Nitrate reduction in alkaline solutions mediated by Cu and Cd underpotential deposition on Au and Ni substrates

The behavior of Au and Ni electrodes, modified by underpotential deposition (UPD) of Cu and Cd, in correlation with the reaction of nitrate ion reduction in alkaline solution (0.1 M NaOH), was studied using the cyclic voltammetry method. Nitrate reduction on Au and Ni electrodes is superposed over the hydrogen evolution reaction (HER). Cu and Cd, presenting a high polarisation for HER, permit the obtaining of distinct waves for nitrate reduction in alkaline media. The gold electrode, modified by UPD Cu and Cd, has a similar behavior. The increasing of the nitrate reduction currents on Au/ UPD Cu and Au /UPD Cd, together with the underpotential shift in the negative direction - which corresponds to a large quantity of underpotential deposited metal - indicates catalytic properties for both electrodes. Underpotential deposition of Cu on Ni substrate is not accompanied by obtaining of distinct wave for nitrate reduction. The UPD Cu has an inhibitor effect on the global reaction; the current values decrease for the same polarisation, in comparison with the Ni electrode. It is possible that this effect of inhibition may be exerted only on the HER, by increase of its polarisation.