The effect of ultra-low proton concentration on the electrocatalytic reduction of nitrate over platinum

The electrocatalytic reduction of NO3-(aq) over platinum has been investigated in sulfuric acid solutions with proton concentrations between 1 mM and 50 mM. Cyclic voltammetry indicates that for [H+] < 10 mM, NO3-(aq) is reduced in two distinct regions of potential: one reduction peak occurs at approximately 0.1 V vs. RHE and one occurs at −0.13 V vs. RHE. This second reduction peak has never before been observed, and is not present for proton concentrations >10 mM, where hydrogen electroreduction prevails below 0.0 V vs. RHE. Chronoamperometry shows that the kinetics of the two reduction peaks are distinct, suggesting that the two reduction peaks may correspond to the evolution of different products. Results are discussed in the context of tuning the product selectivity of the electrocatalytic reduction of NO3-(aq).