Fabrication of hydrazine sensor based on silica-coated Fe2O3 magnetic nanoparticles prepared by a rapid microwave irradiation method View project Electrochemistry of arsenic and hydrogen peroxide View project Copper-immobilized platinum electrocatalyst fo

Abstract

The electrocatalytic reduction of NO 3 − and its intermediate NO 2 − in neutral medium was performed at a Cu-immobilized Pt surface. The voltammetric investigations showed that the bare Cu electrode has little effect on nitrate reduction reactions (NRR) whereas an enhanced catalytic effect (i.e. a positive shift of the peak potential and an increased reduction current) was observed when Cu particles were immobilized onto Pt surface. At the Cu-Pt electrode surface, the NRR process was observed to occur via a two-step reduction mechanism with a transfer of 2 and 6 electrons in the first and second steps, respectively. Similar results were obtained by chronoamperometric (CA) studies. Closer NRR mechanistic studies at the as prepared Cu-Pt electrode revealed concentration-dependent kinetics with a "critical" nitrate ion concentration of ca. 0.02 M. Moreover, NRR proceeded via a simple adsorption-desorption mechanism following a Langmuir isotherm with an adsorption Gibbs free-energy of ca. −10.16 kJ mol −1 (1st step) and ca. −10.05 kJ mol −1 (2nd step). By means of a Pt|Nafion|Cu-Pt type reactor without any supporting electrolyte, bulk electrolysis was performed to identify nitrate reduction products. It was found that after 180 min of electrolysis, 51% of NO 3 − was converted into NO 2 − intermediate. This percentage decreased to 30% in CO 2 buffered conditions. However, when a tri-metallic Pt-Pd-Cu electrode was employed as a cathode, all of the NO 2 − produced could be successfully converted into NH 3 and N 2. The electrocatalysis of nitrate ion on Cu-Pt electrode surface showed no apparent surface poisoning as confirmed by its stability after excessive CV runs. This was further supported by surface analysis and morphology of the as-prepared catalyst with scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis.