Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2003, 42 (31), 3653-3655
Economical and Explosion-free
A new fuel-cell concept for the catalytic production of hydrogen peroxide
Hydrogen peroxide (H2O2) is an important industrial reagent, which is used in such processes as the environmentally friendly bleaching of paper and wastewater treatment. Current industrial methods for the bulk production of H2O2 are expensive, both in terms of energy and cost. A new method developed by Japanese researchers could form the basis of a new, substantially more economical process.
Ichiro Yamanaka's team has been working on the catalytic conversion of hydrogen and oxygen into hydrogen peroxide. A mixture of hydrogen and oxygen is highly explosive. Yamanaka and his co-workers thus chose a method that guarantees a controlled reaction, even though the two volatile reactants never come into direct contact: electrocatalytic conversion in a fuel cell. The special advantage of this concept is that the energy released in the reaction can be captured in the form of an electric current. The researchers have now further improved their original fuel cell concept.
The secret of their success is a three-phase interface within the cathode, the negative electrode. Rather than introducing oxygen in an electrolyte solution, as was done previously, a stream of oxygen gas is introduced directly onto the solid, but porous, cathode. The other side of the cathode contains a dilute sodium hydroxide solution as an electrolyte, which also enters the pores. This allows for higher oxygen concentration on the inner electrode surface, allowing in turn for a higher conversion. Hydrogen gas is directed in a similar way onto the equally porous anode.
A further crucial improvement lies in the enclosure of the electrolyte solution within cathode and anode areas by a semipermeable membrane. This solves another problem that plagued the previous version of the fuel cell; the hydrogen peroxide formed at the cathode no longer has access to the anode, where it would decompose to form water. Last but not least, the efficacy of the catalytic graphite electrodes was increased by the inclusion of various additives.
Even when air is used in place of pure—expensive—oxygen, the output of the fuel cell is high enough. This renders the concept an economically interesting alternative for the bulk production of hydrogen peroxide.