Hanan Teller

Morphological study of branched Sn structure formed under selected electrochemical conditions

A controlled electrodeposition process of branched micrometric and nanometric metallic tin structures was developed. Selected potentiostatic and galvanostatic techniques were explored with the aim of forming hierarchical shaped Sn on carbon porous electrodes by a simple template-free synthesis. We have studied the influence of continuous potential steps ranging from −0.9 to −4xa0V versus Ag/AgCl which show a classical nucleation growth mechanism. Under high overpotentials above −1.5xa0V, the reaction is governed by mass transport, which enables the development of vertically aligned dendrites. Upon reaching a dendrite particle size of 2–5xa0µm, Sn2+ reduction is facilitated on branches extending at an angle of about 45° from the main stem due to enhanced spherical diffusion to these newly evolving sites. A competing reaction of hydrogen evolution plays a significant role during initial nucleation stages and throughout particle evolution by reducing the overall columbic efficiency. Further study of means to affect the mass transport and morphology has led us to investigate the influence of pulse deposition duty cycle as well as use of anionic (SDS—sodium dodecyl sulfate) and cationic (HDTAB—hexadecyltrimethylammonium bromide) surfactants. While short pulses and long rest time promote the formation of high surface density of small nuclei, surfactants directly influence the tin ions (SDS) or adsorbed on the negatively charged electrode (HDTBA). Finally, the study of an electrodeposition method using strong acid additives was developed. It is shown from SEM and EQCM studies that careful selection of the acid type and concentration gives rise to the formation of a much more advanced network structure promoted by selective etching and co-reduction of dissolved ions. Highly interesting two-dimensional tin films formed in this process are also reported.

The Synthesis of Metallic β-Sn Nanostructures for Use as a Novel Pt Catalyst Support and Evaluation of Their Activity Toward Methanol Electrooxidation

This study offers a unique insight into the use of high surface area metallic tin as support material for platinum catalysts for fuel cell application. We have synthesized high surface area metallic β-tin nanostructures (TNSs) in aqueous solutions by novel one-pot process and usedxa0it as a platinum catalyst support in methanol electrooxidation reaction. Rigorous study of parameters controlling the size and shape of TNSs was performed, including selected surfactant molecules at various concentrations, tin salts, and the addition of sodium citrate. Rod-shaped particles with a 50-nm diameter and 500-nm length were obtained from solutions of selected surfactant in concentrations of 1–20xa0mM by sodium borohydride reduction. These particles had a β-Sn crystalline core with a main lattice plane of (101) and were covered by a 4-nm oxide shell. A maximal surface area of 170xa0m2xa0g−1 was measured from a sample prepared by using low concentration of sodium dodecyl sulfate (SDS) (1xa0mM). This samplexa0is composed of nanorods and nano semi-spherical shape tin particles. Addition of sodium citrate, which acts as a Sn2+ ion ligand, yields longer rods. Electrochemical oxidation of methanol on platinum catalyst, supported on metallic Sn nanostructure, exhibits a high activity, which is comparable to commercial carbon-supported platinum catalysts. In situ surface-enhanced Raman (SER), emphasizing the role of surface oxides on the methanol oxidation activity, further studied methanol oxidation on Pt/TNS, Pt/C, and Pt-Sn alloy catalyst.

On the synthesis of RuSe oxygen reduction nano-catalysts for direct methanol fuel cells

Oxygen reduction reaction has a crucial role in energy conversion systems such as fuel cells. State-of-the-art Pt-based cathode catalysts suffer from low efficiency which is severely affected by poisoning of methanol fuel crossing the membrane that separates the electrodes and high cost. We have synthesized a non-platinum RuSe 3–15-nm in size catalysts using microwave irradiation technique, which produces nanomaterials at high efficiency and short time spans. Several Ru/Se atomic ratios of RuSe were prepared using both elemental Se powder and H2SeO3 as precursors. The structure and composition of the obtained materials were characterized using XRD, EDX, ICP-OES, and DSC/TGA. Electrochemical study of oxygen reduction reaction (ORR) on these catalysts was conducted using rotating disk electrode (RDE) technique, from which the Tafel slopes and exchanged current densities of ORR were calculated. The use of H2SeO3 as the Se source provides catalysts with controlled composition. All obtained materials show good electrocatalytic activity towards oxygen reduction and maintain high activity in the presence of high methanol contamination. A rigorous kinetic study of ORR on RuSe catalysts show that at Ru to Se ratio is 2 to 1, and the highest kinetic currents are attained. Stability tests at 0.4xa0V in strong acidic conditions and elevated temperatures, for over 600 hours, exhibit no degradation.

Titanium hydride—a stable support for Pt catalysts in oxygen reduction reaction

A new class of conductive and dimensionally stable surface-modified TiH2 particles prepared by ultra-sonication method is proposed as a non-carbon support for Pt catalysts. Thermal analysis results indicated good thermal stability of these materials at high temperatures in oxygen atmosphere. TiH2 particles are discovered to be stable at potentials higher than 1.5xa0V in O2-saturated H2SO4 solution. It is also found that the surface-modified TiH2 exhibits a modest electrocatalytic activity toward oxygen reduction reaction. Accelerated durability measurements show that Pt catalysts supported on sonicated TiH2 exhibited superior stability than standard Vulcan XC-72 carbon. High corrosion resistance and thermal stability render better chemical stability and structural integrity to surface-modified TiH2 particles at elevated temperatures.

Electrodeposited Ternary Fe-Mo-P as an Efficient Electrode Material for Bifunctional Water Splitting in Neutral pH

AbstractDesigning novel and cost-effective material for electrochemical water splitting in neutral pH are highly essential for the hydrogen production and useful fuel cell construction. Synthesis of the bifunctional and earth-abundant efficient catalyst systems for the same remains one of the biggest challenges to the science community. Herein, we report the electrodeposition of ternary Fe-Mo-P onto the surface of carbon cloth material to form a stable and highly active bifunctional catalyst towards electrochemical hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at pHxa07. A set of catalysts were prepared by varying the relative atomic ratio of the elements and the best catalytic activity was observed with 60 atomic % Fe in the electroplating bath which rivals that of Pt/C in the overall electrochemical water splitting. The best catalyst also shows 24-h stability in the overall electrochemical splitting of water which indicates the potential of this class of materials.n Graphical Abstractᅟ

Exfoliated molybdenum di-sulfide (MoS 2 ) electrode for hydrogen production in microbial electrolysis cell

The most widely reported catalyst in microbial electrochemical cells (MEC) cathodes is platinum (Pt). The disadvantages of Pt include its high cost and sensitivity to various molecules. In this research an exfoliated molybdenum di-sulfide (MoS2-EF) catalyst was synthesized. The size of the obtained particles was 200u202f±u202f50u202fnm, 50-fold smaller than the pristine MoS2 catalyst. The MoS2-EF Raman spectrum displays the E12g and A1g peaks at 373u202fcm-1 and 399u202fcm-1. Electrochemical characterization by linear sweep voltammetry (LSV) of a rotating disc electrode RDE showed that the current density of Pt in 0.5u202fM H2SO4 was 3.3 times higher than MoS2-EF. However, in phosphate buffer (pH-7) electrolyte this ratio diminished to 1.9. The polarization curve of Pt, MoS2-EF and the pristine MoS2 electrodes, at -1.3u202fV in MEC configuration in abiotic conditions exhibit current densities of 17.46, 12.67 and 3.09u202fmAu202fcm-2, respectively. Hydrogen evolution rates in the same MEC with a Geobacter sulfurreducens anode and Pt, MoS2-EF and the pristine MoS2 cathodes were 0.106, 0.133 and 0.083u202fm3u202fd-1u202fm-3, respectively. The results in this study show that MoS2-EF led to highly purified hydrogen and that this catalyst can serve as an electrochemical active and cost-effective alternative to Pt.