligands, substrates, and the detailed structure of the metal nanoclusters. The design of fuel cells is challenging because of the formulation and design of effective electrocatalysts for the slow cathodic oxygen reduction reaction (ORR). Amongst the differently designed electrocatalysts, presently the atomically precise electrocatalysts (APE), like single-atom, multi-atom, and dual-atom clusters, have been emphasized by researchers because of their outstanding effectiveness in atom utilization and catalytic performance. The nanoparticle of metal now captures a vital position in the catalytic activity of electrocatalysis. Therefore, APN shows the properties of metal nanoclusters passivated by ligands and is today considered an effective class of model catalyst that provides great potential in the field of catalysis research.

A possible strategy is to create electrochemical methods of conversion that may utilize renewable energy to transform airborne molecules like water, nitrogen, and carbon dioxide into commodities with value added. Due to their ability to influence the rate, effectiveness, and specificity of chemical transformation responses, electrocatalysts serve a vital part in these processes. The generation of energy that is environmentally friendly relies heavily on electrochemical energy transformations. Nevertheless, the outcome falls short of expectations since there are no highly effective and reliable electrocatalysts. Because of their high operation, stability, and potential to maximize utilization effectiveness, single, dual, and multi-atom catalysts have recently become hot study subjects in the field of electrocatalysis. The synthesis, characterization, and computer modeling of nanoscale materials have seen ongoing advancements. Hence the present book chapter discusses the important electrocatalytic applications of atomically precise Single/Dual/Multi-atom catalysts toward electrochemical energy applications. We expect that this chapter can offer perspectives for logical planning and effective formulation of improved electrocatalysts with atomic precision by examining structure–activity/stability correlations and electrochemical processes of diverse atomically precise electrocatalysts.

This comprehensive review explores recent electrochemical energy conversion and storage advancements, focusing on revolutionary catalyst strategies. The discussion covers single-atom catalysts, emphasizing their applications and unique advantages. Metal–Organic frameworks (MOFs) are then examined for their potential in creating single-atom catalysts through various approaches. The exploration extends to dual-atom catalysts, highlighting their distinct attributes, followed by an investigation into binuclear homolog/heterolog dual-metal atom pairs and their contributions. The review concludes by emphasizing the innovative synthesis of MOF-derived metal clusters and their significant implications in energy conversion and storage. Overall, this multifaceted review provides insights into cutting-edge electrochemical catalyst strategies, foreseeing a promising future for energy conversion and storage technologies.

A well-defined model nanocatalyst is absolutely necessary to reveal the detailed mechanism of electro-catalysis and thereby to lead to the development of a new efficient electro-catalyst. Atomically regulated metal nanoclusters will allow us to systematically optimize the electrochemical and surface properties suitable for electro-catalysis, giving a potent platform for precisely tuned electro-catalysis. Nanoclusters are made up of metal atoms and ligands with diameters ranging from 2 to 3 nm. Gold nanoclusters with precise atomic numbers have received a lot of attention due to their stability and unusual structure. More new ways for synthesizing atomically accurate gold nanoclusters have been developed as a result of more extensive research on gold nanoclusters. Recent advances in the electrochemistry of atomically accurate metal nanoclusters and their applications in electro-catalysis are discussed in this account. Other metal nanoclusters have made far less progress in electrochemical investigations than gold nanoclusters; hence, this chapter focuses on electro-catalyst applications of metal-based nanoclusters. Voltammetry has proven to be particularly effective in studying the electrical structure of metal nanoclusters.

Electrochemical energy conversion and storage (EECS) technologies have aroused worldwide interest as a consequence of the rising demands for renewable and clean energy. As a sustainable and clean technology, EECS has been among the most valuable options for meeting increasing energy requirements and carbon neutralization. Consequently, EECS technologies with high energy and power density were introduced to manage prevailing energy needs and ecological issues. In this contribution, recent trends and strategies on EECS technologies regarding devices and materials have been reviewed. The main features of EECS strategies; conventional, novel, and unconventional approaches; integration to develop multifunctional energy storage devices and integration at the level of materials; modeling and optimization of EECS technologies; EECS materials and devices along with challenges and limitations have been reviewed. Finally, conclusions and perspectives concerning upcoming studies were outlined for a better understanding of innovative approaches for the future development of high-performance EECS devices. It has been highlighted that electrochemical energy storage (EES) technologies should reveal compatibility, durability, accessibility and sustainability. Energy devices must meet safety, efficiency, lifetime, high energy density and power density requirements. Their competitiveness regarding performance, material and device stability, costs, and sustainability remains to be further improved.

The study of electrocatalysts for oxygen evolution reaction (OER) in water electrolysis is a rapidly advancing field, often utilizing noble metal-based materials. The chapter begins with an introduction to water electrolysis and then a current understanding of the two half-cell reactions, namely the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with a focus on their reaction mechanisms in both alkaline and acidic media. This chapter offers a comprehensive overview of fundamental knowledge related to the use of catalysts for the OER in water electrolysis. The discussion covers various categories of catalysts, including noble metals-based catalysts, transition metals-based catalysts, carbon nanotube-based metal/metal oxides catalysts, carbon nanotube-based metal-free electrocatalysts, and perovskite oxides electrocatalysts.

The principles of the oxygen reduction reaction (ORR), including electrocatalysts and kinetics, are covered in this chapter. Based on the literature, both experimental and theoretical methods are used to explore the ORR kinetics, including reaction processes catalyzed by various electrode materials and catalysts, such as Pt-based alloys, carbon materials, and transition metal macrocyclic complexes. It was emphasized that although there is a large literature on ORR, there is still a need to design materials that can compete with noble metal-containing catalysts for ORR.

The quest for sustainable energy solutions has propelled the field of electrocatalysis into the spotlight, with a particular focus on the development of high-performance oxygen reduction reaction (ORR) electrocatalysts. In this dynamic landscape, single-atom catalysts (SACs) emerge as frontrunners, celebrated for their remarkable electrocatalytic prowess and the efficient utilization of individual atoms. However, like any trailblazing technology, SACs encounter a formidable challenge—their elevated surface energy poses a hurdle, leading to a restricted loading of metal atoms. This limitation, in turn, curtails their practical viability. This chapter serves as a panoramic exploration of the progress achieved in the extensive realm of SACs research, offering a nuanced understanding of the various facets of ORR electrocatalysts. From the distinguished noble metal SACs, known for their intrinsic excellence, to the versatile transition metal SACs, each category unfolds a unique narrative of breakthroughs and innovations. Additionally, the exploration extends to the realm of double metal SACs, delving into the synergies that arise when combining different metal species. By providing a comprehensive overview, this chapter not only encapsulates the current state of SACs research but also lays the foundation for future endeavors in harnessing sustainable energy through cutting-edge electrocatalytic technologies.

Electrochemical energy applications, such as fuel cells and metal-air batteries, rely on efficient oxygen reduction reactions (ORR) to convert chemical energy into electrical energy. Atomically precise ORR electrocatalysts have recently emerged as promising candidates for enhancing the performance of these devices due to their precise atomic structures and unique catalytic properties. However, the design and optimization of these electrocatalysts require a comprehensive understanding of their activity descriptors. This chapter provides an overview of the activity descriptors for atomically precise ORR electrocatalysts and their implications for electrochemical energy applications. It covers the synthesis methods for atomically precise catalysts, the ORR mechanisms on these catalysts, and the various activity descriptors that influence their performance. The chapter also discusses computational approaches, such as density functional theory (DFT) calculations and machine learning, employed to study these activity descriptors. Furthermore, the implications of activity descriptors for electrochemical energy applications, including fuel cells and metal-air batteries, are explored. The challenges and future perspectives in this field are also discussed. This chapter serves as a comprehensive guide for researchers and scientists working in the field of electrocatalysis, providing valuable insights into the design and optimization of atomically precise ORR electrocatalysts for efficient energy conversion in electrochemical devices.

In the electrochemical process, the oxygen evolution reaction (OER) plays a crucial role by providing protons and electrons for cathodic reactions such as the hydrogen evolution reaction (HER) or carbon dioxide reduction reaction (CO₂RR). Since OER is the bottleneck of the electrochemical processes, it requires an active and durable catalyst that can generate high OER current density at minimum overpotential. In this context, single-atom catalysts (SACs) hold great promise for achieving significant catalytic mass activity by precisely utilizing metal active sites at the atomic level. However, SACs face a challenge where smaller particles tend to aggregate into clusters or larger particles due to their high surface energy. Consequently, it becomes imperative to gain a comprehensive understanding of the role of support materials, their interactions with SACs, and the behavior of SACs under OER conditions. This book chapter is dedicated to an exploration of recent advancements in the application of SACs for the OER. It encompasses a thorough examination of the structural characterization of SACs and delves into the utilization of in situ/operando spectroscopic techniques and computational research to uncover the underlying mechanisms responsible for their catalytic activity. Furthermore, the chapter provides a comprehensive summary of the OER catalytic activity and the stability of SACs, offering valuable insights into the current state of SAC technology.

The development of effective, low-cost, as well as stable electrocatalysts for water splitting to utilize hydrogen fuels is a serious issue. A potential technique which includes mixing diverse materials to create a synergistic impact, which has shown to be a distinctive and appealing concept. The oxygen evolution reaction (OER) plays an important role in numerous electrochemical devices in the context of electrochemical water splitting; however, it has sluggish kinetics. Multi-atom catalysts have various benefits, such as high intrinsic electrocatalytic activity, maximal atomic efficiency, diversified chemical characteristics, and positive atom-to-atom synergy. As a result, multi-atom catalysts (MACs) have received a lot of interest as enhanced electrocatalysts for OER. This chapter presents an in-depth overview of the most recent developments in MACs for OER electrocatalysis. The inherent benefits of MACs are fully examined first, with a focus on three hypothesized processes that emphasize the electrical structure of active sites. The structural activity using experimental results has been thoroughly investigated, which provide a framework for rational structural design. In addition, the current synthesis techniques and a thorough performance comparison are described. Finally, many avenues for enhanced MACs development for OER electrocatalysis are presented.

Oxygen evolution reaction (OER) is a chemical reaction in the process of generating molecular oxygen in the oxidation of water during oxygenic photosynthesis, electrolysis of water into oxygen and hydrogen, and electrocatalytic oxygen evolution from oxides and oxoacids. Noble metal oxides such as ruthenium and iridium oxides have good electrocatalytic activity for the OER process, but they have disadvantages such as high cost, inaccessibility, limited reserves, and durability. Therefore, the design and preparation of a low-cost, highly active, and high stable performance catalyst is necessary. In this regard, dual-atom catalysts (DACs) are a suitable option according to their characterization such as good electrocatalytic activity, high atomic efficiency, and synergic effects. Their atomically dispersed active sites lead to maximum utilization efficiency of the metal sites. This chapter presents an outlook on the design, catalytic mechanism, and application of dual-atom catalysts in oxygen evolution reactions.

Since the oxygen is in a triplet state and the oxygen evolution reaction (OER) mechanism is related to the electron spin state, it is possible to improve the catalytic ability by regulating the spin state of the catalyst. From this point of view, we first introduce the unique electronic structure of oxygen, oxygen evolution reaction products, and then detail the mechanism of electron spin correlation in the entire oxygen evolution reaction, and how the catalyst affects this electron spin state, thereby affecting the catalytic reaction rate. Then, we introduced the research on the regulation of the electron spin states of the catalyst. Since the research dimension of the electron spin states is mostly concentrated at the atomic level, the unique atomic structure of the single-atom catalyst is more conducive to the first research. Therefore, we introduced the research on the spin state regulation of the single-atom catalyst. The spin state control at the atomic level of catalysts such as spinel is further introduced. Finally, the research on spin state regulation of oxygen evolution catalysts was summarized and prospected. In the future, the mechanism of spin state regulation of catalysts at the atomic level should be studied more clearly by developing in situ characterization techniques.

In electrochemistry, the hydrogen evolution reaction (HER) ranks among the most significant reactions. HER is the easiest method to produce very pure hydrogen so the development of effective HER catalysts is of great importance. This situation has significantly influenced many researchers in the field of electrochemistry and made it the focus of active studies. In this direction, many catalysts with different structures have been developed for HER over many years. Among the various HER catalysts, atomically precise electrocatalysts (single-atom, dual-atom, and multi-atom) are becoming more popular because of their efficient use of atoms and impressive electrocatalytic performance. Recently, researchers have made significant efforts to synthesize and develop atomically precise HER catalysts with high activity and stability. However, it is critical to descriptor new strategies to improve catalytic activity. Therefore, different descriptors have been developed to describe the correlation between catalyst morphology and activity. In this chapter, we summarized the activity descriptors commonly used in the design of atomically precise HER catalysts and their importance. We also discussed their impact on performance. Finally, strategies developed to identify new descriptors for promising HER catalysts are proposed.

Single-atom catalysts (SACs) have sparked rapidly emerging research interest in industrial water-splitting electrolysis for sustainable hydrogen production. Downsizing the metal nanoparticles to SACs anchored on solid support reveals extraordinary reaction kinetics compared to bulk counterparts due to the distinct merits of atomically monodispersed catalytically active sites, tunable coordination environment, and greater atom utilization. Moreover, strong metal-support bonding favors swift charge transfer at the interface, which modulates the electronic structure towards remarkable and unique catalytic activity. In this regard, consistent efforts have been devoted to designing low-cost, durable, and highly effective SACs for hydrogen evolution reaction (HER). In this chapter, we present different innovative synthesis routes and focus on a combination of analytical characterization techniques to highlight the successful synthesis and determine the optimal SAC concentration, vital for high HER efficiency. Further, we elaborate on recent advancements and electrochemical characteristics of SACs towards HER applications. After this, we aim to provide a comprehensive understanding and in-depth analysis of electronic structure transformation and subsequent increase in a number of accessible surface active HER sites upon SAC introduction. Finally, current key challenges in SACs are briefly addressed and future outlooks for developing intriguing SACs for exceptionally high activity and stability are proposed.

Hydrogen (H₂) has recently gained considerable interest as a promising alternative to fossil fuels, presenting a clean and sustainable energy source. However, achieving the cost-effective production of hydrogen at a commercial scale is still challenging. The electrocatalytic hydrogen evolution reaction (HER) has great potential as a means for achieving efficient hydrogen production, where the electrocatalysis process plays a vital role. Regarding this, the development of cost-effective, active, and stable electrocatalysts that can enhance the reaction kinetics and reduce the overpotential required for HER, is essential to make the process practical. Recently, dual-atom catalysts (DACs), which are an extension of single-atom catalysts (SACs), have garnered significant attention. Compared to SACs, DACs offer advantages such as higher metal loadings and greater flexibility of active sites. This chapter aims to offer insights into the recent developments in DACs. It provides an overview of the existing methods used to synthesize DACs. Furthermore, it delves into the various techniques employed to characterize DACs. This encompasses aspects like electronic structure, local coordination, and geometric configuration of bimetallic dimers. The chapter also provides a summary of the electrocatalytic application of DACs for HER. Finally, it outlines potential future research directions for the advancement of DACs in HER application.

Electrochemical water splitting plays a crucial role in hydrogen production. Developing efficient electrocatalysts for the hydrogen evolution reaction (HER) is essential for advancing the electrolysis water industry. Multi-atom catalysts (MACs), which are composed of three or more atoms elements, have attracted enormous interest, due to their flexible compositional tunability and synergistic effects between multiple atoms. In this chapter, a systematical review was conducted on the research progress of MACs as efficient HER electrocatalysts. First, the scope and significance of MACs was defined. Then, three typical MACs for HER, including multi-atom alloys, multi-atom compounds, and multi-atom composites, were briefly discussed, in which the underlying mechanisms of the improved HER activities of these MACs were stressed. Through the analysis of the challenges and prospects, it is expected that these research advances could bring about some new insights on the MACs in catalytic performance enhancement and clean energy technology innovation, and this could offer some inspiration on the rational design of the MACs in energy electrocatalysis fields.

The optimized solution to growing problems interconnected with rising energy demands and the environment is the development of renewable energy-storage devices. Among the multiple energy storage devices, the most demanding option is the batteries due to their huge energy density and specific capacity, abundant raw materials, remarkable cycling efficiency, paramount energy efficacy, wide temperature range, and smooth performance during the charge–discharge process. The development of appropriately designed electrode materials to meet the required threshold is an area of future concern for the researchers. Metal–organic frameworks (MOFs) display excellent electrochemical responses due to their tunable porosity, flexibility, conductivity, easy functionalization, and huge specific surface area. These silent features makes them a captivating electrode material with exceptional electrochemical behavior for the presently dominated lithium-ion batteries. Henceforth, this review recaps the recent advancements in MOFs-based electrode materials for high-performance Li-ion batteries. This review concisely describe the evolution of batteries, the basic principle and mechanism of Li-ion batteries, and explicate the recent advances in MOFs, MOF-derived materials, and MOFs composites as an electrode material for Li-ion batteries along with their electrochemical response.  Furthermore, the future prospects of MOFs-based materials for Li-ion batteries are outlined.

Metal-air batteries have been extensively considered owing to their advantages like low cost, high energy density, and high safety. Recently, Zn-air batteries have attracted growing attention because of their lower toxicity, low manufacturing cost, safety, and environmental benignity, in addition to high energy density. Single-atom catalysts, as suitable alternatives to Pt-based catalysts, have been suggested as oxygen electrocatalysts for Zn-air batteries owing to the many benefits like great catalytic performance, electronic properties, 100% atom utilization, and good reusability. On the other side, recently, dual-atom catalysts have emerged as powerful candidates for Zn–air batteries. Compared to single-atom catalysts, dual-atom catalysts have higher metal loading, flexible active sites, and better catalytic performance, so, more opportunities for electrocatalysis. An increasing number of reports have been published lately on the Zn–air batteries over dual-atom catalysts. In this chapter, a comprehensive survey of recent research progress about metal–air batteries is provided.

This chapter delves into the realm of multi-atom catalysts in the context of metal-air batteries. It provides a comprehensive exploration of their significance, spanning from the fundamentals of metal-air batteries to the catalytic mechanisms involved. It delves into how multi-atom catalysts enhance battery performance, featuring case studies and highlighting their role in applications such as electric vehicles and grid storage. Additionally, it scrutinizes the challenges and prospects of these catalysts in terms of sustainability and economic implications. This chapter serves as a roadmap to understanding the transformative potential of multi-atom catalysts in advancing energy storage solutions and fostering a more sustainable energy landscape.

Lithium-sulfur batteries (LSBs) are recognized as a prospective contender for future-generation electrochemical energy storage technologies due to their high theoretical energy density, affordable price, and ecological sustainability. However, challenges such as the slow redox kinetics of sulfur species and the shuttle effect cause a significant amount of capacity loss and polarization. These problems have been addressed using a variety of methodologies, such as physical barriers, chemical adsorption techniques, and electrocatalysts, which have improved the rate capability and cycle performance of sulfur electrodes. Recently, the integration of single-atom catalysts (SACs) with high catalytic efficiency has been introduced in LSBs to expedite sulfur conversion kinetics, aiming to boost their conversion rates. This chapter provides a concise overview of recent advancements in enhancing the electrochemical performance of LSB cathodes through the incorporation of various SACs. It delves into the catalytic mechanisms employed by SACs and explores synthesis methods, including the spatial confinement approach and coordination design strategy. This chapter also discusses challenges in designing high-performance sulfur electrodes and proposes potential solutions.

Dual-atom catalysts for metal-sulfur batteries are a type of catalyst made up of two metal atoms that work together to improve the performance of metal-sulfur battery systems. These catalysts are intended to improve the electrochemical processes that take place in the battery, resulting in increased energy storage capacity and overall battery performance. The bidirectional conversion between metal and metal sulfide during charge and discharge cycles is a critical mechanism for energy storage in metal-sulfur batteries. However, this conversion process is slow, resulting in low battery efficiency and a short cycle life. Dual-atom catalysts seek to overcome these issues by enhancing reaction kinetics and offering more efficient catalytic sites. The appropriate metal pairings for dual-atom catalysts are determined by a variety of criteria, including the individual battery chemistry and the required electrochemical processes. Platinum–Nickel (Pt–Ni), iron–cobalt (Fe–Co), Palladium–Cobalt (Pd–Co), Cobalt–Tungsten (Co–W), Molybdenum phosphide (MoP) and Zinc–cobalt (Zn–Co) are examples of metal pairings utilised in dual-atom catalysts for metal-sulfur batteries. The use of dual-atom catalysts in metal-sulfur batteries has yielded encouraging results in terms of increased battery performance. However, further research is needed to optimise these catalysts, understand their underlying processes, and investigate their scalability and cost-effectiveness for actual applications in metal-sulfur battery systems.

Metal-sulfur batteries offer promising energy density and cost-effectiveness, yet grapple with challenges like limited conductivity and rapid capacity degradation. The advent of multi-atom catalysts has revolutionized these batteries, addressing these issues. This chapter explores the design, synthesis, and performance of such catalysts, initiating with an overview of the challenges faced by metal-sulfur batteries and the necessity for enhanced catalysts. It delves into multi-atom catalysts, emphasizing their distinctive features and synthesis methods. The intricate interplay between composition, morphology, and structure is scrutinized for effective catalyst design. Advanced characterization approaches are highlighted for comprehending electrochemical behavior. The chapter discusses contemporary research showcasing the transformative potential of multi-atom catalysts in metal-sulfur batteries, encompassing catalytic activity, charge transfer kinetics, polysulfide conversion, and cycling stability. The conclusion addresses future prospects and challenges, underscoring the continual need for research to optimize catalyst design, scalability, and long-term stability for practical integration into large-scale energy storage systems. In summary, the chapter serves as a substantial resource for academia and engineering, providing a comprehensive overview of the pivotal role played by multi-atom catalysts in advancing metal-sulfur battery technology.

Liquid fuel cells (LFCs) are promising green energy conversion devices that can operate with a series of liquid fuels, such as methanol, ethanol, glycerol, ethylene glycol, formic acid, and glucose. In addition, their bio-obtained analogs can also be utilized, such as bioethanol obtained from non-food sources or crude glycerol, which is an undesired byproduct during biodiesel production. These fuels require catalysts to galvanically convert the chemical energy confined in their molecules into electricity. Currently, the best materials for the electrocatalytic oxidation of liquid fuels are noble metals, especially platinum-group metals (PGMs). Consequently, the cost of LFCs is increased by the catalyst’s contribution. Thus, new solutions are required for the development of cost-effective catalysts. In this sense, single-atom catalysts (SACs) are promising materials for LFCs because they enable effective metal utilization owing to their atomic distribution, and their activity is improved because of the increased reactivity of active sites owing to the promotion of uncoordinated sites. In this chapter, SACs for alcohol oxidation reactions are revised, focusing on physiochemical methods to detect SACs and the reactivity of outstanding SACs based on PGMs and non-PGM materials. It is found that the reactivity of SACs based on non-PGMs can be boosted, displaying superior activity compared to benchmarked nanoparticulated catalysts.