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Ozden, Sehmus

Publications and source records attributed to Ozden, Sehmus.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Molybdenum Carbide Electrocatalysts for Electrochemical Synthesis of Ammonia from Nitrogen: Activity and Stability

Ammonia production has increased from few thousand tons in 1908 to above 200 million tons per year today, revolutionizing the fertilizer industry thanks to the Haber-Bosch (HB) process. However, the HB process is highly energy intensive consuming about 1.4% of fossil energy generated worldwide and releasing 1.87 tons of CO 2 per ton of ammonia produced. This further reduces ammonia’s scope as a carrier fuel for the hydrogen economy. Hence, finding alternative energy efficient ways to synthesize ammonia is important from more than one perspective. Ammonia synthesis from its constituent nitrogen and hydrogen gases is mainly hampered by the nitrogen reduction reaction (NRR) due to the strong N≡N bond (945 kJ mol −1 ). Electrochemical synthesis (ES) routes in this regard offer a milder approach. However, ES of ammonia under different temperatures, utilizing different electrolytes and catalysts has not yet reliably produced ammonia at viable rates and efficiencies. We report an origami-like Mo 2 C cathode catalyst for NRR that achieved a maximum synthesis rate of 2.16 × 10 −11 mol cm −2 s −1 and a faradaic efficiency of 1.8% at 30 °C using Nafion-212 as electrolyte. Origami-like morphology containing numerous kinks appears to improve electrocatalytic activity and show a promising route for fabricating NRR catalysts with higher catalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Origami inspired Three-Dimensional Interconnected Molybdenum Carbide Nanoflakes

High-temperature stable transition metal carbides are one of the promising classes of materials for next-generation energy applications such as water splitting catalysis and electrodes for energy storage devices. Herein, origami-like molybdenum carbide flakes with interfacially connected structures in various orientations using an easily scalable chemical vapor deposition method are synthesized. Interestingly, each individual flake of similar orientation is interconnected across different planes. The interconnected architectures are found to be highly elastic and behave in a sponge-like manner. In addition, the surface energy of each plane is calculated using the first-principle density functional theory. The molybdenum carbide shows excellent activity for the hydrogen evolution reaction, with the onset over potential occurring around -16 to -25 mV with high stability. The material is used as an electrode for supercapacitors as a second demonstration. The supercapacitor constructed with polypyrrole reaches the specific capacitance of ≈279 F g -1 at a current density of 0.5 A g -1 .

36 MATERIALS SCIENCE↗
DOE OSTI2017

Graphene Oxide Epoxy (GO-xy): GO as Epoxy Adhesive by Interfacial Reaction of Functionalities

The unique combination of layered structure and chemical moieties grants very interesting physiochemical properties to graphene oxide (GO). Functional groups such as epoxide, hydroxyl, and carboxyl are abundantly distributed along the hexagonal lattice of carbon atoms. The superior properties of GO and increased interfacial interaction with other compounds make them excellent filler materials in polymers such as epoxies for creating multifunctional composites. Alternatively, the presence of epoxide group on GO opens up the possibility of using it as the major epoxy matrix constituent rather than just as a filler material. In this work, the formation of GO-xy (cross-linked GO via the epoxide functionality) resin is reported by reaction of GO with polymercaptan-based hardener by completely eliminating the need for conventional epoxy component. Substituting epoxy with GO marks notable advance in preparing adhesive materials with high temperature stability.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Bacteria as Bio-Template for 3D Carbon Nanotube Architectures

It is one of the most important needs to develop renewable, scalable and multifunctional methods for the fabrication of 3D carbon architectures. Even though a lot of methods have been developed to create porous and mechanically stable 3D scaffolds, the fabrication and control over the synthesis of such architectures still remain a challenge. Here, we used Magnetospirillum magneticum (AMB-1) bacteria as a bio-template to fabricate light-weight 3D solid structure of carbon nanotubes (CNTs) with interconnected porosity. The resulting porous scaffold showed good mechanical stability and large surface area because of the excellent pore interconnection and high porosity. Steered molecular dynamics simulations were used to quantify the interactions between nanotubes and AMB-1 via the cell surface protein MSP-1 and flagellin. Furthermore, the 3D CNTs-AMB1 nanocomposite scaffold is further demonstrated as a potential substrate for electrodes in supercapacitor applications.

42 ENGINEERING↗
DOE OSTI2017

Lightweight Hexagonal Boron Nitride Foam for CO 2 Absorption

Weak van der Waals forces between inert hexagonal boron nitride (h-BN) nanosheets make it easy for them to slide over each other, resulting in an unstable structure in macroscopic dimensions. Creating interconnections between these inert nanosheets can remarkably enhance their mechanical properties. However, controlled design of such interconnections remains a fundamental problem for many applications of h-BN foams. In this work, a scalable in situ freeze-drying synthesis of low-density, lightweight 3D macroscopic structures made of h-BN nanosheets chemically connected by poly(vinyl alcohol) (PVA) molecules via chemical cross-link is demonstrated. Unlike pristine h-BN foam which disintegrates upon handling after freeze-drying, h-BN/PVA foams exhibit stable mechanical integrity in addition to high porosity and large surface area. Fully atomistic simulations are used to understand the interactions between h-BN nanosheets and PVA molecules. In addition, the h-BN/PVA foam is investigated as a possible CO 2 absorption and as laser irradiation protection material.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Chemically interconnected light-weight 3D-carbon nanotube solid network

Owing to the weak physical interactions such as van der Waals and π-π interactions, which hold nanotubes together in carbon nanotube (CNT) bulk structures, the tubes can easily slide on each other. In creating covalent interconnection between individual carbon nanotube (CNT) structures we saw remarkable improvements in the properties of their three-dimensional (3D) bulk structures. The creation of such nanoengineered 3D solid structures with improved properties and low-density remains one of the fundamental challenges in real-world applications. We also report the scalable synthesis of low-density 3D macroscopic structure made of covalently interconnected nanotubes using free-radical polymerization method after functionalized CNTs with allylamine monomers. The resulted interconnected highly porous solid structure exhibits higher mechanical properties, larger surface area and greater porosity than non-crosslinked nanotube structures. To gain further insights into the deformation mechanisms of nanotubes, fully atomistic reactive molecular dynamics simulations are used. Here we demonstrate one such utility in CO 2 uptake, whose interconnected solid structure performed better than non-interconnected structures.

36 MATERIALS SCIENCE↗