Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.

The increasing popularity of nuclear energy necessitates development of new methods to treat water that becomes contaminated with radioactive substances. Because this polluted water comprises several dissolved species (not all of which are radioactive), selective accumulation of the radionuclides is desirable to minimize the volume of nuclear waste and to facilitate its containment or disposal. In this article, we use shock electrodialysis to selectively, continuously, and efficiently remove cobalt and cesium from a feed of dissolved lithium, cobalt, cesium, and boric acid. This formulation models the contaminated water commonly found in light-water reactors and in other nuclear processes. In a three-pass process, a consistent trade-off is observed between the recovery of decontaminated water and the percentage of cobalt removed, which offers flexibility in operating the system. For example, 99.5% of cobalt can be removed with a water recovery of 43%, but up to 66% of the water can be recovered if deionization of cobalt is allowed to drop to 98.3%. In general, the energy consumed during this process (ranging between 1.76 and 4.8 kW h m–3) is low because only charged species are targeted and virtually no energy is expended removing boric acid, the most abundant species in solution.

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The affordable and effective removal of traces of toxic heavy metal ions, especially lead, from contaminated drinking water in the presence of excess sodium or other competing ions has been a long-standing goal in environmental science and engineering. Here, we demonstrate the possibility of continuous, selective, and economical removal of lead from dilute feedwater using shock electrodialysis. For models of lead-contaminated tap water, this process can remove approximately 95% of dissolved lead (to safe levels below 1 ppb), compared to 40% of sodium ions, at 60% water recovery and at an electrical energy cost of only 0.01 kW h m −3 . We are able to fit and interpret the separation data with a pore-depth-averaged electrokinetic model that reveals the mechanisms for selective separation of lead ions. This selectivity is enabled by the faster transport of lead ions from the charged porous medium to the cathode stream, as well as their larger barrier to escape to the fresh stream compared to sodium ions. The experimental and theoretical results could be used to guide the development of low-cost, point-of-use systems for continuous removal of lead from municipal water.