Methods for Electrocatalysis

Altering/replacing the rare elements and noble metal like platinum (Pt), iridium (Ir) and ruthenium (Ru) with the earth abundant materials towards the energy devices have extended a lot of attention for the improvement of efficient electrocatalyst. In this chapter, we have focused on the earth abundant electrocatalysts primarily used for overall water splitting, oxygen reduction reaction (ORR) in fuel cells, O₂C reduction, N₂ reduction and detection of pollutants in water samples. The problem related to the non-noble metals electrocatalysts are their poor electrocatalytic activity, restricted active sites and also small mass transport properties. However, recent studies show that earth abundant materials can be a suitable/efficient candidate for these applications with optimized composition and nano-scale particle size, which will definitely accelerate their catalytic activity. In this chapter, we have focused on all these aspects of earth abundant electrocatalysts (EAEs) and discussed their future perspectives also.

Metal–organic frameworks (MOFs) have recently become prospective materials for electrocatalysis. MOFs constructed via coordination chemistry of inorganic metal nodes and organic ligands, possess the exclusive features over traditional inorganic or organic materials, which include ultrahigh porosity, large surface areas, structural tunability and high stability. Based on these features, MOFs are already being applied in storage and separation, catalysis, optoelectronics, drug delivery and biomedical imaging. Particularly, with the advantageous feature, MOFs have potential to work as efficient electrocatalysts for a variety of redox reactions, such as hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), oxygen evolution reaction (OER), etc. In this chapter, a discussion has been presented on MOFs, their composites, MOF-derived carbon materials and their performance as electrocatalysts. This chapter will inspire new research direction regarding the development of advanced electrocatalytic materials using MOFs.

The amount of energy that has being required to keep the well-being of our society is increasing continuously imposing an urgent need for renewable and less pollutant alternative energy sources to fossil fuels, whose consumption in internal combustion engines and electric power plants are responsible for unprecedented atmospheric pollution, particularly concentrated in large cities. Another consequence seems to be the general increase of temperature of the planet leading to climate changes and catastrophic extreme events. Thus, the possibility of reserves depletion and global environmental issues associated with its use are prompting the search for clean renewable energy sources, as well as the development of efficient and more robust energy storage systems. The most promising one for such a purpose is based on the splitting of water in a photosynthetic system to store the energy of Sun as hydrogen and oxygen. In order to realize such a technology, new more efficient electrocatalysts for oxygen and hydrogen evolution reaction based on single-atom catalysts, especially designed to exploit the maximum potentiality of the elements, are being developed, fueled by increasingly powerful theoretical modelling and characterization tools, thus paving broad roads towards a bright and sustainable society. The main advancements for preparation and characterization of such novel strategic materials are considered in this account. Furthermore, atomic scale modelling based on density functional theory is also discussed in the context of the unique electronic structure that leads to superior catalytic activity, highlighting its potential to advance this important scientific field.

In the last few years, much attention has been given to the design and fabricate efficient electrocatalysts for different applications in energy storage devices, electroanlytical sensors and organic synthesis. Nanocomposite materials have arisen as some of the most proficient electrocatalysts because of their exceptional physico-chemical and electronic properties. We focus our significant importance on different construction approaches for synthesis and applications of nanocomposites and their influence on inherent electronic and catalytic properties. Lastly, we discuss the applications and future prospects leading to develop advanced nanocomposites for efficient electrocatalysis.

Electro-catalysis is a fast growing process from the basic research to real time industrial applications. This is possible because of the major improvements achieved in this during the recent decades. Polymers are finding applications in several fields of science and technology, such as metallization of dielectric process, manufacturing of batteries, polymeric coatings, electro-chromic polishing, electro-magnetic protection, etc. One of the most important characteristic of any polymeric material is their ability to catalyze some reactions. This property not only helped for a better understanding about the polymer but also proved predictive capabilities for good catalysts. In addition to the latest theoretical advancements that have helped to improvise electro-chemical catalysts, the progress in the usage of new experimental methods is closely associated to polymer electro-catalysis research. In this chapter a detailed discussion on electro-catalysis of polymers is presented.

Oxygen evolution reaction is evinced as one of the main rate-determining steps for clean energy production, energy security supply and therefore for the evolution of a sustainable society. The production of clean energy, the security of energy supply (autonomy) and lower cost of energy supply constitute the main key points for a sustainable future. It is known, that a sustainable future can be achieved only if the current power supply shifts to other sources than the conventional ones; with the renewable energy sources and hydrogen fuel to own a leading role. The oxygen evolution reaction mechanism in acidic and alkaline media remains a mystery even today, after so many years of research activities. Bockris in 1954 and then Bockris and Huq in 1956 were the initial founders of the oxygen evolution reaction mechanism study. Then, many mechanisms were suggested and up-to-date many materials have been studied, with the metal perovskite oxides to be the most promising candidates. When this ‘mystery’ is solved, then a big step towards a sustainable future will become.

The photochemical water splitting to produce O₂ and H₂ is considered as the most promising, sustainable, renewable and cost-effective energy technology for the future. In photochemical water splitting process, the efficiency of H₂ and O₂ production rates depends on the properties of the selected semiconductor material. However, most of the semiconductors face various limitations which confines their water splitting efficiency. Different strategies could be implemented to improve the water splitting efficiency of semiconductors. Among them, loading of catalyst onto the water splitting material is known to be one of the effective strategy to enhance the H₂ and O₂ production rates. Given this, several catalytic materials have been explored and successfully utilized in efficient O₂ and H₂ production systems. In this chapter, we summarize some of the effective O₂ and H₂ production catalysts derived from noble metal, noble metal oxides, earth-abundant metals and oxides, metal phosphides and metal chalcogenides. The surface deposited catalysts were known to reduce the surface trap states, which decreases the charge recombination and acts as protective layer to minimize photo-corrosion of the light absorbing semiconductors. Conclusively, to explore the efficient catalysts for photochemical water splitting require more research contribution towards the understanding of the core reaction mechanism of catalytic process with the use of sustainable and stable materials.

Solar energy can be tapped and stored efficiently using photoelectrochemical (PEC) cells. PEC cell utilizes influx of photons to drive uphill chemical reactions and thereby transforming their inherent energy into chemicals bonds. PEC reaction is one of the most important reactions for generating hydrogen and oxygen. Moreover, as the reaction is reversed and hydrogen is combusted in presence of oxygen; water is obtained as by-product. A lot of research efforts are underway for realizing efficient photoactive material that can absorb sunlight in visible region and has proper straddling band edges that can oxidize and reduce water. The water oxidation half cell reaction also restrains the technology as water oxidation is slow at the surface of photoanodes compared to other loss processes. Semiconductor (SC) photoanodes modified with earth abundant electrocatalyst (EC) can be a important proposition for realizing electrodes with high photocatalytic activity and stability for proficient PEC splitting of water. This approach allows optimization of different processes such as photon absorption, charge separation and surface catalysis independently. The PEC reactions are catalyzed by electrocatalyst by lowering the activation energy. For PEC H₂ generation reaction, the main earth abundant electrocatalyst comprises of transition metal chalcogenides, carbides, phosphides, whereas for O₂ generation mixed transition metal oxides can be utilized. Bifunctional (HER/OER) electrocatalyst such as NiFeOOH and Co-Mn oxide nanoparticle can be used for PEC splitting of water. Hybridization of composite photoanodes, provide flexibility for adjustment of different components with different properties but raises new issues at the interfacial forefront.

The chapter presents the theoretical and experimental concepts of the phenomenon of cationic electrocatalysis during the discharge of complicated anionic complexes in molten salts. These ideas are based on the acid-base mechanism of formation of electrochemically active species (EASs). The essence of cationic electrocatalysis is the transformation of anionic complexes into a new active state under the action of cations with a strong polarizing effect. This leads to a change in the energy, electronic, and structural state of the anion, the formation of new EASs, a change in their composition, in the rate of EAS formation and charge transfer. The performed quantum chemical calculations allow one to conclude that the cationic composition of the melt catalyzes the formation of new EASs both in the bulk phase of the melt and at the electrode-melt interface. Using voltammetry, it was shown that the addition of Mg²⁺ cations to tungstate-containing melts leads to a change of the nature of the electrode process and to an increase of an order of magnitude in heterogeneous rate constant for charge transfer. The tungsten deposition potential shifts to the positive potential values up to the potentials of carbon deposition from CO₂. The proposed approach allowed us to realize in practice the synthesis of nanoscale powders of tungsten carbides and composite mixtures based on them by electrolysis of molten salt electrolytes. The obtained materials have a high potential for application for solving various tasks of electrocatalysis.

The increasing demand by energy and the current need of the replace fossil resources it is leading the research and development (R&D) sector to search by renewable feedstock and renewable processes. Thus, major emphasis is being put into sustainable technologies and environmentally benign. In this context, microalgae have been extensively exploited for their versatility and capacity of the produce a broad spectrum of bioproducts. In particular, the viability of these microorganisms to generate electrical energy from organic and inorganic residues is an attractive technological route. The use of microalgae in electrochemical systems has the potential to produce bioelectricity associated with bioremediation and wastewater treatment. This integration could be advantageously exploited to the development of a self-sustaining biobased system. In this sense, this chapter is intended to provide a overview of various aspects associated with the bioelectricity production from microalgae.

Among different methods of fabrication of electrocatalytic coatings, the electrodeposition seems to be the most convenient and widely used. The electrodeposition is an available, inexpensive, versatile, simple and fast technique which allows synthesizing materials with controlled composition, structure, surface morphology and electrocatalytic activity. This review reports recent trends, promising directions and novel approaches concerning cathodic electrodeposition and characterization of electrocatalytic coatings. A special attention is paid to the electrocatalysts based on electrodeposited nickel, iron, cobalt, copper, chromium, noble metals, their alloys and composites. The application of non-stationary current regimes (pulse current and linear potential sweep) as well as new type of plating baths (room-temperature ionic liquids and deep eutectic solvents) is highlighted. The influence of alloying and after-treatment (dealloying, selective anodic dissolution, etc.) on the electrocatalytic properties of electrodeposits is considered. Favorable influence of the formation of nanostructures upon the electrocatalytic performance of electrodeposited materials is shown. Potential ways for improving the electrocatalytic characteristics of electrodeposited coatings are described.

Electrochemical energy conversion technologies, such as polymer electrolyte fuel cells, Direct Methanol fuel cells and metal-air batteries are of supreme significance to attain sustainable energy for future use. Nanocomposite materials have fast emerged as promising candidates as a replacement to commercial and state-of-the-art electrocatalysts. They show remarkably increasing progress in electrocatalysis including oxygen evolution, oxygen reduction, CO₂ reduction, hydrogen evolution etc. Carbon support with high surface area provides better utilization of the electrocatalysts to escalate its activity. Electrocatalysis has been the subject of growing interest for many concerned people as it caters to the escalating needs of fuel production. Researchers and manufacturers are keen to cash in the burgeoning demand of nanocomposite based electrocatalyst materials and devices as they exhibit distinctive surface/size-dependent and simplistic tunable structures which are pivotal for the performance of electrocatalysis process. Regulation and modulation of electronic properties is realizable through adaption of various surface chemistry techniques. This chapter gives an insight to the application of nanocomposite materials in electrocatalysis and their properties which gives perspective to probe further in this rising field of research to expand scientific understanding and build upon the current body of work.

Electrocatalysis stands as a heart for realization of hydrogen gas (H₂) as a source of energy to replace conventional and traditional fossil fuel based energy. In this chapter, we present a comprehensive overview of the state-of-the-art molybdenum disulphide (MoS₂) nanostructures for application in electrolytic hydrogen evolution reaction (HER). MoS₂ is a crystalline compound consisting of Mo sandwiched between two sulfur atoms and can be identified in four poly-type structures, namely 1T, 1H, 2H and 3R. Firstly, the reaction accompanied with water splitting electrolysis, HER mechanisms as well as parameters to monitor HER reactions are discussed. Furthermore, the chapter describes different types of MoS₂ poly-types, chemical synthetic routes and key approaches to activate inert S-containing basal plane of MoS₂. This led to superior performance of new materials by combining the advantages of MoS₂ components and others. Finally, future integration approaches which can be used to attain MoS₂ with exposed edges and excellent electron transport channel are also outlined in this chapter.

The fast depletion of fossil fuels, the main energy sources, in addition to the emission of carbon dioxide (CO₂) from burning of these fuels intensifying the research for the development of alternative clean, sustainable and secure energy source. Hydrogen (H₂) is considered as one of the most promising alternatives that can play a significant role as a zero-carbon energy carrier with reduced fossil fuel dependence. Utilization of two of our most abundant resources, sunlight and water, for the production of hydrogen via mimicking the natural photosynthesis process by the photocatalytic water splitting by using a semiconductor photocatalyst is a fascinating way for the establishment of clean, sustainable and secure energy source. This chapter highlights the efforts that have been devoted for the development of photocatalysts that can efficiently harvest the maximum solar light for the photoelectrochemical water splitting into hydrogen and oxygen. The difficulties in achieving water splitting under visible light will be addressed. Furthermore, the strategies for overcoming these difficulties and approaches for improving the visible light response of the photocatalysts towards water splitting will be discussed.

Polymer electrolyte membrane fuel cells (PEMFCs) and metal air batteries are considered green and efficient electrochemical energy devices and both include reduction of oxygen at cathode during the working of device. Due to the sluggish reaction kinetics of ORR, it is considered the performance limiting factor and to cope with this issue scientists are trying to introduce low cost, highly durable and efficient electrocatalyst for cathode reaction. After the synthesis of catalyst material, different electrochemical techniques including Steady-state polarization, Cyclic voltammetry, Rotating disk electrode and Rotating ring disk electrode are used to check the performance and durability of ORR catalysts. In PEMFCs, water should be produced along with some heat by the 4-electron transfer reaction between oxygen, protons and the electrons. The reported ORR catalysts can be classified as platinum group metal catalyst, platinum group metal free catalyst and metal free catalysts. All the catalysts have their own pros and cons, while platinum supported carbon (Pt/C) is considered the state-of-the-art catalyst for both fuel cell and metal batteries.

This chapter reviews the history, the progress, development and achievement of electrocatalysis. We introduce some practical examples for electrochemical reactions as CO₂ reduction, hydrogen evolution and oxygen reduction reaction. Some examples of these anchored reaction using differents electrocatalysts cited metal oxide, carbon based material, alloy material, noble and precious metal, layered electrocatalytic materials, platinum-based electrocatalysts and electrocatalysts without Pt are cited.

In the process of developing a catalyst, understanding their structure and properties is considered essential as it is obligatory to improve their performance or to resolve a failure issue. Hence, the purpose of this invited chapter is to give a brief summary of various characterization tools specifically, X-ray Diffraction (XRD), Brunauer, Emmett, and Teller (BET) technique, Infrared Spectroscopy (IR), UV-visible spectroscopy, Electron microscopy, and Electrochemical techniques, where we discussed the principle, application, and challenges associated with the catalyst characterization. Also, in this chapter, we illustrated the analysis and interpretation of characterization data with an example for better understanding. These perceptive investigations of different characterization tools lead to the establishment of empirical relationships between various factors that govern catalytic activity.

Alkaline electrolyzed water hydrogen production technology is of great significance to the development of sustainable alternative energy. Although precious metal Pt is the best electrocatalyst for hydrogen evolution reaction (HER), its alkaline HER involves the two-step reaction of water dissociation and hydrogen recombination, which limits its development in alkaline electrolyzed water technology. Therefore, amount of interface chemistry of materials has been investigated to design catalysts with a large number of active sites and stability to improve the performance of alkaline HER. In this chapter, we summarize the interfacial chemical specificity of the Pt and Pt-based catalysts for controlling alkaline HER kinetics to boost the water dissociation step and hydrogen evolution efficiency. This is a guiding significance for the future of building renewable and sustainable energy systems.