Electrochimica Acta 114 (2013) 813–818 Contents lists available at ScienceDirect Electrochimica Acta jo u r n al hom ep age: www.elsevier.com/locate/electacta Ni–Sn coatings as cathodes for hydrogen evolution in alkaline solutions B.M. Jovi ´ c a , U. ˇ C. Laˇ cnjevac a , N.V. Krstaji ´ c b , V.D. Jovi ´ c a,∗ a Institute for Multidisciplinary Research, University of Belgrade, P.O. Box 33, 11030 Belgrade, Serbia b Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia a r t i c l e i n f o Article history: Received 26 January 2013 Received in revised form 26 May 2013 Accepted 1 June 2013 Available online 19 June 2013 Keywords: Ni–Sn alloy Deposition EIS Roughness HER Chemical composition a b s t r a c t In this work the hydrogen evolution reaction (HER) at Ni–Sn alloy coatings, deposited onto Ni 40 mesh at different current densities from the bath containing 0.1 mol dm -3 SnCl 2 + 0.3 mol dm -3 NiCl 2 in the pyrophosphate–glycine solutions, was investigated by polarization and EIS measurements. The mor- phology and chemical compositions of all samples were investigated by the SEM and EDS techniques. It was shown that their morphologies and chemical compositions depend on the deposition current den- sity. The increase of their catalytic activity for the HER in 6 mol dm -3 KOH and in 1 mol dm -3 NaOH with increasing the deposition current density was shown to be the consequence of the change of both: their chemical composition and morphology. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction The alkaline water electrolysis is a well established process, technologically very simple, producing very clean H 2 and O 2 gases, but it is also energy inefficient, slow and expensive process [1]. In conventional water electrolysis cathodes are made either of stain- less steel or nickel-based materials and these systems operates in 20–25 wt.% KOH or NaOH solutions at temperatures between 70 ◦ C and 80 ◦ C [1]. The overall energy efficiency of electrolysis is related to the HER. Hence, for the industrial application advanced electro- catalytic materials for the HER are of great importance for energy efficiency. Several approaches to design and produce new elec- trocatalytic cathode materials were made in the past [2–11]. One of these approaches is based on the Brewer intermetallic bond- ing theory [2–4]. According to this theory better catalytic activity of cathodes can be achieved using expensive alloying procedures (such as a wire-arc spray or chemical vapor deposition techniques [5], electrochemical co-deposition of Ni with the transition metals (Mo, W) [6–8]), as well as in situ addition of ionic activators during the electrolytic hydrogen evolution [9–11]. Catalytic activity for the HER in alkaline solutions on elec- trodeposited Ni–Sn alloys has been first discovered in 1992 in the work of Santos et al. [12]. It was shown that such coatings ∗ Corresponding author. Tel.: +381 11 3303688; fax: +381 11 3055289. E-mail address: vladajovic@imsi.rs (V.D. Jovi ´ c). possess low overvoltage for hydrogen evolution in alkaline solu- tion, although the correlation between the characteristics of the alloys and the ability for the HER has not been discussed. In the work of Yamashita et al. [13] the influence of the electrodeposi- tion conditions (bath composition, temperature, current density, etc.) on the morphology of the Ni–Sn alloy coatings and over- voltage for the HER in alkaline solution has been investigated. By changing the deposition current density and concentration of SnCl 2 in the pyrophosphate–glycine bath, Ni content in the alloy coatings was changed from 34 to 99 at.%, while the overvoltage for hydrogen evolution was found to be practically independent of the alloy composition in the range 53–90 at.%. The morphology of the coatings was found to change from relatively smooth, fine grain structure, at low plating current density, to nodular one appearing as large spherical particles with the diameter of about 15 m at high plating current density [13]. In our previous work [14], Ni–Sn alloy coatings were electrodeposited onto Ni plate electrodes from the pyrophosphate–glycine bath containing the same concentra- tions of Sn 2+ and Ni 2+ ions (0.1 mol dm -3 ) at different current densities and their morphology, chemical and phase compositions were investigated. Four crystalline phases of low crystallinity were detected in total: face centered cubic (fcc) Ni phase, hexagonal close packed (hcp) Ni 3 Sn phase, hexagonal Ni (1+x) Sn (0 < x < 0.5) phase adopting NiAs type structure (dominant in most samples) [13,14] and monoclinic Ni 3 Sn 4 phase with CoSn type structure. Mainly Ni 3 Sn 4 phase (and in small amount Ni 3 Sn phase) were detected in the sample deposited at the lowest current density (-2 mA cm -2 ), 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.06.024