Electrochimica Acta 115 (2014) 46–55 Contents lists available at ScienceDirect Electrochimica Acta jou rn al hom ep age: www.elsevier.com/locate/elec tacta Staircase and pulse potential electrochemical techniques for the facile and rapid synthesis of Pt and PtAg materials N. Arjona a,1 , M. Guerra-Balcázar b,1,2 , G. Trejo a,1 , L. Álvarez-Contreras c , J. Ledesma-García b,1 , L.G. Arriaga a,∗,1 a Centro de Investigación y Desarrollo Tecnológico en Electroquímica, 76703 QA, Pedro Escobedo, Mexico b División de Investigación y Posgrado, Facultad de Ingeniería, Universidad Autónoma de Querétaro, 76010 QA, Mexico c Centro de Investigación en Materiales Avanzados, Complejo Industrial Chihuahua, 31109 CI, Mexico a r t i c l e i n f o Article history: Received 8 August 2013 Received in revised form 16 October 2013 Accepted 17 October 2013 Available online 28 October 2013 Keywords: Electrochemical synthesis Cubic-shaped PtAg Platinum dendritic growth a b s t r a c t Electrochemical synthesis is an attractive option for the synthesis of materials because electrocrystal- lization is faster (microseconds), easier (fewer variables influence structure) and more cost-effective (only requiring an ion source and electrolyte) than traditional chemical methods. Pt and PtAg materials were synthesised using electrochemical techniques, including staircase cyclic voltammetry (CV). Differ- ential pulse amperometry (DPA), square wave voltammetry (SWV) and second harmonic AC voltammetry (2nd H AC V) were employed as pulse potential techniques. Characterisation was conducted using X-ray diffraction, field emission scanning electron microscopy, X-ray fluorescence, cyclic voltammetry in acidic and basic media and by assessing the behaviour of the synthesised materials in oxygen reduction reaction (ORR). For the cyclic voltammetry and DPA techniques, a decrease in the interfacial electrode/solution concentration resulted in the formation of semi-spherical nanoparticles with dendritic nanosheet growth. Semi-spherical Pt nanoparticles with small crystal sizes were obtained using SWV and 2nd H AC V due to the enhancement of the Pt seed growth by the low-time pulse potential period. Silver incorpora- tion allowed the formation of well-defined cubic-shaped and flower-like PtAg nanoparticles without the need for surfactants and/or reductants. Silver acted both as a silver ion source and an additive, due to its passivation of the particle surfaces. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction The electrodeposition process or electrocrystallisation employs the general theoretical concepts of nucleation, crystal growth and coalescence to form new phases [1]. The nucleation process plays a critical role in metal deposition. The competition between growth and nucleation determines the morphology of a film, such as its granularity [2]. If the nucleation rate during deposition is higher than the growth rate, the resulting crystal grains will be finer. How- ever, if the growth rate exceeds the nucleation rate, the crystal morphology tends to be fibrous or dendritic. Electrochemical techniques can be classified as either stair- case or pulse potential techniques. Typical examples of staircase potential techniques are cyclic voltammetry, linear sweep voltam- metry, chronoamperometry and chronopotentiometry [3]. Pulse ∗ Corresponding author. Tel.: +52 442 211 6069; fax: +52 442 211 6007. E-mail addresses: minbalca@yahoo.com.mx (M. Guerra-Balcázar), larriaga@cideteq.mx (L.G. Arriaga). 1 ISE member. 2 Tel.: +52 4421921200x65421; fax: +52 4421921200x6007. potential techniques include square wave voltammetry, differen- tial pulse voltammetry, differential pulse amperometry, and second harmonic AC voltammetry. Modern voltammetric techniques have been used in a variety of research areas, including biology, chem- istry and pharmaceuticals [4,5]. These techniques aim to investigate the different mechanistic pathways of electroactive chemical or biological compounds [3]. Cyclic voltammetry has been used not only for the detection of molecules but also for the electrodeposition of organic molecules on modified electrodes. To date, numerous molecules have been electrodeposited for various applications, including porphyrins and phthalocyanines for nitric oxide detection [6] and polyaniline for the subsequent chemical deposition of gold nanoparticles [7]. An important advantage of cyclic voltammetry and other electro- chemical techniques is the reproducibility of the resulting film morphology and thickness, which can be controlled by tailoring experimental variables such as the scan rate, potential range, film formation time and type of supporting electrolyte [8]. Square wave voltammetry is the most advanced and sophis- ticated of the pulse voltammetric techniques used for the electroanalytic characterisation of compounds [5]; it has been used for the study of several mechanisms, including protein-film 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.10.100