Electrochimica Acta 114 (2013) 215–222 Contents lists available at ScienceDirect Electrochimica Acta jo u r n al hom ep age: www.elsevier.com/locate/electacta Investigation of the porous nanostructured Cu/Ni/AuNi electrode for sodium borohydride electrooxidation Mir Ghasem Hosseini a,∗ , Mehdi Abdolmaleki a , Farzad Nasirpouri b a Electrochemistry Research Laboratory, Department of Physical Chemistry, Chemistry Faculty, University of Tabriz, Tabriz 0098 5166616471, Iran b Department of Materials Engineering, Sahand University of Technology, Tabriz, Iran a r t i c l e i n f o Article history: Received 16 July 2013 Received in revised form 28 September 2013 Accepted 3 October 2013 Available online xxx Keywords: Borohydride electrooxidation Electrocatalyst Galvanic replacement Cyclic voltammetry Direct borohydride fuel cell Electrochemical impedance spectroscopy a b s t r a c t An electrochemical approach to nanostructured Cu/Ni/AuNi catalyst design using the electrodeposition process followed by galvanic replacement technique is presented. The procedure consisted of the elec- trodeposition of Ni–Zn on the Ni coating with subsequent replacement of the zinc by gold at open circuit potential in a gold containing alkaline solution. The surface morphologies and compositions of coatings were determined by energy dispersive X-ray and scanning electron microscopy techniques. The results showed that the Cu/Ni/AuNi coatings were porous composing of discrete Au nanoparticles. The electro- catalytic activity of Cu/Ni/AuNi electrodes for sodium borohydride electro-oxidation was studied using cyclic voltammetry, chronoamperometry, chronopotentiometry and electrochemical impedance spec- troscopy techniques. The electro-oxidation current on Cu/Ni/AuNi catalyst is much higher than that on flat Au catalyst. The onset potential and peak potential on Cu/Ni/AuNi catalysts are more negative than that on flat Au catalyst for borohydride electrooxidation. The impedance behavior also shows different patterns, capacitive, and negative resistances and inductive loops at different applied anodic potentials. All results show that the Cu/Ni/AuNi catalysts can be applied as potential anode catalysts for the direct borohydride fuel cells. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction The increasing demand for efficient and clean power sources has greatly stimulated the research and development of low- temperature fuel cells for stationary and mobile applications [1,2]. Several promising fuels, e.g. hydrogen and methanol, have been intensively evaluated and concerns in poisoning, supply and stor- age, capacity and efficiency, toxicity were raised [1–4]. In recent years, aqueous solution of sodium borohydride has been widely studied as fuel in direct borohydride fuel cell (DBFC). The fuel (boro- hydride salt), also presents several advantages: it is non-toxic, can easily be stored and relatively stable in alkaline solution, while exhibits rather high energy density (9.3 Wh g -1 at 1.64 V) [5–8]. Borohydride fuel cells are currently under active investigation as part of worldwide efforts to develop environmentally sustainable sources of power [7–12]. The oxidation reaction of borohydride can take place with an eight-electron process described as follows (Eq. (1)) [13]: BH 4 - + 8OH - → BO 2 - + 6H 2 O + 8e - E 0 = -1.24 Vvs.SHE (1) ∗ Corresponding author. Tel.: +98 4113393138; fax: +98 4113340191. E-mail address: mg-hosseini@tabrizu.ac.ir (M.G. Hosseini). However, this reaction is barely found to happen in practice because the anodic reactions on the electrodes have to compete with the hydrolysis reaction. The hydrolysis of borohydride ion produces hydrogen gas and a number of borohydroxide or oxide intermediates that deplete the amount of borohydride ions avail- able for oxidation (Eq. (2)) [14,15]. BH 4 - + yH 2 O → BH 4-y - (OH) y + yH 2 (y = 1–4) (2) The electrochemical reaction of borohydride depends on the catalysts material, alkaline solution concentration and also on tem- perature. Pt- or Au-based binary electrocatalysts tested in reactions rel- evant to fuel cell technology (oxygen reduction [16,17]; methanol oxidation [18,19]; borohydride oxidation [20]) constitute a large part of recent electrochemical literature. The galvanic replacement procedure provides a very simple and effective method to prepare porous bimetallic nanostructures hav- ing a lower standard electrode potential compared to that of the target material. In this work, we demonstrate a procedure for synthesizing porous Cu/Ni/AuNi nanostructures via galvanic exchange reaction using Zn from Cu/Ni/ZnNi coating. NiZn coating was grown on Ni by electrodeposition technique and Cu/Ni/ZnNi electrode was obtained. Porous Cu/Ni/AuNi nanostructures were produced by exposing the Cu/Ni/ZnNi electrode to an alkaline aqueous solution 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.10.012