1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 z Catalysis Surfactant-AssistedElectrodepositionofNickel NanostructuresandTheirElectrocatalyticActivitiesToward OxidationofSodiumBorohydride,Ethanol,andMethanol Mahdieh Zolfaghari, Ali Arab,* and Alireza Asghari [a] Different Ni nanostructures were electrodeposited from the Watts bath in the presence of different concentrations of sodium dodecyl sulfate (SDS) using the pulse reverse current technique on the copper substrate. The concentration of SDS was lower than the critical micelle concentration (CMC), equal to CMC and higher than CMC for electrodeposition of Ni-1, Ni- 2, and Ni-3 samples respectively. The electrodeposited samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission-scanning electron micro- scopy (FE-SEM) techniques. The electrocatalytic activity of samples for oxidation of sodium borohydride, ethanol, and methanol was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). For borohydride oxidation, one oxidation peak, as well as one semicircle, observed respectively in the cyclic voltammograms and Nyquist diagrams confirmed that only one reaction happened on the surface of samples. It was observed that at high overpotentials, Ni-1 sample was more reactive for NaBH 4 oxidation compared to the Ni-2 and Ni-3 samples. Introduction In recent years, the tendency to produce nano structures by electrodeposition has increased because of their unique properties. [1–2] Electrodeposition of nano crystalline nickel and its alloys has been the subject of many studies because of their various physical characteristics such as hardness, coating uniformity and corrosion resistance. [3–6] The surface morphology of electrodeposits was shown to be dependent on several parameters such as deposition over potential, current pulse modes, substrate material, and its surface properties, nickel ion concentration, chloride ions, and pH of the solution. [7–15] Nasirpouri et al. used three methods including pulse current (PC), pulse reverse current (PRC), and direct current (DC) for Ni electrodeposition. [16] They reported that electrodeposition con- ditions affect microstructure, cathodic efficiency, micro-hard- ness, and magnetic and corrosion properties of nickel films. Borkar et al. have reported that electrodeposition of nickel with PC and PRC methods reduces the grain size and surface roughness of films compared to the DC method. [17] Uniform dispersion of particles in the electrolytes can increase their participation in the coating and improve the coating properties. In this regard, various physical and chemical methods have been employed. Physical techniques, such as ultrasonic waves can break down the nano-particles bonding and inhibit the agglomeration. [18] In the chemical techniques, surfactants are attached to the surface of nano-particles. The presence of surfactants, which increase the repulsion force between particles with the same charges, reduces the agglom- eration and provides a solution with more stable particles. [2,19] Surfactants were used abundantly in the electrodeposition baths in order to obtain coatings with various properties. For example, Sabri et al. studied the effects of SDS concentration on the micro-hardness of nickel-alumina nano-composite coat- ings electrodeposited from nickel sulphamate solution contain- ing nano-alumina particles by direct current (DC) plating. [2] Kilic et al. used a nickel sulfate bath containing CTAB surfactant and SiC nanoparticles to obtain SiC nanoparticle-reinforced Ni metal matrix composites. They investigated the effect of CTAB concentration on the particle distribution, micro-hardness, and wear resistance of nano-composite coatings. [20] Elansezhian et al. prepared Ni P deposits in the presence of SDS and CTAB surfactants with different concentrations. They reported that the surface morphology and surface roughness of the deposits significantly depend on the surfactant concentration. [21] The electro-oxidation of ethanol and methanol, which occur at the anode of a direct alcohol fuel cell (DAFC), are the vital reactions. For a more efficient DAFC, higher power density and fuel utilization should be attained. For this purpose, both reaction kinetics and selectivity should be improved. [22] Direct borohydride fuel cell (DBFC) has been widely investigated as one of the most promising power sources because of their high energy density, high cell voltage, high hydrogen contents, high chemical stability in alkaline solution, low pollution, non-CO 2 emission, and non- flammable and easy handling. [23–25] The complete electro-oxidation of BH 4  generates 8 electrons according to Eq.(1). However, incomplete oxidation and hydrolysis of BH 4  in alkaline solution as presented by Eqs. 2 and 3, respectively, lead to a significant reduction in the utilization of BH 4  . [25] Therefore, it is necessary to [a] M. Zolfaghari, Dr. A. Arab, Dr. A. Asghari Department of Chemistry, Semnan University, P.O. Box. 35131–19111, Semnan, Iran Tel.: + 982331533195 Fax: + 982333654110. E-mail: a.arab@semnan.ac.ir Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201900345 FullPapers DOI:10.1002/slct.201900345 4487 ChemistrySelect 2019, 4, 4487 – 4495 © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim