Open circuit voltage hydrogen oxidation reaction

This mixed potential is explained in Fig. 5 through an Evans diagram. In an operating fuel cell, along with this polarization close to open circuit voltage (OCV), there are losses due to hydrogen permeation into cathode electrode from anode chambers in PEMFC and methanol crossover in direct methanol fuel cell (DMFC). In a half-cell system, the crossover losses do not exist, but the polarization due to the carbon oxidation or any other contaminant participating in a side-reaction depresses the OCV. 

As shown in Figure 3, the open-circuit potential represents the highest voltage obtainable for a single cell. This potential is derived from thermodynamics. The overall fuel-cell reaction can be broken down into the two global electrode reactions. If hydrogen is the primary fuel, it oxidizes at the anode according to the reaction... 

The standard negative electrode voltage on open circuit is Eq - —0.358 V when measured versus a standard hydrogen electrode. During discharge, lead (Pb) oxidizes by reacting with the bisulfate ion and loses two electrons to form lead sulfate (PbS04). The reaction is [4]... 

There is a minus sign in Eq. (2.19) since both half-cell reactions are taken as reduction reactions whereas Eq. (2.18) uses one reduction and one oxidation reaction. At standard conditions (pure oxygen and hydrogen, 1 atm pressure, and 298 K), we expect an open-circuit cell voltage of 1.23 V. 

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