Electrochemical engineering

Electrochemical engineering is the branch of chemical engineering dealing with the technological applications of electrochemical phenomena, such as electrosynthesis of chemicals, electrowinning and refining of metals, flow batteries and fuel cells, surface modification by electrodeposition, electrochemical separations and corrosion. This discipline is an overlap between electrochemistry and chemical engineering.
According with the IUPAC, the term "electrochemical engineering" is reserved for electricity intensive processes for industrial or energy storage applications, and should not be confused with "applied electrochemistry", which comprises small batteries, amperometric sensors, microfluidic devices, microelectrodes, solid-state devices, voltammetry at disc electrodes, etc.
More than 6% of the electricity is consumed by large-scale electrochemical operations in the US.
Scope.
Electrochemical engineering combines the study of heterogeneous charge transfer at electrode/electrolyte interphases with the development of practical materials and processes. Fundamental considerations include electrode materials and the kinetics of redox species. The development of the technology involves the study of the electrochemical reactors, their potential and current distribution, mass transport conditions, hydrodynamics, geometry and components as well as the quantification of its overall performance in terms of reaction yield, conversion efficiency, and energy efficiency. Industrial developments require further reactor and process design, fabrication methods, testing and product development.
Electrochemical engineering considers current distribution, fluid flow, mass transfer, and the kinetics of the electro reactions in order to design efficient electrochemical reactors.
Most electrochemical operations are performed in filter-press reactors with parallel plate electrodes or, less often, in stirred tanks with rotating cylinder electrodes. Fuel cell and flow battery stacks are types of filter-press reactors. Most of them are continuous operations.
History.
This branch of engineering emerged gradually from chemical engineering as electrical power sources became available in the mid 19th century. Michael Faraday described his laws of electrolysis in 1833, relating for the first time the amount of electrical charge and converted mass. In 1886 Charles Martin Hall developed a cheap electrochemical process for the extraction of aluminium from its ore in molten salts, constituting the first true large-scale electrochemical industry. Later, Hamilton Castner improved the process aluminium manufacturing and devised the electrolysis of brine in large mercury cells for the production of chlorine and caustic soda, effectively founding the chlor-alkali industry with Karl Kellner in 1892. The next year, Paul L. Hulin patented filter-press type electrochemical cells in France. Charles Frederick Burgess developed the electrolytic refining of iron ca. 1904 and later ran a successful battery company. Burgess published one of the first texts on the field in 1920. During the first three decades of the 20th century, industrial electrochemistry followed an empirical approach.
After the Second World War, interest focused towards the fundaments of electrochemical reactions. Among other developments, the potentiostat (1937) enabled such studies. A critical advance was provided by the work of Carl Wagner and Veniamin Levich in 1962 who linked the hydrodynamics of a flowing electrolyte towards a rotating disc electrode with the mass transport control of the electrochemical reaction through a rigorous mathematical treatment. The same year, Wagner described for the first time "The Scope of Electrochemical Engineering" as a separated discipline from a physicochemical perspective. During 60s and 70s Charles W. Tobias, who is regarded as the "father of electrochemical engineering" by the Electrochemical Society, was concerned with ionic transport by diffusion, migration, and convection, exact solutions of potential and current distribution problems, conductance in heterogeneous media, quantitative description of processes in porous electrodes. Also in the 60s, John Newman pioneered the study of many of the physicochemical laws that govern electrochemical systems, demonstrating how complex electrochemical processes could be analysed mathematically to correctly formulate and solve problems associated with batteries, fuel cells, electrolyzers and related technologies. In Switzerland, Norbert Ibl contributed with experimental and theoretical studies of mass transfer and potential distribution in electrolyses, especially at porous electrodes. Fumio Hine carried out equivalent developments in Japan. Several individuals, including Kuhn, Kreysa, Rousar, Fleischmann, Alkire, Coeuret, Pletcher and Walsh established many other training centers and, with their colleagues, developed important experimental and theoretical methods of study. Currently, the main tasks of electrochemical engineering consist in the development of efficient, safe and sustainable technologies for the production of chemicals, metal recovery, remediation and decontamination technologies as well as the design of fuel cells, flow batteries and industrial electrochemical reactors.
The history of electrochemical engineering has been summarised by Wendt, Lapicque, and Stankovic.
Applications.
Electrochemical engineering is applied in industrial water electrolysis, electrolysis, electrosynthesis, electroplating, fuel cells, flow batteries, decontamination of industrial effluents, electrorefining, electrowinning, etc. The main example of an electrolysis based process is the Chloralkali process for production of caustic soda and chlorine. Other inorganic chemicals produced by electrolysis include:
Conventions.
The established performance criteria, definitions and nomenclature for electrochemical engineering can be found in Kreysa et al. and an IUPAC report.