Ni/Pd surfaces. The chain mechanism is significantly more favorable though the difference declines with decreasing potential. The 3H2O barrier could not be obtained on Pt due to its very large *OH binding energy. OH -(in solution) is more likely to be produced than *OH on a Pt surface, but the treatment of solvated OH -would require many more explicit water molecules. Explicit treatment of the electrochemical interface is relegated to our metadynamics studies of the Volmer reaction in the next section.