Quantification of Voltage Loss in the PEM Reactor for Electrolyzing Hydrogen Bromide to Produce Hydrogen

Simultaneous conversion of gaseous hydrogen bromide to bromine and hydrogen can be accomplished in a Proton Exchange Membrane (PEM) electrolyzer. The cell voltage required to carry out this conversion is a function of design and operating conditions. The cell voltage is composed of the equilibrium cell potential as well as individual potential losses in the cell (e. g. ohmic, activation, mass transfer etc). All these potential contributions are greatly influenced by the water content in the membrane and at the catalytic surface. Therefore, it is necessary to accurately predict the water transport across the cell to quantify the individual voltage losses. The equilibrium cell potential is predicted by Nernst equation coupled with vapor-liquid equilibrium (VLE) calculations for the Br-2-HBr-H2O and H-2-H2O system. The model for predicting the total cell potential shows good agreement to the data over a range of current densities.