Development of CuNi immobilized Pt surface to minimize nitrite evolution during electrocatalytic nitrate reduction in neutral medium

Nitrite (NO₂⁻) is one of the major troublemakers in our environment, merits rigorous attention on removal purposes via effective treatments. Meanwhile, often NO₂⁻ ions are evolved as stable intermediates during electrocatalytic nitrate reduction reaction (NRR). In the present article, it is shown how the immobilization of Cu and Ni particles on a Pt surface influences both nitrate and nitrite reduction rates in the neutral medium. Using sandwich type membrane reactor, it was observed that NO₃⁻ and NO₂⁻ ions reduced having a first order rate constant (k) of 26.1×10^–3 min⁻¹ and 29.5×10^–3 min⁻¹, respectively at a Pt-CuNi cathode surface. Due to larger NO₂⁻reduction rate, NO₂⁻ ions did not appear while NO₃⁻ ions were reduced at the Pt-CuNi electrode surface. At the end of reaction, NH₃ was identified as the only product. Beside the evaluation of reactivity and product selectivity, several kinetic properties of NRR at Pt-CuNi surface were also evaluated. A Pt-Cu electrode requires 10.05 kJmol⁻¹ activation free energy, but this energy is decreased to 5.76 kJmol⁻¹ while Pt-CuNi electrode is used to attain NRR in the neutral medium. All the experimental data revealed that incorporation of Ni into Pt-Cu matrix, significantly improves NRR efficiency. In addition, the NRR process does not compete with hydrogen evolution reaction (HER) process at the Pt-CuNi electrode surface. Finally, Pt-CuNi being the efficient catalyst for attaining NRR, this catalyst was characterized with different electrochemical and spectroscopic techniques to unveil inherent physical properties.