Germany: Research Solar Power to Chemicals: New Electrolytic Cell Produces Hydrogen Peroxide using Surplus Renewable Energy
In order to balance out spikes in power grids resulting from non-uniform regenerative energy conversion from wind or sun, surplus power can be used for the decentralized production of chemicals. German research center Fraunhofer IGB has developed an electrolytic cell in which hydrogen peroxide can be produced on site with electric energy from just water and air – along with oxidative wastewater treatment.
Wood-colored pulp from which white paper is to be produced, objectionable tooth discolorations or disinfecting work areas in hospitals and food production facilities: Due to its highly oxidizing and cell toxic effects hydrogen peroxide is widely used as a bleaching agent and disinfectant in many technical areas, the production of cosmetics and medical applications. Hydrogen peroxide has also become firmly established in oxidative water treatment. Here, under the influence of ultraviolet light, hydrogen peroxide forms hydroxyl radicals: these destroy organic molecules that are not easily biodegradable.
For the most part hydrogen peroxide is produced on a large scale in centralized chemical plants, generally from oxygen and hydrogen and with a catalyst made of expensive platinum. As hydrogen peroxide can decompose spontaneously in highly concentrated solutions and explode, it can only be transported as a hazardous substance subject to strict safety precautions. This substantially increases the transport costs.
The Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB has developed and implemented a new technical concept where hydrogen peroxide is generated locally and on the basis of demand in an electrochemical cell, that means with electricity alone – just from air and water. As a result of the turnaround in energy policy, there are non-uniform spikes in current supply from the regenerative production of energy. Thus the electrolytic production of chemicals is both becoming cost-effective and represents – in addition to the storage of energy – a practical utilization pathway for balancing out spikes in current supply to the grid.
Flexible synthesis in an electrolytic cell
The centerpiece of the development is a flat electrolytic cell. When an electric current flows, water is oxidized at the anode: protons are created and the pH value decreases. At the same time, atmospheric oxygen is reduced at the cathode, a gas diffusion electrode, which is also used for example in fuel cells. As a result, the protons are consumed and hydrogen peroxide is generated.
In a first demonstrator with 100 square centimeters of electrode area the researchers achieved concentrations of more than 400 milligrams hydrogen peroxide per liter when pure oxygen was supplied; when operating with ambient air as the source of oxygen, concentrations of 50 milligrams hydrogen peroxide per liter were obtained – with an energy requirement of 10 kWh/kg H2O2. Dr. Thomas Scherer, Group Manager at Fraunhofer IGB summarizes: “In the meantime we have further optimized the system. We were able to increase the yield from 50 milligrams to 1200 milligrams hydrogen peroxide per liter when operating with air and thus achieved the same turnover as when operating with pure oxygen.”