The Overpotential in Electrocatalytic Processes

Experimental data for the variation of the rate of the OER and ORR with potential for a number of materials are shown in Eigure 11.14. For all the electrocatalysts, the OER does not start to have an appreciable current density j until a substantial oveipotential 

FIGURE 11.14 Measured current density as a function of applied potential for the ORR and OER over different electrode catalysts. =E jj q,q =1.23 V is indicated. Adapted from Gorlin 

The previous examples can be generalized as follows. According to Equation (R11.4), we can write the free energy change for any elementary step, i, in an electrochemical reaction with a transfer of one electron and a proton as 

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