Influence of Water Solvation

Many experiments (especially electrochemical studies) are performed under wet conditions, and the presence of an electrolyte may change the overall energetics of gas phase reaction mechanisms. Of course, the ORR reaction creates water molecules as final reaction products. Eley-Rideal reaction mechanisms (which will be discussed in the next Section) also rely on the electrolyte as a source of hydrogen atoms. Although results from gas-phase calculations are sometimes used to interpret experiments performed in solution, we believe that at least some treatment of the water solvent is required to obtain relevant results. 

As mentioned earher in this chapter, solvation presents a formidable problem for theory. Simulations treating all surroimding water molecules explicitly with quantum chemical approaches would not even provide the most accurate results. Rather, molecular dynamics simulations updated with quantum chemical forces (via ab initio molecular dynamics) should provide 

On the dissociation pathway, formation of two 0 species is -1.71 eV downhill in solvent rather than -1.06 eV in gas phase. However, the barrier for this process hardly changes from 0.63 eV to only 0.68 eV. This is certainly due to the higher sol- 

On the 0011 formation pathway, the initial steps are again equivalent to the dissociation, but 00H formation is now 

22 eV uphill in solvent compared to -0.32 eV downhill in gas phase. The barrier to form 00H is greatly increased from 0.15 eV in gas phase to 0.94 eV in solvent. Here, water substantially destabilizes both the transition state and Water has little 

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