The effects of choline chloride on the hydrogen evolution reaction, formic acid electrooxidation, and carbon dioxide conversion are investigated on a platinum cathode. We find that choline chloride suppresses hydrogen formation, but by contrast formic acid electrooxidation is enhanced and the overpotential of carbon dioxide reduction is reduced dramatically. We also find that choline chloride can be used to extend the window where electrochemical experiments can be performed. These results demonstrate that monolayers of species such as choline can have significant effects that need to be explored in more detail. (C) 2013 Elsevier Ltd. All rights reserved.