Yuhua Xue

Metal-Free Catalysts for Oxygen Reduction Reaction

Liming Dai,*,†,‡ Yuhua Xue,†,‡ Liangti Qu,* Hyun-Jung Choi, and Jong-Beom Baek* †Center of Advanced Science and Engineering for Carbon (Case4Carbon), Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Department of Chemistry, School of Science, Beijing Institute of Technology, Beijing 100081, People’s Republic of China School of Energy and Chemical Engineering/Center for Dimension-Controllable Covalent Organic Frameworks, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon, Ulsan, 689-798, South Korea

Vertically Aligned BCN Nanotubes as Efficient Metal-Free Electrocatalysts for the Oxygen Reduction Reaction: A Synergetic Effect by Co-Doping with Boron and Nitrogen

Abstract : The oxygen reduction reaction (ORR) is an important process in many fields, including energy conversion (fuel cells, metal air batteries), corrosion, and biosensing. For fuel cells, the cathodic oxygen reduction is a major factor limiting their performance. The ORR can proceed either through a four-electron process to directly combine oxygen with electrons and protons into water as the end product, or a less efficient two-step, two-electron pathway involving the formation of hydroperoxide ions as intermediate. Oxygen reduction also occurs, albeit too slowly to be of any practical significance, in the absence of an ORR catalyst on the cathode. Platinum nanoparticles have long been regarded as the best catalyst for the ORR and are still commonly used in fuel cells due to their relatively low overpotential and high current density with respect to other commercial catalysts. However, the ORR kinetics on the Pt-based electrode is sluggish, and the Pt electrocatalyst still suffers from multiple drawbacks, such as susceptibility to fuel crossover from the anode, deactivation by CO, and poor stability under electrochemical conditions. In addition, the high cost of Pt and its limited natural reserves are the major barriers to mass-market fuel cells for commercial applications.

Durable, Self-Healing Superhydrophobic and Superoleophobic Surfaces from Fluorinated-Decyl Polyhedral Oligomeric Silsesquioxane and Hydrolyzed Fluorinated Alkyl Silane†

Super-liquid-repellent surfaces have attracted much attention in both scientific and industrial areas. They are often deemed superhydrophobic or superoleophobic depending on the liquid to be repelled. Superhydrophobic surfaces have a water contact angle greater than 1508. They have interesting nonsticking, self-cleaning, and anti-contamination functions. The emerging applications include separation of oil from water, energy conversion, protection of electronic devices, adjusting cell/substrate adhesion in the biomedical area, and reducing fluid resistance for aquaculture and microfluidic devices. In contrast, superoleophobic surfaces can be rather complicated, but they have great potential applications in antifouling from hazard chemicals and biological contaminants. Although any solid surface can be characterized as superoleophobic as long as its contact angle with an oily fluid is greater than 1508, the surface properties revealed from the contact angle measurement using different contacting oils could be considerably different. For example, a surface that is superoleophobic to certain oily fluids may have lower repellency or even be wettable by other oily fluids of a lower surface tension. It is normally easy to make a surface super-repellent to oils of a high surface tension, but difficult to prepare superoleophobic surfaces against oily fluids that have a surface tension below 35 mNm . Most super-liquid-repellent surfaces have poor durability. Chemical oxidation from exposure to air, a special chemical environment, strong light, or physical rubbing could cause the surfaces to lose their super-repellency permanently. It is imperative to improve the durability for practical applications. Recently, great progress has been made to develop mechanically robust superhydrophobic surfaces and laundering-durable superhydrophobic fabrics. On the other hand, the bioinspired self-healing ability has been proposed to be a promising solution to improve the durability of synthetic superhydrophobic surfaces. Recently, Li et al. reported a self-healing superhydrophobic coating that was prepared by chemical vapor deposition (CVD) of a fluoroalkyl silane on a layer-by-layer assembled porous surface, and self-healing was derived from the reacted fluoroalkyl silane embedded in the rigidly flexible coating layer. Wang et al. also reported the formation of a self-healing superamphiphobic surface on anodized alumina by filling the intrinsic pores with a lowsurface energy liquid. In the recent study, we have also found that fabrics coated with a hydrolysis product from fluorinated-decyl polyhedral oligomeric silsesquioxane (FD–POSS) and a fluorinated alkyl silane (FAS) have a self-healing superhydrophobic and superoleophobic surface and the coating shows excellent durability to acid, UV light, machine wash, and abrasion. Herein, we first report on its novel multiple self-healing ability and durable performance. The chemical structures of FD-POSS and FAS are shown in Figure 1 a. The coating solution was prepared by dissolving FD-POSS in five times its weight of FAS, and the resulting viscous solution was then dispersed in ethanol. After ultrasonication for 30 min, a homogeneous dispersion was obtained. Figure 1b shows the appearance of an FD–POSS/ FAS dispersion in ethanol. Such a suspension was stable at

Highly Efficient Electrocatalysts for Oxygen Reduction Based on 2D Covalent Organic Polymers Complexed with Non‐precious Metals

A class of 2D covalent organic polymers (COPs) incorporating a metal (such as Fe, Co, Mn) with precisely controlled locations of nitrogen heteroatoms and holes were synthesized from various N-containing metal-organic complexes (for example, metal-porphyrin complexes) by a nickel-catalyzed Yamamoto reaction. Subsequent carbonization of the metal-incorporated COPs led to the formation of COP-derived graphene analogues, which acted as efficient electrocatalysts for oxygen reduction in both alkaline and acid media with a good stability and free from any methanol-crossover/CO-poisoning effects.

Transparent and Stretchable High-Performance Supercapacitors Based on Wrinkled Graphene Electrodes

Transparent and/or stretchable energy storage devices have attracted intense attention due to their unique optical and/or mechanical properties as well as their intrinsic energy storage function. However, it remains a great challenge to integrate transparent and stretchable properties into an energy storage device because the currently developed electrodes are either transparent or stretchable, but not both. Herein, we report a simple method to fabricate wrinkled graphene with high stretchability and transparency. The resultant wrinkled graphene sheets were used as both current collector and electrode materials to develop transparent and stretchable supercapacitors, which showed a high transparency (57% at 550 nm) and can be stretched up to 40% strain without obvious performance change over hundreds of stretching cycles.

Vertically Aligned Carbon Nanotube Arrays Co-doped with Phosphorus and Nitrogen as Efficient Metal-Free Electrocatalysts for Oxygen Reduction

Using a mixture of ferrocene, pyridine, and triphenylphosphine as precursors for injection-assisted chemical vapor deposition (CVD), we prepared the first vertically aligned multiwalled carbon nanotube array co-doped with phosphorus (P) and nitrogen (N) with a relatively high P-doping level (designated as PN-ACNT). We have also demonstrated the potential applications of the resultant PN-ACNTs as high-performance electrocatalysts for the oxygen reduction reaction (ORR). PN-ACNT arrays were shown to exhibit a high ORR electrocatalytic activity, superb long-term durability, and good tolerance to methanol and carbon monoxide, significantly outperforming their counterparts doped with P (P-ACNT) or N (N-ACNT) only and even comparable to the commercially available Pt-C catalyst (45 wt % Pt on Vulcan XC-72R; E-TEK) due to a demonstrated synergetic effect arising from the co-doping of CNTs with both P and N.

Hole and Electron Extraction Layers Based on Graphene Oxide Derivatives for High-Performance Bulk Heterojunction Solar Cells

By charge neutralization of carboxylic acid groups in graphene oxide (GO) with Cs(2)CO(3) to afford Cesium-neutralized GO (GO-Cs), GO derivatives with appropriate modification are used as both hole- and electron-extraction layers for bulk heterojunction (BHJ) solar cells. The normal and inverted devices based on GO hole- and GO-Cs electron-extraction layers both outperform the corresponding standard BHJ solar cells.

Functionalization of Graphene Oxide with Polyhedral Oligomeric Silsesquioxane (POSS) for Multifunctional Applications.

Through the amide formation between amine-functionalized polyhedral oligomeric silsesquioxane (POSS) and oxygen-containing groups (e.g., epoxy and carboxyl groups) in graphene oxide (GO), we have synthesized POSS-functionalized graphene nanosheets (POSS-graphene), which are highly soluble in various organic solvents attractive for multifunctional applications. Thin films from solution casting of the resultant POSS-graphene were found to show superhydrophobic properties with a water/air contact angle of ∼157°, while the superhydrophobic POSS-graphene powder could be used to construct liquid marbles. In addition, the POSS-graphene hybrids were also used as novel nanofillers to increase the glass transition temperature (Tg) and decompose temperature (Td) for polymers.

Sulfated Graphene Oxide as a Hole-Extraction Layer in High-Performance Polymer Solar Cells

In this study, we have rationally designed and successfully developed sulfated graphene oxide (GO-OSO3H) with -OSO3H groups attached to the carbon basal plane of reduced GO surrounded with edge-functionalized -COOH groups. The resultant GO-OSO3H is demonstrated to be an excellent hole extraction layer (HEL) for polymer solar cells (PSCs) because of its proper work function for Ohmic contact with the donor polymer, its reduced basal plane for improving conductivity, and its -OSO3H/-COOH groups for enhancing solubility for solution processing. Compared with that of GO, the much improved conductivity of GO-OSO3H (1.3 S m(-1) vs 0.004 S m(-1)) leads to greatly improved fill factor (0.71 vs 0.58) and power conversion efficiency (4.37% vs 3.34%) of the resulting PSC devices. Moreover, the device performance of GO-OSO3H is among the best reported for intensively studied poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) devices. Our results imply that judiciously functionalized graphene materials can be used to replace existing HEL materials for specific device applications with outstanding performance.

Graphene Oxide Nanoribbon as Hole Extraction Layer to Enhance Efficiency and Stability of Polymer Solar Cells

Graphene oxide nanoribbons for efficient and stable polymer solar cells are discussed. With controllable bandgap, good solubility and film forming property, graphene oxide nanoribbons serve as a new class of excellent hole extraction materials for efficient and stable polymer solar cells outperforming their counterparts based on conventional hole extraction materials, including PEDOT:PSS.