An artistic representation of the pH-gradient-enabled microscale bipolar interface (PMBI). The two layers that make up the interface are covering the third bottom layer, which is the electrode with palladium particles on it. The submarine and drones are envisioned applications of the direct borohydride fuel cell that incorporates the PMBI. (McKelvey School of Engineering)

While more people are using electric cars, designing electric-powered planes, ships, and submarines is much harder due to power and energy requirements. A high-power fuel cell was developed that uses a pH-gradient-enabled microscale bipolar interface (PMBI). The direct borohydride fuel cell operates at double the voltage of today’s commercial fuel cells.

The pH-gradient-enabled microscale bipolar interface runs the fuel cell with liquid reactants and products in submersibles, in which neutral buoyancy is critical, while also being used in higher-power applications such as drone flight. The fuel cell uses an acidic electrolyte at one electrode and an alkaline electrolyte at the other electrode. Typically, the acid and alkali will quickly react when brought in contact with each other. The PMBI is thinner than a strand of human hair so it can keep the acid and alkali from mixing, forming a sharp pH gradient and enabling the successful operation of the system.

Previous attempts to achieve this kind of acid-alkali separation were not able to synthesize and fully characterize the pH gradient across the PMBI. Using a novel electrode design in conjunction with electroanalytical techniques, the acid and alkali remain separated.

For more information, contact Leslie McCarthy at This email address is being protected from spambots. You need JavaScript enabled to view it.; 314-935-6603.


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This article first appeared in the September, 2021 issue of Tech Briefs Magazine.

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