Electrocatalysis of the electroreduction of nitric acid by metals

The literature data on the electroreduction of nitric acid to hydroxylamine on various metals is analyzed as regards the electrocatalytic trends. In general moderate values of MH and MO bond energies, between the metal M and the anchoring group −H or −O (of −NO3), herald higher electrocatalytic activity; too low MH interaction energy or too high MO bond energy is associated with lower activity. Some volcano-type correlations between the MH or MO interaction energies and the electrocatalytic activities are observed for the transition metals whereas the sp metals do not show such relationships. It is further observed that the ability of the metal to electrocatalyze nitric acid reduction is roughly related to its exchange current density for the hydrogen evolution reaction. These correlations are interpreted on the basis of previous kinetic theory and some mechanistic proposals are put forward.