Selenium, depending on its crystal structure, can exhibit various properties and, as a result, be used in a wide range of applications. However, its exploitation has been limited due to the lack of understanding of its complex growth mechanism. In this work, template-free electrodeposition has been utilized for the first time to synthesize hexagonal-selenium (t-Se) microstructures of various morphologies at 80°C. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) revealed 5 reduction peaks, which were correlated with possible electrochemical or chemical reaction related to the formation of selenium. Potentiostatic electrodeposition using 100 mM SeO 2 showed selenium nanorods formed at−0.389 V then increased in diameter up to −0.490 V, while more negative potentials (-0.594 V) induced formation of sub-micron wires with average diameter of 708 ± 116 nm. Submicron tubes of average diameter 744 ± 130 nm were deposited at −0.696 V. Finally, a mixture of tubes, wires, and particles was observed at more cathodic potential due to a combination of nucleation, growth, dissolution of structures as well as formation of amorphous selenium via comproportionation reaction. Texture coefficient as a function of applied potential described the preferred orientation of the sub-microstructures changed from (100) direction to more randomly oriented as more cathodic potentials were applied. Lower selenium precursor concentration lead to formation of nanowires only with smaller average diameters (124 ± 42 nm using 1 mM, 153 ± 46 nm using 10 mM SeO 2 at −0.389 V). Time-dependent electrodeposition using 100 mM selenium precursor at −0.696 V explained selenium was formed first as amorphous, on top of which nucleation continued to form rods and wires, followed by preferential dissolution of the wire core to form tubes.

As the fossil fuel is continuously declining, the necessity of a sustainable and clean source of energy is increasing. Hydrogen has been considered as a potential alternative due to its “zero emission” when reacting with oxygen in electrochemical cells. In addition, hydrogen is also a promising energy carrier/ storage to compensate the intermittent nature of other renewable energy sources (e.g. sunlight, wind, and tides). However, majority of hydrogen production comes from the combustion of fossil fuel which doesn’t make hydrogen a practical sustainable energy. Electrocatalytic hydrogen evolution reaction (HER) in water electrolysis therefore has drawn considerable attention owing to water and oxygen as the “green” reactant and by-product respectively. Early works with electrocatalytic HER involved noble metals (e.g. Pt) which is not cost-effective for industrial scale production. Therefore, transitional metal-based electrocatalysts (TMEs) have been intensively studied owing to the affinity of unpaired d-band electrons for chemisorption of hydrogen atoms. Among different strategies to improve the intrinsic properties of TMEs, coupling with other materials synergistically promotes the kinetics of HER. Nickel with minimum energy for hydrogen adsorption among various nonprecious metals exhibits the most efficient catalytic activities as a binary alloy with molybdenum in alkaline HER. Hydrogen spillover and averaging effect between the hydrogen adsorption energies of nickel and molybdenum facilitate the catalytic activity of nickel molybdenum alloy. On the other hand, transitional metal phosphides, especially cobalt with similar energy for hydrogen adsorption as nickel, have been considered as promising TMEs for acidic HER. With high electronegativity, phosphorus atoms can trap the positively charged protons and consequently enhance the dissociation of hydrogen. Moreover, dissolution of phosphorus-doped cobalt is less thermodynamically favored than that of cobalt, resulting in better electrocatalytic stability. To further enhance the HER catalytic performance, both types of electrocatalysts are synthesized at non-equilibrium by electrodeposition techniques to introduce chemical disorders and metaphases as well as to widen the range of composition. Different properties of deposits (e.g. composition, morphology, and grain size) can be tuned by controlling electrolyte composition and electrodeposition parameters.

Nanocrystalline cobalt-phosphorus (Co100-xPx) thin films were electrodeposited and their extrinsic magnetic properties were systematically studied by controlling various synthesis parameters. The crystalline thin films exhibited the perpendicular anisotropy which had the behavior of stripe domains. The incorporation of phosphorus (P) atoms into cobalt (Co) lattice structure resulted in the transition from single to pseudo-domain particles. As P content augmented in the crystalline deposits, P precipitation at the grain boundary served as pinning sites, resulting in higher coercivity. Further increase in P content reduced the crystallinity of the deposits and thereby lowered perpendicular anisotropy and coercivity. Promotion of P content was observed at higher NaH2PO2 concentration, lower pH, and smaller film thickness. Temperature was also adjusted to tune P content by controlling the fraction of free Co2+ ions and complexes Co(NH3)x 2+ in solution.

During past years, one-dimensional nanostructures such as nanotubes and nanowires have drown much attention due to the possibility of their application in nanodevices. This is due to their size-dependent physical properties. Selenium is known to be an important elemental semiconductor which has been widely studied because of the exhibition of so many appealing properties such as high photoconductivity and low photomelting temperature, high piezoelectric, thermoelectricity, and non-linear optical responses. There has been extensive research on Selenium nanowires and nanorods among all Se nanostructures. Se nanowires can be fabricated by using solution-phase method, chemical vapor deposition method, and electrodeposition. The electrodeposition technique is more promising due its simplicity, cost-effectiveness, and low growth temperature. In the present work, we are looking forward to fabricating one-dimensional trigonal Selenium nanowires using electrodeposition. The morphology is controlled as a function of applied potential and pH in the electrolytes. The temperature-dependent annealing will also be performed. The morphology and crystallinity of the Se nanostructures are characterized by Raman spectra, TEM, SEM, and XRD. The electrodeposition of trigonal Selenium nanostructures is demonstrated based on an analysis of linear sweep voltammetry and pH-Eh (pourbaix) diagram.