Nanocrystalline nickel-cobalt electrocatalysts to generate ... Electroplating of nanocrystalline

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    i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 1 4 1 1e1 1 4 2 0

    Available online at w

    ScienceDirect

    journal homepage: www.elsevier .com/locate/he

    Nanocrystalline nickelecobalt electrocatalysts to generate hydrogen using alkaline solutions as storage fuel for the renewable energy

    Mosaad Negem a,*, H. Nady a,b, M.M. El-Rabiei a

    a Chemistry Department, Faculty of Science, Fayoum University, Fayoum, Egypt b Chemistry Department, College of Science & Arts in Qurayat, Jouf University, Saudi Arabia

    a r t i c l e i n f o

    Article history:

    Received 6 December 2018

    Received in revised form

    14 March 2019

    Accepted 16 March 2019

    Available online 10 April 2019

    Keywords:

    NieCo alloys

    Electroplating

    Ultrasound

    EIS

    Hydrogen evolution

    * Corresponding author. E-mail address: mra00@fayoum.edu.eg (M

    https://doi.org/10.1016/j.ijhydene.2019.03.128 0360-3199/© 2019 Hydrogen Energy Publicati

    a b s t r a c t

    Generation of hydrogen using an electrocatalyst is valuable research field for the energy

    conversion and storage of the renewable energies. Electroplating of nanocrystalline

    metals and their alloys thin film is auspicious for the conversion and storage of the en-

    ergy in the form of hydrogen fuel during water electrolysis. In this work, we electroplated

    the nanocrystalline NieCo alloys of different Co% using natural compounds such as

    gluconate and cysteine via the galvanostatic-ultrasonication conditions. The electro-

    plated NieCo alloys have been characterized using energy dispersive X-ray, X-ray

    diffraction and scanning electron microscopy, to determine their elemental composition,

    crystal lattice system and surface morphology, respectively. The morphological structure

    of the electroplated NieCo alloys varies from dense and lustrous to granular. The elec-

    troplated NieCo alloys arranged in the face centred cubic or hexagonal closed packaged

    depending on the Co%. The electroplated NieCo alloys arranged in the small unit cell

    which enhances electron transfer and boosts the rate of hydrogen reduction. The elec-

    trocatalytic activity of the electroplated NieCo cathodes towards hydrogen reduction

    reaction was investigated using cathodic polarization and electrochemical impedance

    spectroscopy, EIS, dipped in 1.0 M KOH solution. The electroplated Nie50Co cathode

    displays the superior electrocatalytic activity and the lowest overpotential for the

    hydrogen evolution reaction than bulk Ni.

    © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

    Introduction

    The promising and sustainable fuel is the hydrogen obtained

    from renewable sources such as photovoltaics. The photo-

    voltaic devices are the valuable generator of the electricity but

    the produced electricity is too prohibitive for storage. There-

    fore, it necessitates converting the generated electricity using

    . Negem).

    ons LLC. Published by Els

    the storable form such as hydrogen which can be considered

    the auspicious, clean and ideal fuel for daily life applications.

    Hydrogen is the most abundant element with high energy

    content which can substitute the fossil fuel and hydrogen is

    utilized in the fuel cell to generate efficiently the electricity

    [1e7]. Water electrolysis using alkaline media supplies the

    non-polluting and workable method for the generation of the

    hydrogen fuel. A low-cost production of hydrogen is a key

    evier Ltd. All rights reserved.

    mailto:mra00@fayoum.edu.eg http://crossmark.crossref.org/dialog/?doi=10.1016/j.ijhydene.2019.03.128&domain=pdf www.sciencedirect.com/science/journal/03603199 www.elsevier.com/locate/he https://doi.org/10.1016/j.ijhydene.2019.03.128 https://doi.org/10.1016/j.ijhydene.2019.03.128 https://doi.org/10.1016/j.ijhydene.2019.03.128

  • i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 1 4 1 1e1 1 4 2 011412

    factor for bringing this technology to commercialization [8,9].

    In order to satisfy economic, environmental and technical

    criteria and achieve cheap hydrogen production, it is essential

    to investigate applicable media and cathodes for the genera-

    tion of the hydrogen using water electrolysis. The electrode

    materials used for the HER should attain large and active

    surface area, physically, chemically and electrochemically

    stable, selective, low cost, and safe to use and handle. The

    most important factors influenced electrolysis of water are

    the high charge transfer and the small overpotential. Noble

    metals, such as platinum and ruthenium, are the most suit-

    able and useable materials for this purpose, but they are

    expensive for industrial applications. The electrocatalytic ef-

    ficiency of the HER can be boosted by the synergetic effect of

    the electrocatalytic constituents of the cathode and the

    considerable area of the surface with nanosize grains [10,11].

    Ni and Ni alloys are the most active electrocatalyst in

    concentrated alkaline solutions. The electroplated Ni alloys

    possess the notable electrocatalytic characteristics for the

    reaction of hydrogen reduction and the different catalytic

    processes. The electroplated Ni alloys show the high chemical

    stability in the concentrated alkaline medium, attain the

    appropriatemechanical properties and have inexpensive cost.

    The electrocatalytic activity of Ni towards the hydrogen evo-

    lution was increased by different alloying transition elements

    either binary or ternary Ni alloys such as NieMo, NieCu,

    NieCo, NieZn, NieTi, NiePt, NieV, NieW, and NieFeeZn

    using electroplating techniques [12e22]. The Ni and NieCo

    alloys cathodes characterize by the high electrocatalytic effi-

    ciency with the remarkable amount of the generated

    hydrogen which decrease the energy consumption due to

    improving the reduction mechanism [23e35]. It is supposed

    that the Ni-sites in such NieCo alloy are very well distributed

    over the surface, forming adsorbed, NieH in potential less

    cathodic than other alloys, which leads to hydrogen evolution

    after the first electron transfer [25] by decreasing the energy of

    activation for the HER. The electroplating is the promising

    synthesis technique which enhance formation of homoge-

    neous nanograin structures of small unit cell possessed huge

    surface area leading to the change of the physical and

    chemical characteristics of the electroplatedmetal and alloys.

    The electroplating of NieCo alloys attains the numerous

    benefits such as low cost (compared to Pt or Ru), quick and

    straightforward method to form small unit cell with large

    surface area improving their electrocatalytic properties for the

    hydrogen evolution reaction. Moreover, the electroplated

    NieCo alloys can arranged in the new crystal lattice system

    which can produce novel state of the electronic properties

    enhancing the synergetic effect of electroplated NieCo alloys

    towards the HER. Furthermore, the highly electrocatalytic

    characteristics of NieCo alloys as cathodes towards HER in the

    alkaline solutions encourages to be used for the potential

    application to produce hydrogen gas in the industry [22]. In

    our present work, the nanostructured nickel-cobalt alloys

    have been electroplated from cysteine/gluconate/boric acid

    electrolyte under ultrasonication. The electrocatalytic char-

    acteristics of the nickel-cobalt cathodes were investigated

    towards hydrogen evolution reaction in 1.0 M KOH solutions

    by electrochemical impedance spectroscopy and cathodic

    polarization.

    Experimental

    Alloy nanostructure and characterization

    The electroplating of NieCo alloys was performed on Copper

    foil with 99.98% purity as cathode and the anode was a plat-

    inummesh of 2.4 cm2 surface area. The electroplating ofNieCo

    cathodes was accomplished in a Pyrex cylinder cell using TTI

    PL310 32V-1A PSU as the producer of the galvanostatic current

    and Branson 3510 with the power of 100 W and frequency of

    42 kHz was utilized as the generator of ultrasonic waves. The

    Mettler Toledowas employed to gauge the conductivity and pH

    of the electroplating bath. In addition, the chemicals were

    utilized in the electroplating baths such as cysteine, CoSO4- $7H2O, sodium gluconate, H3BO3 and NiSO4$7H2O obtained

    from Merck and Aldrich-Sigma. The sundry concentrations of

    gluconate (complexing agent), boric acid, cysteine (brightener)

    at different current densities, were applied to improve the

    electroplating of NieCo nanocrystalline alloys. The electro-

    plated NieCo nanocrystalline alloys were obtained from the

    gluconate bath using current density of 5 A dm�2 for 1 h at 293 K and pH 4. The optimized amount of chemicals used

    during electroplating of NieCo alloys is presented in Table 1.

    The electroplating bath was newly prepared for each electro-

    plating experiment. The copper foil cathode was immersed in

    concentrated HNO3 (1:1) to eliminate the Cu oxide layer, af-

    terwards rinsed by deionized water