May 15, 2019 10:12 AM EDT
Collaborators from East China Normal University in Shanghai, Shanghai University, and the Chinese Research Academy of Environmental Sciences in Beijing, China have designed a new power generator inspired by marine organisms that switch from aerobic and anaerobic modes.
This research will benefit detectors, diving robots, and underwater vehicles that need their own energy supply to work independently from ships. The researchers developed a method that was able to direct electrochemical extraction of energy from seawater. The findings of their study were published in Angewandte Chemie.
Underwater devices are tasked to chart submarine landforms, temperatures, currents, and inspecting and repairing pipelines and deep-sea cables. These extreme conditions hinder the capacity of power generators as they have to produce a high power density (short-term high current flow) and a high energy density (long run time with basic power use).
The lead researchers are Liang Tang, Hu Jiang, and Ming Hu. They based their research on the principle of marine organisms that switch their cell respiration between aerobic and anaerobic modes.
"The key to the discovery is a cathode made of Prussian blue, an open framework structure with cyanide ions as "struts" and iron ions as "nodes", which can easily accept and release electrons. When combined with a metal anode, this structure can be used to generate electricity from seawater," according to the research.
Electrons that flow into the cathode are transferred directly to dissolved oxygen if there is small power demand. It is theoretical that there is inexhaustible dissolved oxygen in seawater. Thus, there is unlimited time for power at low current. The issue is that there is low dissolved oxygen concentration.
When the power demand, and thus current, are sharply increased, there is not enough oxygen at the cathode to immediately take up all of the incoming electrons. The Prussian blue must therefore store these electrons by reducing the oxidation state of the iron atoms from +3 to +2. To maintain a charge balance, positively charged sodium ions lodge within the framework. Because these are present in high concentration in seawater, many sodium ions-and therefore many electrons-can be absorbed in a short time. When the current demand slows down, electrons are transferred to oxygen once again, oxygen regenerates the framework, Fe(2+) is oxidized to Fe(3+), and the sodium ions depart.
There is high stability in corrosive seawater for the new system. It can adapt to numerous mode switches. The system was able to run in high-energy mode without losing power for four days and was able to provide power to a propeller and 39 light-emitting diodes.
This new system is very stable in corrosive seawater and can withstand numerous mode switches. It ran continuously for four days in its high-energy mode without losing power. The high-power mode was able to supply 39 light-emitting diodes and a propeller.
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