The molecular workings of a promising fuel cell electrolyte have been unraveled by chemists. A team of investigators from the New York University and the Max Planck Institute (Stuttgart) have revealed how protons migrate in phosphoric acid (H3PO4), a mineral acid, in a study published in Nature Chemistry. A mystery has always surrounded the understanding of how phosphoric acid is so efficient in proton conductivity.
The pioneering modern fuel cell types for commercial use owe their application to phosphoric acid fuel cells. These fuel cells have played a big role as both stationary and automotive power generation sources. They still make themselves remarkable targets for further development owing to their high efficiency as power and heat generators.
In the cell, the mineral (or inorganic) phosphorous acid functions as the electrolyte (or electricity conductor) that transports protons generated in the fuel decomposition reaction across the cell. The acid is renowned for its high proton conductivity over any other known substance.
For more than 200 years, chemists have done research work seeking to have a molecular understanding of the phenomena of proton conduction. History documents a landmark paper on the earliest studies involving water as an electrolyte by Theodor von Grotthuss, a German chemist. In this particular paper, Grotthuss suggested that the transport involves the chemical hydrogen bonding patterns of excess protons in aqueous acids through a series of minute proton hops between water molecules neighboring each other.
The Nature Chemistry study explained how a step-wise mechanism that involves hydrogen bonding patterns in aqueous phosphoric acid operates to achieve “streamlined” transfer of protons. They documented that there are steady sequential patterns of bond making and bond breaking instances. These form temporary wire arrangements which pass on protons between adjacent acid molecules leading to high conductivity.
The understanding of how the proton transport mechanism works is important in leading to designs of phosphate materials in fuel cell manufacturing. Notwithstanding, as pure power sources, phosphoric acid cells may not be as applicable as other cell types.