Electrochemical Desalination for a Sustainable Water Future

Fresh water is required to sustain life. However, the world is facing a global challenge to reliably supply its population with safe water due to shortages stemming from population growth, climate change, contamination of available fresh water supplies, and public policy. Presently, the United Nations estimates that one third of the world’s population ( 2.4 billion people) is living in water-stressed regions, meaning the annual water supply is <1700 m per person. Even more alarming, this number is expected to approach two thirds of the world’s population by 2025. Water shortages are not just limited to those living in arid or developing regions; the effects are now being acutely felt by those living in fresh water-rich environments. Increasing the availability of fresh water is a complex problem that does not have one simple solution. Consequently, technological developments providing a synergy of solutions will likely be required to address the world’s water challenges. The first step toward ensuring water for all is the efficient use and conservation of currently available fresh water supplies. Encouragingly, there are examples in the developed world of per-capita water use decreasing due to more efficient agricultural, industrial, and personal practices. Nevertheless, similar to petroleum reserves, continued economic development of populous countries such as China and India will exert new stresses on world-wide water resources. The available amount of water on Earth is relatively constant due to the hydrological cycle. However, supplies vary with time and location, therefore making localized water shortages commonplace. Table 1 shows that only about 2.5% of water available on Earth is fresh water (<0.05% salts by weight). Of this amount, more than half is locked in glaciers and permanent ice, while remaining supplies are increasingly becoming contaminated with difficult-to-remove impurities. Importantly, about 97.5% of the world’s water supply is contained in easily accessible saline reservoirs, with around 1.0% being brackish groundwater (0.05–3.0% salts) and the remaining 96.5% being seawater (3.0–5.0% salts). This suggests that the vast amounts of saline water could provide a nearly unlimited fresh water supply if coupled to an energy-efficient desalination technology. Here, we present many of the underlying concepts guiding the development of desalination technologies, while highlighting a new electrochemical approach, electrochemically mediated desalination (EMD), that our groups are currently developing. Although not comprehensive, this article aims to provide an introduction to the broad field of desalination, including modern thermal, membrane, and electrochemical technologies. We are particularly enthusiastic about the opportunities available to electrochemists and hope that this article will inspire new electrochemical desalination technologies. Discussions of the environmental impacts of desalination, along with many of the other novel desalination strategies being developed, inWe present an introduction to the broad field of desalination by providing a brief review of modern thermal, membrane, and electrochemical technologies. However, the main focus of this article is to introduce a fundamentally new and potentially powerful electrochemical approach to desalination: electrochemically mediated desalination (EMD). EMD is a membraneless desalination method that uses a simple power supply to oxidize a small fraction of the chloride ions present in seawater. This results in the generation of a local electric field gradient, which consequently separates ions to produce partially desalted water.