Water and energy are inextricably linked. The two have shared a long technological and symbolic connection, which has led to what researchers in the field call the energy/water nexus.
The energy/water nexus refers to the relationship between the water used for energy production and the energy consumed to extract, purify, and deliver water. During the PRiME 2016 meeting in October, researchers from across the globe gathered together for the Energy/Water Nexus: Power from Saline Solutions symposium to discuss emerging technologies and how the interplay between water and energy could affect society now and in the future.
“It’s very hard to say energy and not say water in the same sentence. They are completely interconnected systems,” says Andrew Herring, co-organizer of the symposium and Colorado School of Mines professor. “You cannot have clean water without energy, and to have clean water, you have to have energy.”
Some of the most common research topics in the water/energy nexus are water purification, desalination, and cooling efforts to create energy sources. However, there is another subcategory of this field that is overlooked but could play a vital role in the development of future technologies: blue energy.
Potential of blue energy
The concept of blue energy – otherwise known as osmotic power – was developed upon the realization that through electrochemistry, researchers can create a concentration cell with salt water on one side and fresh water on the other, which results in a novel way to power devices.
But how exactly can this method generate energy? Just look at fresh water and sea water. Imagine on one side of a tank there is fresh water, and the other side houses sea water. The only thing standing between the two tanks is a semi-permeable membrane, which allows only water molecules to pass through. The sea water is going to naturally have a much higher salt concentrate than the fresh water, and that large difference will cause the molecules from the fresh water side to rapidly pass to the sea water side. This causes pressure that can be turned into electricity.
“The planet naturally makes salt water and fresh water, so we should take advantage of that,” says Herring, Vice Chair of ECS’s Energy Technology Division. “It’s free energy.”
Salt water computer
One researcher working in the field of blue energy is Taek Dong Chung, who presented his paper, “Reverse Electrodialysis for Unique Devices,” at the PRiME 2016 meeting. Chung’s work focuses on what he calls “iontronics” (conventionally referred to as ionics) to develop energy carriers for applications ranging from medical to water splitting for renewable energy; but it all starts with a computer powered by salt water.
“We’re working on finding a new way to use salt concentration in a water-based computer.” says Chung, a Seoul National University professor. “That means we’re developing a computer that is driven by salt in water.”
For this, Chung is applying iontronics, which functions similarly to the human nervous system.
Iontronics and medical applications
“We need a way to approach the human body with electrochemistry, and I think iontronics could be that way,” Chung says. “This allows us to interface between our nervous system and a computer or artificial system through a seamless device.”
Iontronics also draw many similarities to electronics, but instead of being driven by electrons, iontronics are driven by ions. However, the power tends to be much lower than that of conventional electronics, which makes them impractical for devices such as smartphones and computers. Because iontronics function on the same principals as the human nervous system and are able to emit low-powered electrical fields, Chung believes the real potential for this technology lies in patch-based drug delivery systems.
While these medical patches for drug delivery are not new, applying the iontronic technology would significantly reduce the delivery speed as well as make the overall experience safer for patients.
“By using the iontronics and the salt gradient, the power generated is very low but enough so that we can efficiently enhance drug delivery through the skin,” Chung says. “This way, we can successfully deliver drugs that would typically be ingested or invasively injected. The former methods often cause side effects, but this patch would be a much safer method of drug delivery.”
Think of Alzheimer’s disease, where memory loss and mental function dissipate as neurons in the brain die. While neurons cannot be revived, there are steps that can be taken to supplement artificial additives to help slow the effects of the disease.
“I think iontronic devices could one day be implanted in a brain as part of your body,” Chung says.
Future of water splitting
But potential applications don’t end with drug-delivery patches. Chung believes that his work in blue energy could mean big things for water splitting applications, potentially leading to the practical and efficient splitting of hydrogen and oxygen to produce energy.
Many researchers in the scientific community have been focusing on water splitting for its potential in renewable energy, but there have been barriers along the way.
“People want to use sunlight to generate hydrogen and oxygen. The problem is that it’s not easy to find the appropriate semiconductor that can harvest enough light and generate a high enough potential to split water,” Chung says. “People working on these devices are suffering from lack of candidates for semiconductors.”
By combining the current semiconductors used in these applications with a salt gradient power source, the necessary voltage could be achieved to do water splitting. Efficient water splitting techniques could open the door to solar fuels and potential shift the energy infrastructure.
Solving energy/water challenges
Blue energy is just the tip of the iceberg when it comes to the energy/water nexus. In other areas of the field, researchers are working on developing membranes for more efficient water treatment, creating electrochemical devices to recycle dangerous fertilizer runoff to prevent algae blooms, processing urine to produce clean water and hydrogen as a byproduct, and much more.
“There’s a lot of work to do and the issue is complicated,” Herring says. “But I know that the ECS scientists will end up making the awesome new materials and devices that solve all of these issues.”
