A prototype of the water-based battery is only three inches tall and capable of producing 20 milliwatts of electricity per hour. Despite its current small size and weak power-generating capacity, the researchers believe their device will scale up in the future and will reach industrial scale, enabling it to be cycled up to 10,000 times. "We put special salts in water, put them into electrodes, and a reversible chemical reaction occurs, storing electrons in the form of hydrogen," said study coordinator Yi Cui.
Scientists use industrial salts used in the production of dry batteries, fertilizers, paper and other products to perform a reversible exchange of electrons between water and manganese sulfate. The incoming electrons react with the manganese sulfate dissolved in the water, causing the manganese dioxide particles to attach to the electrodes, and the excess electrons that appear are turned into hydrogen, which stores this energy for future use.
Next, the scientists reconnected the power source and the depleted device to ensure the battery could be charged. Manganese dioxide particles stick to the electrodes and combine with water, thereby replenishing the manganese sulfate salt. "Once the salt is recovered, incoming electrons become redundant, and the excess energy is released like hydrogen, a process that can be repeated over and over again.
The research team also said that a cheaper process that combines manganese sulfate and water is currently being developed.