Zinc-air batteries get solar energy makeover

Solar energy. (Reference image by 18447309, Pixabay).

Researchers at the Korea Institute of Science and Technology (KIST) developed a technology to improve the electrochemical performance of zinc-air batteries by utilizing solar energy.

Zinc-air batteries, which produce electricity through a chemical reaction between oxygen in the atmosphere and zinc, are considered to be next-generation candidates to meet the explosive demand for electric vehicles instead of lithium-ion batteries.

The devices theoretically meet all required characteristics for next-generation secondary batteries, such as high energy density, low risk of explosion, eco-friendliness, and low cost of materials.

The battery developed at KITS utilizes a photoactive bifunctional air-electrocatalyst with a semiconductor structure with alternating energy levels, which significantly improves the rates of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) that generate electricity. The photoactive bifunctional catalyst is a compound that accelerates chemical reactions by absorbing light energy and has an improved light absorption ability than conventional zinc-air battery catalysts.

Zinc-air batteries get solar energy makeover
Schematic preparation and TEM images with elemental distributions in the red rectangle marked area for CZ.(Image courtesy of KITS).

In a zinc-air battery that uses metal and air as the anode and cathode of the battery, OER and ORR must be alternately performed for electrical energy conversion of oxygen as the cathode active material.

Therefore, the catalytic activity of the positive electrode current collector, made of carbon material, is an important factor in determining the energy density and overall cell efficiency of zinc-air batteries.

Accordingly, the research team focused on the p-n heterojunction, the basic structural unit of solar cells and semiconductors, as a measure to improve the slow catalytic activity of zinc-air batteries. The goal was to accelerate the oxygen production-reduction process by using the interface characteristics of semiconductors in which electron movement occurs. To this end, a cathode material with a heterojunction bandgap structure was synthesized, with an n-type semiconductor.

In addition, an experiment was conducted under real-world conditions without light in order to confirm the commercial potential of the photoactive bifunctional catalyst with a p-n heterojunction structure with alternating energy levels. The prototype battery showed an energy density of 731.9 mAh gZn-1, similar to the best performance of the existing zinc-air battery.

In the presence of sunlight, the energy density increased by about 7% up to 781.7 mAh gZn-1 and it showed an excellent cycle performance of 334 hours, 1,000 cycles, the best among known catalysts.

“Utilization of solar energy is an important part not only in improving the electrochemical performance of secondary batteries but also in realizing a sustainable society,” lead researcher Joong Kee Lee said in a media statement.

“We hope that this technology will become a catalyst that stimulates the development of new convergence technologies in semiconductor physics and electrochemistry, in addition to solving the difficulties of metal-air batteries that are emerging as an alternative to lithium-ion batteries.”