Different reaction routes in electrocatalytic nitrate/nitrite reduction using an H+-conducting solid polymer electrolyte

Electrocatalytic reduction of NO3-/NO2- in an aqueous solution was carried out over several bimetallic cathodes, which were deposited on a Nafion-117 H+-conducting polymer membrane. The reactivity and selectivity were largely dependent on metallic compositions of the cathode. In contrast to the inactive feature of Pt alone, the activity was significantly improved by the deposition of Ni, Cu, Ag and/or Rh onto Pt. Although the activity was enhanced mostly by Cu or Ag, their reaction mechanisms are quite different, i.e., the catalytic hydrogenation of nitrate (H2- NO3- reaction) occurs on the Cu–Pt cathode, whereas the Ag–Pt cathode exhibits an electrochemical route of nitrate reduction.