Electrochemical Science for a Sustainable Society

This chapter is a reproduction of an article written by Prof. J. O’M. Bockris published in Journal of Solid State Electrocehmistry (2011) 15:1763–1775. In this article, he described his own professional life devoted to electrochemistry with stories of his colleagues. Minor editorial changes were made by the editor to meet the style of this book.

This chapter deals with the concept of “hydrogen economy”, which was introduced by John O.M’ Bockris in 1972. We summarize the fundamental principles and the progress for the reactions relevant to the hydrogen economy, namely the hydrogen and oxygen evolution for water electrolyzers, and the hydrogen oxidation and oxygen reduction for fuel cells. The activity of each reaction can be correlated to a single descriptor, i.e. the adsorption energy of a key reaction intermediate, following a volcano-type relationship. Highly active materials can be prepared with the aid of modern computational and experimental tools. Nevertheless, to develop catalysts that are substantially more active and reach the performance of ideal catalysts, the focus must be placed on materials that can break the energetic scaling relations between intermediates. The systems of choice are acidic water electrolyzers or fuel cells, using noble metals for the catalytic material, despite the great progress made in the field of alkaline systems. However, to realize the concept of hydrogen economy on a large scale, the electrode material for either reaction must combine activity, stability and abundance.

A brief overview is presented of the general topic of fuel cells as it relates to the work of John Bockris and was inspired by him. We trace some of the historical development of the field, starting in 1839 with Sir William Grove, up to the present, with some comments on the proliferation of fuel cells in electric vehicles and residential electric power units. We also illustrate some of the development of the field with examples from our own research.

A theory of electrocatalysis developed in our group is presented and related to other theories of electrochemical electron transfer. As an example, the theory is applied to the first step in oxygen reduction on silver in alkaline media. It is shown, that this step occurs in the outer sphere mode.

In this chapter, an approach to kinetic studies on single crystal platinum electrodes is attempted. The selected reactions are those called structure-sensitive, involving chemisorption steps of reactants and/or intermediates that clearly reflect site-dependent adsorption energies. For this reason, it is important to define the type of sites involved in the reaction and describe how it is possible to characterize them under electrochemical conditions. The reactivity of the different surfaces is tested against a classical probe reaction: the CO stripping in acidic and alkaline solutions. The changes observed when dissolved CO is also present are also shown. The oxidation of formic acid is then discussed, taking into account the existence of a dual-path mechanism that leads to surfaces poisoned by CO. In order to extract relevant kinetic information, the two reactions should be separated, in such a way that the experimental current could be safely assigned to the active intermediate route alone. This is discussed for different orientations and different acidic solutions. The more complex case of ethanol oxidation, which also involves CO poisoning as a result of the C–C bond breaking, a reaction step that is sensitive to the surface structure, anion adsorption and pH, is briefly described. Finally, ammonia oxidation in alkaline solution, an extreme electrocatalytic reaction that only occurs at surfaces having platinum sites with square symmetry, is addressed.

To understand how electrochemical processes proceed at electrode/electrolyte interfaces and to improve the efficiencies of these processes, it is essential to probe these processes in situ real time. Thus, the developments of in situ techniques have been carried out very intensively for a long time. Thanks to the technological advancement in electronics, optics, quantum beams, and nanomaterials, various in situ techniques, which are capable of determining molecular, geometric, and electronic structures at electrochemical interfaces, have been developed in the last several decades and they are applied to a wide range of electrochemical interfaces from both fundamental and practical points of view. Here, various in situ techniques are described with historical aspects, several key innovations related to the techniques, and a few examples for the techniques to be applied.

An extensive demand for rechargeable batteries from environmental problems due to CO₂ emission was described in the introduction. Then, general information about several kinds of batteries for energy storage and electric vehicle applications are described. Specially, lead acid battery, lithium ion battery, sodium-sulfur battery, and redox-flow battery have been discussed based on electrochemical reactions occurring in the practical cells. The energy density of each battery was also discussed in detail based on not only material sciences but also battery technologies. In the future, higher energy density is strongly required for future rechargeable batteries. In the final section, research and development of next generation batteries are involved in this chapter.

Inorganic ionic liquids such as Na[FSA]-K[FSA] and inorganic–organic hybrid ionic liquids such as Na[FSA]-[C₃C₁pyrr][FSA] (C₃C₁pyrr =N-propyl-N-methylpyrrolidinium, FSA = bis(fluorosulfonyl)amide) and Na[FSA]-[C₂C₁im][FSA] (C₂C₁im = 1-ethyl-3-methylimidazolium) were investigated as potential electrolytes for sodium secondary batteries operating in the temperature range of 253–363 K. The cyclic voltammetry revealed that the electrochemical windows of more than 5 V at 363 K, and electrochemical deposition/dissolution of sodium metal reversibly occurs at the cathode limit potential. Considering their non-volatility, non-flammability and inexpensiveness, these salt mixtures are highly promising as a new class of electrolytes for sodium secondary batteries. The full cell tests employing NaCrO₂ and hard carbon as positive and negative electrode materials, respectively, revealed the high performance of the ionic liquid electrolytes for sodium secondary batteries.

The passive film on iron has provided positive benefits to the longevity of iron structures since antiquity. As the benefits of passivity of iron became recognized, debates among scientists developed over the possible mechanisms by which the very thin (2–3 nm) passive layer could impart substantive corrosion resistance. The mechanisms of passivity that impart unique properties to passive iron have been studied and debated for decades. In recent years, equipment that is sufficiently advanced for surface studies at an atomic level has been used to explore the mechanisms of passivity and, in combination with electrochemical studies, to characterize the chemical composition, physical structure, and electronic properties of the passive film on iron. The evolution of the concepts and theories of the passivity of iron are reviewed in this paper, beginning with the earliest observations and summarizing the developments that have become possible as a result of advances in instrumentation and surface analytical methods. Effects of temperature, texture, and hydrodynamics on the mechanisms of passivity of iron are discussed.

Global demand for energy is increasing at a fast rate especially in developing economies such as India, China, and Indonesia with heavy reliance on fossil fuels. The CO₂ levels in the atmosphere have increased to over 400 ppm. This combined with increase in the intensity of other pollutants (NO_x, SO_x, CO, methane, particulate matter, etc.) in the atmosphere is a real concern for the environment. With the major objective of reducing concentration of greenhouse gases and other pollutants and to increase reliability and security of energy supply for a sustainable future, significant progress is being made in the development and deployment of technologies and processes around renewable energy with solar and wind playing a dominant role. However, solar energy is not available in high intensity all around the word and thus there is a need for transporting energy from one place to other. Solar fuels are energy carriers and means of transporting solar energy in the form of easily transportable fuels and these are generated by embedding solar energy in the form of heat or electricity or both in water, CO₂, and fossil fuels. A number of different technologies and processes (electrolytic, solar thermal, solar thermochemical cycles, chemical looping, solar assisted reforming of natural gas, solar assisted coal/biomass gasification, photo-electrochemical, and photo-biological) for the production of major solar fuels (H₂, CO, syngas, methanol, and ammonia) are briefly discussed and reviewed in this chapter.