Sun-Hee Shin

Edge-selectively antimony-doped graphene nanoplatelets as an outstanding counter electrode with an unusual electrochemical stability for dye-sensitized solar cells employing cobalt electrolytes

A dye-sensitized solar cell (DSSC), one of the present photovoltaic technologies, has always been associated with some problems that make them unsatisfactory for practical use. Among them, developing low-cost, durable, and highly active electrocatalysts such as platinum (Pt) alternatives is one of the urgent issues for practical and/or large-scale commercial applications. In this study, as one of the feasible Pt alternatives, edge-selectively antimony-doped graphene nanoplatelets (SbGnPs) were prepared by a simple eco-friendly mechanochemical reaction between pristine graphite and Sb powder for the use of a counter electrode (CE) in dye-sensitized solar cells, for the first time. The selective doping of metalloid Sb at the edges of graphene nanoplatelets (GnPs) and their structure were confirmed by various analytical techniques including atomic-resolution transmission electron microscopy (AR-TEM). The resultant SbGnPs exhibited a much lower charge-transfer resistance (Rct) compared to that of Pt as electrocatalysts toward a Co(bpy)32+/3+ (bpy = 2,2′-bipyridine) redox couple, displaying ‘zero loss stability’ of electrocatalytic activity for the Co(bpy)33+ reduction reaction even after 1000 potential cycles. DSSCs employing Co(bpy)32+/3+ were systematically evaluated in a comparison with the N-doped graphene nanoplatelet (NGnP) CE as a reference. The SbGnP-CE-based DSSC employing an SGT-021 sensitizer based on a D–π–A structured zinc(II)-porphyrin showed better power conversion efficiency (12.08%) than the Pt (11.26%) or the NGnPs (11.53%). The outstanding electrocatalytic activity of the SbGnPs with an unusual electrochemical stability suggests that they could be a possible candidate as the best alternative to a Pt-CE for DSSCs in conjunction with cobalt electrolytes.

Metalated graphene nanoplatelets and their uses as anode materials for lithium-ion batteries

A series of post-transition metals and semimetals in groups IIIA (Al, Ga, In), IVA (Ge, Sn, Pb) and VA (As, Sb, Bi) were introduced onto graphene nanoplatelets (GnPs) by mechanochemical reaction. The selected metals have a lower electronegativity (χ, 1.61 ≤ χ M ≤ 2.18) but a much larger covalent atomic radius (d M = 120–175 pm) than carbon (χ C = 2.55, d C = 77 pm). The effect of the electronegativity and atomic radius of the metalated GnPs (MGnPs, M = Al, Ga, In, Ge, Sn, Pb, As, Sb, or Bi) on the anode performance of lithium-ion batteries was evalusted. Among the series of prepared MGnPs, GaGnP (χ Ga = 1.81, d Ga = 135 pm) in group IIIA, SnGnP (χ Sn = 1.96, d Sn = 140 pm) in group IVA and SbGnP (χ Sb = 2.05, d Sb = 141 pm) in group VA exhibited significantly enhanced performance, including higher capacity, rate capability and initial Coulombic efficiency. Both the experimental results and theoretical calculations indicated that the optimum atomic size (d M ~ 140 pm) was more significant to the anode performance than electronegativity, allowing not only efficient electrolyte penetration but also fast electron and ion transport across the graphitic layers.

Forming a three-dimensional porous organic network via solid-state explosion of organic single crystals

Solid-state reaction of organic molecules holds a considerable advantage over liquid-phase processes in the manufacturing industry. However, the research progress in exploring this benefit is largely staggering, which leaves few liquid-phase systems to work with. Here, we show a synthetic protocol for the formation of a three-dimensional porous organic network via solid-state explosion of organic single crystals. The explosive reaction is realized by the Bergman reaction (cycloaromatization) of three enediyne groups on 2,3,6,7,14,15-hexaethynyl-9,10-dihydro-9,10-[1,2]benzenoanthracene. The origin of the explosion is systematically studied using single-crystal X-ray diffraction and differential scanning calorimetry, along with high-speed camera and density functional theory calculations. The results suggest that the solid-state explosion is triggered by an abrupt change in lattice energy induced by release of primer molecules in the 2,3,6,7,14,15-hexaethynyl-9,10-dihydro-9,10-[1,2]benzenoanthracene crystal lattice.Porous organic networks are of great fundamental and technological interest. Here, the authors synthesize a three-dimensional porous organic network with high specific surface area via a solid-state explosive reaction of hexaethynyl triptycene single crystals containing primer molecules.

CHAPTER 2:Preparation and Characteristics of Edge-functionalized Graphene Nanoplatelets and Their Applications

For over a decade, graphene has received a lot of attention as a next-generation material, opening new opportunities for multipurpose applications, from wet-chemistry to future electronic devices. Although a variety of established methods for the preparation of graphene and/or graphene-like materials exist, each method has its strengths and weaknesses for commercialization. New prospective methods must be simple, inexpensive, and eco-friendly processes, allowing for mass production with high quality. This can be realized by edge-selective functionalization of graphene nanoplatelets (GnPs) using Friedel–Crafts acylation and mechanochemical reactions. Unlike graphene oxide/reduced graphene oxide, the preparation of edge-selectively functionalized GnPs (EFGnPs) does not include hazardous chemicals. In addition, a variety of functional groups and/or heteroatoms can be selectively introduced at the edges, allowing the tunability of the GnP properties for specific application purposes. Furthermore, the minimal defects in the basal area together with the multifunctionalities of EFGnPs enable the achievement of outstanding performances in various applications, such as in polymer composites, flame retardants, and energy conversion and storage systems. Since this newly-developed method of edge functionalization allows the control of the GnPs characteristics, the resultant EFGnPs have unlimited potential in various applications and they will, indeed, be recognized as next-generation materials soon.