Nitrate Electroreduction Activation on Platinum

Nitrate electroreduction on Pt(111) and Pt(100) cannot evolve from bidentate adsorbed nitrate perpendicular to the surface, as it is generally assumed, because the only plausible next step in the mechanism, a proton-coupled electron transfer (PCET), invariably results in its desorption as nitric acid.However, nitrate can also be adsorbed on platinum in a tridentate configuration parallel to the surface, involving the nitrogen atom, although only on Pt(100).From this tridentate state, one of the surface-bound oxygen groups can be favorably cleaved from nitrate either before or after a PCET.By focusing on triatomic active sites and nitrogen instead of oxygen as a key requirement for activation, and by exposing the competition between nitrate adsorption modes, these results allow deriving catalyst optimization strategies.