Acid and Alkaline Hydrogen-Bromine Fuel Cell Systems for Electrical Energy Storage

Comparison of Acid and Alkaline Hydrogen-Bromine Fuel Cell Systems

 

Trung Van Nguyen^a*, Venkata Yarlagadda^a, Guangyu Lin^b, Guoming Weng^c, Vanessa Li^c, and Kwong-Yu Chan^c

^aDepartment of Chemical & Petroleum Engineering

The University of Kansas

Lawrence, KS, USA

^bTVN Systems, Inc.

Lawrence, KS, USA

^cDepartment of Chemistry

The University of Hong Kong

Hong Kong SAR, China

^*Corresponding Author: cptvn@ku.edu

 

Abstract

The hydrogen bromine (H₂-Br₂) fuel cell system is an attractive system for electrical energy storage because of its high round-trip conversion efficiency, high power density capability, and anticipated low costs.

The hydrogen-bromine fuel cell system can be operated in the acid or alkaline modes. The charge and discharge electrode reactions in an acid H₂-Br₂ fuel cell system are as follows:

Bromine Electrode:

Br_{2 (aq)} + 2e- ↔ 2Br^-_(aq), E^o = +1.09 V

Hydrogen Electrode:

H_{2 (g)} ↔ 2H⁺ _(aq) + 2e-, E^o = +0.0 V

The H⁺ ions migrate from the hydrogen side across a proton conducting membrane to the bromine side during discharge to combine with the Br^- ions to form hydrobromic acid.

Overall Reaction:

H_{2 (g)} + Br_{2 (aq)} ↔ 2HBr _(aq), E^o = +1.09 V

The charge and discharge electrode reactions in an alkaline H₂-Br₂ fuel cell system are as follows:

Bromine Electrode:

Br_{2 (aq)} + 2e- ↔ 2Br^- _(aq), E^o = +1.09 V

Hydrogen Electrode:

H_{2 (g)} + 2OH^- _(aq) ↔ 2H₂O + 2e-, E^o = +0.83 V

The cations (e.g., K⁺), associated with the OH^- ions, migrate from the hydrogen electrode across a cation (K⁺) conducting membrane to the bromine side and combine with the Br^- ions to form KBr as shown in the overall reaction.

Overall Reaction:

H_{2 (g)} + Br_{2 (aq)} + 2KOH _(aq) ↔ 2H₂O + 2KBr _(aq),    E^o = +1.92 V

Based on the reactions shown above the alkaline system offers higher cell voltage, which is an advantage because of potentially higher power output. However, the hydrogen reactions in this system are two-phase reactions involving gaseous hydrogen and liquid-phase hydroxide ion reactants and will require more complex electrode structure and fuel cell design. The other advantages of this system include the fact that non-noble catalysts can be used for the hydrogen actions and lower corrosiveness.

This presentation will discuss the advantages and disadvantages of the alkaline and acid H₂-Br₂ fuel cell systems and compare the discharge and charge performance of both systems.

Acknowledgements

This work was funded in part by the National Science Foundation through grant number EFRI-1038234 and the Research Grants Council of Hong Kong through a General Research Fund (GRF HKU 700210P). A Visiting Professorship to Trung Nguyen was provided by the Initiative on Clean Energy and Environment (ICEE), University of Hong Kong.