Electrochimica Acta 56 (2010) 154–165 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Electroreduction of nitrate ions on Pt(1 1 1) electrodes modified by copper adatoms E.B. Molodkina a , M.R. Ehrenburg a , Yu.M. Polukarov a , A.I. Danilov a,∗ , J. Souza-Garcia b , J.M. Feliu b a A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russia b Institute of Electrochemistry, University of Alicante, Alicante, Spain article info Article history: Received 25 June 2010 Received in revised form 23 August 2010 Accepted 24 August 2010 Available online 17 September 2010 Keywords: Nitrate reduction Pt(1 1 1) Cu-modified electrodes abstract Kinetics and mechanism of nitrate ion reduction on Pt(1 1 1) and Cu-modified Pt(1 1 1) electrodes have been studied by means of cyclic voltammetry, potentiostatic current transient technique and in situ FTIRS in solutions of perchloric and sulphuric acids to elucidate the role of the background anion. Modification of platinum surface with copper adatoms or small amount of 3D-Cu crystallites was performed using potential cycling between 0.05 and 0.3 V in solutions with low concentration of copper ions, this allowed us to vary coverage  Cu smoothly. Following desorption of copper during the potential sweep from 0.3 to 1.0 V allowed us to estimate actual coverage of Pt surface with Cu adatoms. Another manner of the modification was also applied: copper was electrochemically deposited at several constant potentials in solutions containing 10 -5 or 10 -4 M Cu 2+ and 5 mM NaNO 3 with registration of current transients of copper deposition and nitrate reduction. It has been found that nitrate reduction at the Pt(1 1 1) surface modified by copper adatoms in sul- phuric acid solutions is hindered as compared to pure platinum due to induced sulphate adsorption at E < 0.3 V. Sulphate blocks the adsorption sites on the platinum surface and/or islands of epitaxial Cu(1 × 1) monolayer thus hindering the adsorption of nitrate anions and their reduction. The extent of inhibition weakly depends on the copper adatom coverage. Deposition of a small amount of bulk copper does not affect noticeably the rate of nitrate reduction. Nitrate reduction on copper-modified Pt(1 1 1) electrodes in perchloric acid solutions occurs much faster as compared to pure platinum. The steady-state currents are higher by 4 and 2 orders of magnitude at the potentials of 0.12 and 0.3 V, respectively. The catalytic effect of copper adatoms is largely caused by the facilitation of nitrate adsorption on the platinum surface near Cu ad and/or on the islands of the Cu(1 × 1) monolayer (induced nitrate adsorption). Hydrogen adatoms block the adsorption sites on platinum for NO 3 - anion adsorption and inhibit reactions of nitrate reduction even at moderate surface coverage. The products of nitrate reduction in sulphuric and perchloric acids are essentially the same (NO and ammonia) irrespective of the presence or absence of Cu on the platinum surface. Crown Copyright © 2010 Published by Elsevier Ltd. All rights reserved. 1. Introduction Kinetics and mechanism of nitrate ion reduction on plat- inum have been studied for many decades ([1–10] and references therein). Nitrate reduction allows obtaining nitrous oxide used as an anesthetic in medical practice, ammonia, hydroxylamine, and other nitro-compounds. Besides, there is a problem of nitrate removal from effluent water and nuclear waste. One of the most environmentally safe and selective methods appears to be electro- ∗ Corresponding author at: Frumkin Institute of Physical Chemistry and Electro- chemistry, Leninskii prospekt 31, 119991 Moscow, Russia. Tel.: +7 495 955 44 56; fax: +7 495 952 53 08. E-mail address: danilov@phyche.ac.ru (A.I. Danilov). chemical reduction of nitrates. This reaction was studied at noble and transition metals (Pt, Ir, Rh, Ru, Pd, Au, Ag, Cu, Zn, Ni, Pb, Fe), alloys, and electrodes modified by adatoms of copper, lead, tin, germanium, etc. [5,7,8,10–17]. The majority of these studies were carried out on polycrystalline electrodes. There are only a few papers devoted to investigation of nitrate reduction on basal faces and stepped surfaces of platinum and copper single crystals [18–24]. Summarizing the results of these studies it should be noted that the reduction mechanism depends on the nitrate concentra- tion, electrode material, nature of the anion in background solution, acidity, electrode potential, and presence of molecular or cationic additives. Multi-step discharge of NO 3 - ions is accompanied by for- mation of intermediates of different stability and adsorption ability. Key reaction products in acidic solutions are N 2 O, N 2 , NH 4 + , and 0013-4686/$ – see front matter. Crown Copyright © 2010 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2010.08.105