Electrocatalysis in Balancing the Natural Carbon Cycle, 1 by Yaobing Wang

Electrocatalysis in Balancing the Natural Carbon Cycle



Yaobing Wang





Logo: Wiley


In recent years, sustaining the carbon cycle and producing valuable fuels that may considerably reduce dependence on fossil fuels using electrocatalysis has grown. A great deal of interest has arisen, leading to an increase in young researchers entering this area. This book focuses on the aspects of efficient redox catalysis, such as water and carbon dioxide electrolysis toward hydrogen and fuel‐based energy systems, respectively, and remarkable energy technologies such as fuel cells and metal–air batteries. An introduction and recent progress are provided, emphasizing reaction conversions developments over various types of electrocatalysts. In addition, the book includes chapters that attract not only experimentalists but also theoretical chemists who have interest in the electrocatalyst design.

The book comprises 10 parts. The first three parts provide a solid introduction for the electrocatalytic carbon cycle addressing water splitting, carbon dioxide reduction, and its counterpart, the oxidation of small organic molecules, followed by detailing each related reaction in separated part: (i) part IV presents water‐splitting devices after describing the key fundamental research developments of water oxidation and reduction reactions, (ii) part V includes hydrogen and oxygen‐related electrocatalytic aspects with well‐defined fuel cell and batteries models, (iii) part VI illustrates the oxidation of C1 and C2+ molecules as up‐and‐coming advanced power systems, and (iv) part VII reviews the fundamentals in carbon dioxide reduction reaction including well‐defined catalytic electrodes as well as the current and next generation of its devices. From the experimentation developments to the theoretical approaches, part VIII focuses on the kinetics and thermodynamics of the reactions aforementioned. For the most popular current motifs, the fundamentals of computational screening, descriptors, and modeling are outlined, as well as their application toward catalyst design direction instead of trial‐and‐error approach. While emerging the advanced characterizations addressing the in situ techniques become shining, part IX includes modern analytical methods to uncover the surface evolution/reconstruction of a given catalyst under the electrocatalytic conditions, which drive the electrochemical surface science research toward confirming the real active sites of a desired catalytic performance. The book ends with part X evaluating the electrocatalytic carbon cycles and its involved redox reactions. The parts are detailed as follows:

In Chapter 1, Prof. Yaobing Wang discusses the motivation for writing this book introducing the natural carbon cycle (NCC) and the emergence of its challenges in multiple environmental and ecological systems due to the overuse of fossil fuels and the increasingly severe energy crisis. Prof. Yaobing Wang highlights the electrochemical carbon cycle (ECC) as an endorsed solution for such concerns. In Chapter 2, Mr. Wei Wang and Dr. Jiafang Xie explain the various aspects in NCC from organic to inorganic cycle and vice versa, as well as anthropogenic carbon standpoint. In Chapter 3, Miss Zhen Peng and Dr. Jiafang Xie present the possible involved reaction in the ECC including oxygen reduction reaction (ORR), hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), electrochemical carbon dioxide reduction reaction (ECDRR), and small molecule oxidation reaction (MOR) from mechanistic viewpoint and their evaluation parameters such as Faradic efficiency (FE), Tafel slope, current density, and onset potential. In Chapter 4, Miss Rui Yang and Dr. Yiyin Huang go through water‐splitting reactions in various pH media and evaluation of their catalytic parameters such as turnover frequency (TOF), stability, and FE. In Chapter 5, Miss Rui Yang and Dr. Yiyin Huang specify the regular OER over various electrocatalytic materials and further consider the photo‐assisted OER. As HER is involved in water splitting, Miss Rui Yang and Dr. Yiyin Huang explore it in Chapter 6 over noble and non‐noble catalysts, in addition to the overall device. In Chapter 7, Mr. Zipeng Zeng, Dr. Parameswaram Ganji, and Dr. Yiyin Huang cover the basic parameters for hydrogen oxidation reaction (HOR) and ORR. In addition, they review the catalytic materials, the possible pathways, and the final products of HOR and ORR in Chapters 8 and 9, respectively. In Chapter 10, the focus of Mr. Zipeng Zeng, Dr. Parameswaram Ganji, and Dr. Yiyin Huang goes to H2 fuel cell and metal–air batteries as promising devices in which these reactions undergo. Moving to small MOR, Miss Xueyuan Wang and Dr. Yiyin Huang outline the measurement conditions in Chapter 11. MOR could be classified into C1 and C2+ reactants; thus, Miss Xueyuan Wang and Dr. Yiyin Huang describe C1 (including methane, methanol, and formic acid) and C2+ (including ethanol, glucose, ethylene glycol, and glycerol) reactions and their advances in Chapter 12 and 13, respectively. Miss Xueyuan Wang and Dr. Yiyin Huang give a general model and the advantage of the related typical device, the direct liquid fuel cell (DLFC) in Chapter 14. Parallel with schematic content, Mr. Rahul Anil Borse and Dr. Jiafang Xie elaborate the experimentation fundamentals (Chapter 15), the electrocatalytic advances of the ECDRR on various catalytic materials (Chapters 16 and 17); in addition, the available fabricated devices and their aspects (Chapter 18). Transferring from the experimentations into theoretical approach, Mrs. Aya Gomaa Abdelkader Mohamed provides more fundamental insights into the catalytic process addressing the electric double layer, the thermodynamics and kinetics, and the electrode potential effects in Chapter 19. In Chapter 20, Mrs. Aya Gomaa Abdelkader Mohamed covers the computational theories (such as DFT) and their principles such as reactivity descriptors and scaling relationships, which are related into the electrocatalytic process. Mrs. Aya Gomaa Abdelkader Mohamed explores how these principles can guide the rational design toward high‐performance and desired catalyst in Chapter 21. Moreover, Mrs. Aya Gomaa Abdelkader Mohamed reveals the computational applications to get deep understanding of the electrocatalytic mechanism for ORR, OER, HER, HOR, ECO2RR, and various MOR, as well as the electrocatalytic environment, and analyze their kinetics in Chapter 22. Recently, the in situ characterizations have become potential to identify the real active sites. Therefore, Mr. Mostafa Ragab Hassan and Mrs. Aya Gomaa Abdelkader Mohamed cooperate to give a basic background for the most reported in situ characterizations, which are classified into optical, X‐ray, mass, electron‐based techniques in Chapter 23. The investigation of a given catalyst in several electrocatalytic reactions by the in situ analysis is addressed in Chapter 24 by Mrs. Aya Gomaa Abdelkader Mohamed and Mr. Mostafa Ragab Hassan in different aspects such as probing the real active sites, determining the reaction mechanism, evaluating the catalyst stability/decay, and providing interfacial‐related insights. Finally, Dr. Jiafang Xie proposes the anthropogenic ECC solution to supplement unbalanced NCC from a global viewpoint in which the advances in critical electrocatalysts and performance for ECDRR (Chapter 25) and electrochemical fuel oxidation (Chapter 26) are presented. Then, several key indexes, external managements, and general principles are proposed to evaluate, support, guide the overall efficiency of ECC in Chapter 27.

This multidisciplinary work is not just a reference for the electrochemistry researchers, but also a handy book for advanced graduate‐level students in surface science‐, engineering‐, and theoretical‐related courses, especially those with interest in developing novel catalysts for efficient energy conversions, as well as the experienced researchers seeking to expand their scope.

19 November 2020

Yaobing Wang

Fujian Institute of Research

on the Structure of Matter

Chinese Academy of Sciences

Fuzhou, Fujian



I much acknowledge the dedication of all the authors who worked on this work. Without their effort, the book could not have been finished. My appreciation also goes to Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, my family, my wife, and two daughters, as well as Wiley Publishing, specially Lifen Yang, Katherine Wong, etc.

Part I

Electrocatalysis is considered a core technique for sustaining the carbon cycle and producing valuable fuels as an additional benefit. In recent years, a great deal of interest has arisen in efficient redox catalysis, such as water and carbon dioxide electrolysis toward hydrogen and fuel‐based energy systems, respectively, and remarkable energy technologies such as fuel cells and metal–air batteries. Understanding the fundamental aspects and the catalytic behavior of such reactions plays a considerable role in further commercializing electrocatalytic energy devices, helping to close the carbon cycle. In this part, we are going to discuss the motivation for writing this book and presenting a preface to its contents. Our hope is that this book will prove useful to researchers already familiar with electrocatalysis but interested in acquiring more insights and in‐depth digestion of state of the art of their catalysis research.


Carbon cycle is the basic cycle on earth to maintain all the life forms. In the earth, there are four primary carbon pools [1]. Among them, the natural carbon cycle (NCC) mainly refers to the cyclic change of carbon in the three‐carbon pools of atmospheric carbon pool, marine carbon pool, and terrestrial ecosystem carbon pool [1–4]. The atmospheric carbon has a direct influence on human life; therefore, it attracts great attention from researchers. The carbon in the atmospheric carbon pool mainly exists in the form of CO2 gas. The basic process of the NCC can be expressed as follows [1,5]: CO2 in the atmosphere is solidified into organic carbon through photosynthesis of plants and stored in plants. Part of the organic carbon in plants releases CO2 into the atmosphere through the plant's respiration (i.e. autotrophic respiration), the consumption of organic carbon by animals, and the decomposition of organic matter by microorganisms (i.e. heterotrophic respiration), forming a terrestrial ecology system carbon cycle process.

Since the industrial revolution and with the rapid world population/economic expansion, people utilized more and more fossil fuels for providing raw materials and electrical power, etc. [6]. Challenges in multiple environmental and ecological are emerging due to the overuse of fossil fuels and the increasingly severe energy crisis [7]. The results are that the NCC has been increasingly broken, leading to unavoidable sustainability in energy and environment, threatening the survival of human society. Thus, various strategies and various renewable energy technologies have been developed from all aspects to solve the broken NCC and maintain the sustainability of human society and the economy [8,9]. These techniques include fuel cells, CO2 electrolysis, metal‐air batteries, water splitting, and so on. All of these techniques consist of the kernel and/or secondary components in artificial nature carbon cycle (ACC) to supplement for the NCC with synergistic effects [5,7]. These techniques are mainly powered by solar‐derived electricity, which were also defined as the artificial electrochemical carbon cycle (ECC). The ECC mainly involves electrochemical oxidation of chemicals and fuels into CO2 (CO2 liberation) and electrochemical reduction of CO2 into value‐added chemicals/fuels (CO2 fixation), and also other fuel storage and transport, and other secondary reactions for supporting the carbon‐based electrochemical reactions.

For the realization of ECC, the extensive fundamental and utilitarian electrochemical processes, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), small organic molecule oxidation reaction, hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), and electrochemistry carbon dioxide reduction reaction (ECDRR), were involved. In the water splitting processes [10], water oxidation (OER) occurs on the anode, and four‐electron transfer is needed for a complete OER. At the same time, the generated electron and proton will be combined on the cathode and releasing H2 from the cathode. In various fuel cells [11,12], HOR via the two‐electron transfer process and various small organic fuel (ethanol, formic acid, methanol, glucose oxidase, ethylene, glycerol, glycol, etc.) oxidation occur on the anode, while ORR takes place on the cathode. The cathode of metal‐air batteries [13] also employs ORR processes. For the CO2 electrolysis [14], CO2 was electrochemically transformed into various fuels, as mentioned earlier, via different electron‐transfer processes.

The generally sluggish reaction kinetics is always a bottleneck that limits the overall performance of the new energy devices, hindering their progress of commercialization [15,16]. To drive these electrochemical processes, electrocatalysts are required. Noble metal catalysts are widely used in these electrocatalytic processes due to their high activity and stability. On the other hand, the high cost hinders their commercialization. Various non‐noble metal catalysts were also developed, such as carbon materials, polymer, transition metal materials, and metal‐organic materials [15]. With the development of nanotechnology and nanoscience over the past decades, the research mode for developing electrocatalysts has shifted gradually from the traditional trial‐and‐error methods to the accurate design and fabrication of nanocatalysts at atomic and molecular levels [15,17,18]. Besides, other factors in the electrochemical devices, such as the device structure, electrolyte, electrode configuration, and operation temperate, should be considered toward the high performance of the devices. Among these controllable factors, the electrocatalyst design is still among the core factor. To achieve the rational design of electrocatalyst for highly efficient electrocatalytic reaction processes, studies on the active sites' recognition, reaction mechanism, and kinetic and thermodynamic processes should be conducted. In this sense, computational methods combined with in situ characterization techniques allowed the researcher to realize an in‐depth and comprehensive understanding of realistic reaction conditions into the nature of the active sites and its interaction with reactants, intermediates, and products and the final overall catalytic processes.

In this book, we will discuss the reaction mechanism and core reaction parameters (e.g. turnover frequency [TOF], onset potential or overpotential, stability, Faradaic efficiency, partial current density) of these electrochemical reactions strongly to the ECC and summarize the advances of various catalysts in terms of the categories to gain an overview on the design principles for electrocatalysts toward various electrochemical reactions. The device categories and advances will also be summarized, with respect to the electrolyte, device structure, electrode, and external environment controls. Then, theoretical calculations for these electrocatalytic reactions were introduced in terms of background, concepts, processes, and applications. Besides, an overview of the common and the most crucial in situ characterization techniques was summarized to assist the theoretical calculations study and help the electrocatalyst design. Further, we have summarized the advances on electrochemical reactions highly related to the ECC, that is, ECDRR, and fuel oxidation for the chemical conversions including CO2/CO, CO2/HCOOH, CO2/CH3OH, and CO2/CH3CH2OH, along with presenting the mechanistic understanding and proposed key indexes, general principles, and external managements for evaluating and optimizing the overall ECC efficiency. Finally, current challenges and future perspectives for promoting ECC to supplement NCC were concluded. It is believed that this book will provide a comprehensive, deep‐going, and cutting‐edge introduction on the ECC and related electrocatalysis.


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Part II
Natural Carbon Cycle

Nature's photosynthesis uses green plants to absorb carbon dioxide (CO2) from the atmosphere, convert it into glucose and release oxygen with the participation of water, and organisms reuse glucose to synthesize other organic compounds. Only when enough geological time is given can new fossil fuels be formed naturally. Due to the continuous massive consumption of fossil fuels by human beings, a large amount of CO2 is produced. These anthropogenic CO2 emissions exceed the recovery capacity of natural CO2, causing serious damage to the environment. In order to supplement the natural carbon cycle, the researchers proposed and developed a feasible chemical cycle of anthropogenic CO2. Carbon dioxide can be captured from the atmosphere or industrial production through absorption technology. Then it can be converted into fuel through feasible chemical conversion. For example, by electrochemical reduction method, CO2 can be efficiently converted into reusable chemical products under normal temperature and pressure, such as carbon monoxide (CO), formic acid (HCOOH), methane (CH4), ethylene (C2H4), ethanol (CH3CH2OH), etc. The required renewable raw materials, water, and CO2 can be used anywhere on earth. The energy required for the synthetic carbon cycle can come from any alternative sustainable clean energy, such as solar energy, wind energy, geothermal energy, and even safe nuclear energy. When fossil fuels become scarce, the anthropogenic CO2 cycle provides a way to ensure a sustainable future for humanity.