Electrochemically Activated Copper Electrodes Surface Characterization, Electrochemical Behavior, and Properties for the Electroreduction of Nitrate

A polycrystalline copper electrode was activated by creating a nanostructured and highly electrocatalytic surface through an appropriate electrochemical treatment in 1 M NaOH. It was demonstrated that a thick layer (∼2 μm) of Cu(OH) 2 nanoneedles can be formed on copper substrate after 3000 cycles (scan rate 10 V s -1 ) between -1650 and 1000 mV vs Hg/HgO or by anodization for 15 min at -100 mV. Energy dispersive X-ray analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and in situ Raman spectroscopy analyses revealed that the conversion of orthorhombic Cu(OH) 2 to face-centered-cubic Cu is completed after 20 cycles between -450 and -1650 mV at 20 mV s -1 . However, copper obtained from the reduction of the thickest Cu(OH) 2 nanoneedle films formed by a repetitive fast cycling or by anodization at -100 mV appeared as nanowires, whereas the electrode anodized at 0 or 700 mV recovered a quasi-smooth original copper surface. The presence of high-energy sites on these Cu nanostructures was highlighted by cyclic voltammetry in the pseudo-capacitive potential region, where premonolayer oxidation was observed with an unusually high magnitude at unusually low potentials. As a result, a remarkable improvement of the electrocatalytic activity of the activated Cu electrodes for the nitrate electroreduction was observed.

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