Fathy M. Hassan

Pyrrolic-structure enriched nitrogen doped graphene for highly efficient next generation supercapacitors

This study reports the preparation of pyrrolic-structure enriched nitrogen doped graphene by hydrothermal synthesis at varied temperature. The morphology, structure and composition of the prepared nitrogen doped graphene were confirmed with SEM, XRD, XPS and Raman spectroscopy. The material was tested for supercapacitive behavior. It was found that doping graphene with nitrogen increased the electrical double layer supercapacitance to as high as 194 F g−1. Furthermore, density functional theory (DFT) calculations showed the proper level of binding energy found between the pyrrolic-nitrogen structure and the electrolyte ions, which may be used to explain the highest contribution of the pyrrolic-structure to the capacitance.

Engineered Si Electrode Nanoarchitecture: A Scalable Postfabrication Treatment for the Production of Next-Generation Li-Ion Batteries

A novel, economical flash heat treatment of the fabricated silicon based electrodes is introduced to boost the performance and cycle capability of Li-ion batteries. The treatment reveals a high mass fraction of Si, improved interfacial contact, synergistic SiO2/C coating, and a conductive cellular network for improved conductivity, as well as flexibility for stress compensation. The enhanced electrodes achieve a first cycle efficiency of ∼84% and a maximum charge capacity of 3525 mA h g(-1), almost 84% of silicons theoretical maximum. Further, a stable reversible charge capacity of 1150 mA h g(-1) at 1.2 A g(-1) can be achieved over 500 cycles. Thus, the flash heat treatment method introduces a promising avenue for the production of industrially viable, next-generation Li-ion batteries.

Flexible High‐Energy Polymer‐Electrolyte‐Based Rechargeable Zinc–Air Batteries

A thin-film, flexible, and rechargeable zinc-air battery having high energy density is reported particularly for emerging portable and wearable electronic applications. This freeform battery design is the first demonstrated by sandwiching a porous-gelled polymer electrolyte with a freestanding zinc film and a bifunctional catalytic electrode film. The flexibility of both the electrode films and polymer electrolyte membrane gives great freedom in tailoring the battery geometry and performance.

Multigrain Platinum Nanowires Consisting of Oriented Nanoparticles Anchored on Sulfur‐Doped Graphene as a Highly Active and Durable Oxygen Reduction Electrocatalyst

Direct growth of multigrain platinum nanowires on sulfur-doped graphene (PtNW/SG) is reported. The growth mechanism, including Pt nanoparticle nucleation on SG, followed by nanoparticle attachment with orientation along the <111> direction is highlighted. PtNW/SG demonstrates improved Pt mass and specific activity compared with commercial catalysts toward oxygen reduction, in addition to dramatically improved stability through accelerated durability testing.

Co-N Decorated Hierarchically Porous Graphene Aerogel for Efficient Oxygen Reduction Reaction in Acid.

Nitrogen-functionalized graphene materials have been demonstrated as promising electrocatalyst for the oxygen reduction reaction (ORR), owning to their respectable activity and excellent stability in alkaline electrolyte. However, they exhibit unacceptable catalytic activity in acid medium. Here, a hierarchically porous Co-N functionalized graphene aerogel is prepared as an efficient catalyst for the ORR in acid electrolyte. In the preparation process, polyaniline (PANI) is introduced as a pore-forming agent to aid in the self-assembly of graphene species into a porous aerogel networks, and a nitrogen precursor to induce in situ nitrogen doping. Therefore, a Co-N decorated graphene aerogel framework with a large surface area (485 m(2) g(-1)) and an abundance of meso/macropores is effectively formed after heat treatment. Such highly desired structures can not only expose sufficient active sites for the ORR but also guarantee the fast mass transfer in the catalytic process, which provides significant catalytic activity with positive onset and half wave potentials, low hydrogen peroxide yield, high resistance to methanol crossover, and remarkable stability that is comparable to commercial Pt/C in acid medium.

Flexible Rechargeable Zinc‐Air Batteries through Morphological Emulation of Human Hair Array

An electrically rechargeable, nanoarchitectured air electrode that morphologically emulates a human hair array is demonstrated in a zinc-air battery. The hair-like array of mesoporous cobalt oxide nanopetals in nitrogen-doped carbon nanotubes is grown directly on a stainless-steel mesh. This electrode produces both flexibility and improved battery performance, and thus fully manifests the advantages of flexible rechargeable zinc-air batteries in practical applications.

Controlled Growth of Platinum Nanowire Arrays on Sulfur Doped Graphene as High Performance Electrocatalyst

Graphene supported Pt nanostructures have great potential to be used as catalysts in electrochemical energy conversion and storage technologies; however the simultaneous control of Pt morphology and dispersion, along with ideally tailoring the physical properties of the catalyst support properties has proven very challenging. Using sulfur doped graphene (SG) as a support material, the heterogeneous dopant atoms could serve as nucleation sites allowing for the preparation of SG supported Pt nanowire arrays with ultra-thin diameters (2–5 nm) and dense surface coverage. Detailed investigation of the preparation technique reveals that the structure of the resulting composite could be readily controlled by fine tuning the Pt nanowire nucleation and growth reaction kinetics and the Pt-support interactions, whereby a mechanistic platinum nanowire array growth model is proposed. Electrochemical characterization demonstrates that the composite materials have 2–3 times higher catalytic activities toward the oxygen reduction and methanol oxidation reaction compared with commercial Pt/C catalyst.

Shape-controlled octahedral cobalt disulfide nanoparticles supported on nitrogen and sulfur-doped graphene/carbon nanotube composites for oxygen reduction in acidic electrolyte

Replacement of expensive platinum-based catalysts at the cathode of fuel cells by low-cost alternatives represents an important milestone to achieve significant system cost reductions. In this work, single crystal cobalt disulfide (CoS2) octahedral nanoparticles supported on graphene/carbon nanotube composites were prepared as oxygen reduction reaction (ORR) catalysts in acidic electrolyte. During the simplistic, one-pot solvothermal synthesis, the nanostructured carbon supports were also simultaneously doped with nitrogen and sulfur. Time dependent studies elucidated the growth process of the {111} facet encased octahedra that could only be prepared when carbon support materials were incorporated into the reaction mixture. Through computational simulations, the shape directed growth process was found to be driven thermodynamically towards surface energy minimization. Control experiments and spectroscopy characterization were also used to investigate the occurrence and nature of nitrogen and sulfur doping into the graphitic structure of the graphene/carbon nanotube composite support. The impact of carbon support on ORR activity was clear, with the graphene/carbon nanotube composite supported CoS2 octahedra (CoS2-CG) outperforming CoS2 supported on just graphene or carbon nanotubes. Additionally, CoS2-CG provided an on-set potential (0.78 V vs. RHE) and half-wave potential (0.66 V vs. RHE) that was 60 mV and 150 mV higher than the CoS2 particle agglomerates formed when no carbon support was included during catalyst preparation. This improved activity can be attributed to the beneficial properties of the nitrogen and sulfur doped graphene/carbon nanotube composite support, and also may arise due to the more favourable oxygen adsorption on the (111) surface of the octahedral particles predicted by theoretical calculations. By combining the synergistic properties of the graphene/carbon nanotube composite and unique shape controlled single crystal CoS2 nanoparticles, CoS2-CG is presented as an emerging catalyst for the ORR in fuel cells.

Evidence of covalent synergy in silicon–sulfur–graphene yielding highly efficient and long-life lithium-ion batteries

Silicon has the potential to revolutionize the energy storage capacities of lithium-ion batteries to meet the ever increasing power demands of next generation technologies. To avoid the operational stability problems of silicon-based anodes, we propose synergistic physicochemical alteration of electrode structures during their design. This capitalizes on covalent interaction of Si nanoparticles with sulfur-doped graphene and with cyclized polyacrylonitrile to provide a robust nanoarchitecture. This hierarchical structure stabilized the solid electrolyte interphase leading to superior reversible capacity of over 1,000 mAh g−1 for 2,275 cycles at 2 A g−1. Furthermore, the nanoarchitectured design lowered the contact of the electrolyte to the electrode leading to not only high coulombic efficiency of 99.9% but also maintaining high stability even with high electrode loading associated with 3.4 mAh cm−2. The excellent performance combined with the simplistic, scalable and non-hazardous approach render the process as a very promising candidate for Li-ion battery technology.

In Situ Polymer Graphenization Ingrained with Nanoporosity in a Nitrogenous Electrocatalyst Boosting the Performance of Polymer-Electrolyte-Membrane Fuel Cells

Rich, porous graphene frameworks decorated with uniformly dispersed active sites are prepared by using polyaniline as a graphene precursor and introducing phenanthroline as a pore-forming agent. The unprecedented fuel-cell performance of this electrocatalyst is linked to the graphene frameworks with vast distribution of pore sizes, which maximizes the active-sites accessibility, facilitates mass-transport properties, and improves the carbon corrosion resistance.