The research focused on carbon materials extracted from the electrodes of spent lithium-ion batteries (LIBs). The team employed an acidic leaching process to recover valuable metals from these electrodes. Depending on experimental conditions, the extracted carbon materials retained trace amounts of metals like cobalt, commonly used in catalysis. The goal was to repurpose these materials for use in catalytic processes, with a particular emphasis on hydrogen peroxide production.
"Hydrogen peroxide is one of the fundamental chemical molecules, essential to numerous industries. Large-scale production of this substance typically demands high pressures and temperatures, costly catalysts, and various toxic electrolytes. Our focus was on developing a more environmentally friendly method for producing hydrogen peroxide: specifically, an electrochemical approach using catalysts derived from used lithium-ion batteries," explains Dr. Eng. Magdalena Warczak (PBS), project leader and lead author.
The team's electrochemical tests demonstrated that carbon nanostructures and cobalt recovered from the batteries exhibited catalytic properties for the oxygen reduction reaction. However, these properties were influenced by the composition and structure of the sample, which were determined by the types of etching baths used to clean the extracted electrodes.
"For potential future applications, the crucial finding is that, based on data gathered from experiments using a rotating electrode, we were able to determine the number of electrons involved in the reduction of a single oxygen molecule. The electrochemical reduction of oxygen can occur with either four or two electrons. In the case of four electrons, water is produced, but with two electrons, we obtain the desired hydrogen peroxide. In all the samples we tested, we observed the two-electron reduction," explains Dr. Warczak.
To ensure accuracy, the measurements were repeated with battery powders suspended between two immiscible liquids, eliminating any influence from the glassy carbon electrode. The oxygen reduction reaction occurred spontaneously at the interface of these liquids, with the organic liquid containing decamethylferrocene, an electron donor. These experiments confirmed that all samples catalyzed the production of hydrogen peroxide, with concentrations measured by a scanning electrochemical microscope showing levels one to two orders of magnitude higher than those in systems without battery waste.
"Lithium-ion batteries have generally been viewed as just a secondary source of carbon materials, mainly graphite, and metals like lithium, cobalt, or nickel. Meanwhile, our group's findings clearly demonstrate that battery waste can catalyze the reduction of oxygen to hydrogen peroxide, and in the future, this could lead to its use in producing this important chemical compound," concludes Dr. Warczak.
Hydrogen peroxide, commonly found in pharmacies at a 3% concentration for disinfecting wounds, has a range of industrial applications. Solutions with up to 15% concentration are used in household cleaning products and cosmetics, while concentrations of around 30% are vital in industries such as chemical manufacturing, pulp and paper, textiles, electronics, and food processing. Hydrogen peroxide also serves as an oxidizer for fuels, including rocket propellants. During the 1940s, it was first used in early rockets capable of reaching space. Recently, hydrogen peroxide at concentrations exceeding 98% powered a suborbital rocket built by the Lukasiewicz Institute of Aviation in Warsaw.
The research on hydrogen peroxide production from spent lithium-ion batteries, initially funded by a SONATA grant from the Polish National Science Centre, will continue with a focus on enhancing the efficiency of electrochemical reactions for industrial use. The team also plans to explore four-electron reduction for potential applications in fuel cells.
Research Report:Insights into the High Catalytic Activity of Li-ion Battery Waste Toward Oxygen Reduction to Hydrogen Peroxide