Enhanced electrocatalytic reduction of aqueous nitrate by modified copper catalyst through electrochemical deposition and annealing treatment

Copper has been intensively investigated as an electrocatalyst for electrochemical reduction of aqueous nitrate. Here we report preparation of Cu electrocatalyst by electrochemical deposition of Cu on Ni foils, annealing treatment to produce nanograins of Cu oxides and electroreduction to form metallic Cu nanograins to enhance the catalytic activities of nitrate reduction. The prepared Cu electrocatalysts were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The electrochemical deposition of Cu on Ni substrates produced different sizes and sharp-edged microcrystal of Cu, and the annealing treatment at 300°C transformed these microcrystals into uniform spheroids of Cu oxides in sizes of 150–350 nm. The potentiostatic electrolysis of aqueous nitrate showed that the annealing treatment improved nitrate reduction efficiency by 4.5 times and 20% at −0.8 and −1.4 V versus the saturated calomel electrode, respectively. The rate and Faradaic efficiency for nitrate reduction by modified Cu electrode remained constant within a testing time of 48 h. The results demonstrate that electrochemical deposition on Ni foils and subsequent annealing treatment provide a simple and cost-effective approach to enhance the catalytic activity and stability of a transition metal catalyst.