Kuanping Gong

Bio: Kuanping Gong is an academic researcher from University of Dayton. The author has contributed to research in topics: Nanotube & Carbon nanotube. The author has an hindex of 4, co-authored 4 publications receiving 5908 citations. Previous affiliations of Kuanping Gong include Samsung.

Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction.

Abstract: The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of –80 millivolts and a current density of 4.1 milliamps per square centimeter at –0.22 volts, compared with –85 millivolts and 1.1 milliamps per square centimeter at –0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.

Electrochemistry at Carbon Nanotube Electrodes: Is the Nanotube Tip More Active Than the Sidewall?

Abstract: The molecular engineering of an electrode surface is of paramount importance for the development of electrochemical devices with region-specific electron-transfer capabilities. As they have a unique one-dimensional molecular geometry and excellent electronic properties, carbon nanotubes (CNTs) have been widely used as functional electrodes in various electrochemical systems. Indeed, carbon nanotubes have been demonstrated to enhance the electrochemical activity of biomolecules and to promote the electron-transfer reactions of redox proteins, such as myoglobin, cyctochrome c, and microperoxidase MP-11. Recent studies have suggested that much of the enhanced electrochemical activity and electron-transfer rate at carbon nanotube electrodes arises from the edge-plane-like nanotube ends and that the nanotube sidewall is comparable to the basal plane of highly orientated pyrolytic graphite (HOPG). However, no convincing experimental evidence has been obtained owing to technical difficulties in distinguishing the electrochemical role of the nanotube tip from its sidewall, or vice versa, for conventional randomly orientated nanotubes or relatively short aligned nanotubes. This situation was further complicated by oxygen-containing groups, often introduced through chemical/electrochemical oxidation of the CNT tips or sidewalls, which could affect the nanotube electrode kinetics. The recent availability of superlong ( 5 mm) vertically aligned carbon nanotubes (SLVACNTs) enabled us to study the electrochemistry of the nanotube tip and sidewall specifically by selectively masking regions of the nanotube with a nonconducting polymer coating (e.g. polystyrene, PS) such that the electrolyte has access the nanotube sidewall or tip only. The effectiveness of the polymer masking was checked by fully coating the nanotube with polystyrene under the same conditions: no electrochemical signal was observed at all. Various electrochemical probes, including K3[Fe(CN)6], b-nicotinamide adenine dinucleotide disodium salt hydrate (NADH, reduced form), hydrogen peroxide (H2O2), oxygen, cysteine, and ascorbic acid (AA) with specific electrochemical sensitivities to various surface states of an electrode, were then used to monitor the electrochemical activities of the nanotube tip and sidewall. Depending on the electrochemical species used, we found that both the nanotube tip and sidewall could play a dominant role in electrochemistry at the carbon nanotube electrode. Furthermore, oxygen-containing surface functionalities induced, for example by electrochemical oxidation, were also demonstrated to regulate electrochemical activities of the carbon nanotube electrode. These new findings reported herein address the longstanding issue concerning the relative roles of the nanotube tip and sidewall to electrochemistry at carbon nanotube electrodes, and should facilitate the design and development of novel CNT-based electrodes of practical significance. In a typical experiment, SLVA-CNTs (5 mm long) were produced on a SiO2/Si wafer by the water-assisted chemical vapor deposition (CVD) of high-purity (99.99%) ethylene in the presence of an Fe catalyst with helium/H2 (2.5:1 v/v) as a carrier gas under 1 atm pressure at 700 8C. Figure 1a shows a digital photograph of the as-synthesized SLVA-CNT array. The corresponding scanning electron microscope (SEM) image is reproduced in Figure 1b, which shows closely packed well-aligned individual nanotubes. Transmission electron microscopic (TEM) observation of the constituent nanotubes individually dispersed in ethanol clearly reveals a double-walled carbon nanotube (DWNT) with an average outer diameter of 4 nm (Figure 1c). Figure 1d shows a schematic representation of the procedure for preparing the nanotube electrode from the assynthesized SLVA-DWNTarray. To start with, a small bundle of the superlong CNTs was taken out from the as-synthesized SLVA-DWNTs and connected to a copper wire (Step 1 in Figure 1d) with silver epoxy (see inset in Figure 1d). The CNT electrode with only the nanotube tip exposed (designated as the CNT-T electrode) was then prepared by thoroughly coating the copper-wire-supported CNTs with a PS solution (15 wt% in toluene) and drying at 50 8C in air (Step 2 in Figure 1d), followed by partially cutting off the free end of the polymer-wrapped CNTs (Step 3 in Figure 1d). The access of aqueous electrolytes to the innerwall of the wt nanotube can be effectively limited by the hydrophobic nature of the small DWNT. On the other hand, the CNT electrode with only the nanotube sidewall exposed (designated as the CNT-S electrode) was prepared by coating the two ends of the copper-wire-supported CNTs with the PS solution and drying at 50 8C in air (Step 4 in Figure 1d). To prepare the corresponding nanotube electrodes with oxygencontaining surface functionalities (designated as O-CNT-T and O-CNT-S), the newly prepared CNT-T and CNT-S electrodes were polarized at 1.8 V in 0.1m phosphate-buffered [*] Dr. K. Gong, Dr. S. Chakrabarti, Prof. Dr. L. Dai Department of Chemical and Materials Engineering and Department of Chemistry and UDRI University of Dayton 300 College Park, Dayton, OH 45469 (USA) Fax: (+1)937-229-3433 E-mail: ldai@udayton.edu

Structural Evaluation along the Nanotube Length for Super-long Vertically Aligned Double-Walled Carbon Nanotube Arrays

Abstract: By performing Raman spectroscopic and electrochemical measurements along the nanotube length, we have demonstrated that there is a concentration gradient of structural defects along the tube length for super-long (ca. 5 mm) vertically aligned double-walled carbon nanotubes (SLVA-DWNTs) produced by water-assisted CVD growth. An increase in the structural defect content along the nanotube length from the top to bottom end was observed in the present study due to the “bottom growth” process and the decay of the catalyst reactivity with the growth time. The newly observed defect content gradient facilitated us to tune the nanotube electrochemistry along its length and to deposit metal particles in a length-specific fashion.

Metal-Free Electrocatalysts for Oxygen Reduction

Abstract: Polymer electrolyte membrane (PEM) fuel cells are attracting much attention as promising clean alternative power sources to conventional power sources, including internal combustion engines and secondary batteries. Electrocatalysts for the oxygen reduction reaction (ORR) are a key component of PEM fuel cells, which convert chemical energy directly into electricity by coupling the ORR with the oxidation of fuel molecules at the other electrode via the diffusion of ions through the membrane. Although Pt-based ORR catalysts are given high priority in formulating electrodes for PEM fuel cells, they still suffer from multiple competitive disadvantages, including their high cost, susceptibility to CO gas poisoning, and fuel crossover effect. Due to their unique electrical and thermal properties, wide availability, environmental acceptability, corrosion resistance, and large surface area, certain carbon nanomaterials have recently been studied as metal-free ORR electrocatalysts to circumvent those issues associated with the Pt catalyst. Much effort has been devoted to developing metal-free ORR catalysts for fuel cells, which led to great advances in both fundamental and applied research. In this chapter, we present an overview on recent progresses in the development of metal-free ORR electrocatalysts for fuel cells.

Combining theory and experiment in electrocatalysis: Insights into materials design

Abstract: BACKGROUND With a rising global population, increasing energy demands, and impending climate change, major concerns have been raised over the security of our energy future. Developing sustainable, fossil-free pathways to produce fuels and chemicals of global importance could play a major role in reducing carbon dioxide emissions while providing the feedstocks needed to make the products we use on a daily basis. One prospective goal is to develop electrochemical conversion processes that can convert molecules in the atmosphere (e.g., water, carbon dioxide, and nitrogen) into higher-value products (e.g., hydrogen, hydrocarbons, oxygenates, and ammonia) by coupling to renewable energy. Electrocatalysts play a key role in these energy conversion technologies because they increase the rate, efficiency, and selectivity of the chemical transformations involved. Today’s electrocatalysts, however, are inadequate. The grand challenge is to develop advanced electrocatalysts with the enhanced performance needed to enable widespread penetration of clean energy technologies. ADVANCES Over the past decade, substantial progress has been made in understanding several key electrochemical transformations, particularly those that involve water, hydrogen, and oxygen. The combination of theoretical and experimental studies working in concert has proven to be a successful strategy in this respect, yielding a framework to understand catalytic trends that can ultimately provide rational guidance toward the development of improved catalysts. Catalyst design strategies that aim to increase the number of active sites and/or increase the intrinsic activity of each active site have been successfully developed. The field of hydrogen evolution, for example, has seen important breakthroughs over the years in the development of highly active non–precious metal catalysts in acid. Notable advancements have also been made in the design of oxygen reduction and evolution catalysts, although there remains substantial room for improvement. The combination of theory and experiment elucidates the remaining challenges in developing further improved catalysts, often involving scaling relations among reactive intermediates. This understanding serves as an initial platform to design strategies to circumvent technical obstacles, opening up opportunities and approaches to develop higher-performance electrocatalysts for a wide range of reactions. OUTLOOK A systematic framework of combining theory and experiment in electrocatalysis helps to uncover broader governing principles that can be used to understand a wide variety of electrochemical transformations. These principles can be applied to other emerging and promising clean energy reactions, including hydrogen peroxide production, carbon dioxide reduction, and nitrogen reduction, among others. Although current paradigms for catalyst development have been helpful to date, a number of challenges need to be successfully addressed in order to achieve major breakthroughs. One important frontier, for example, is the development of both experimental and computational methods that can rapidly elucidate reaction mechanisms on broad classes of materials and in a wide range of operating conditions (e.g., pH, solvent, electrolyte). Such efforts would build on current frameworks for understanding catalysis to provide the deeper insights needed to fine-tune catalyst properties in an optimal manner. The long-term goal is to continue improving the activity and selectivity of these catalysts in order to realize the prospects of using renewable energy to provide the fuels and chemicals that we need for a sustainable energy future.

Co3O4 nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction

Abstract: Catalysts for oxygen reduction and evolution reactions are at the heart of key renewable-energy technologies including fuel cells and water splitting. Despite tremendous efforts, developing oxygen electrode catalysts with high activity at low cost remains a great challenge. Here, we report a hybrid material consisting of Co₃O₄ nanocrystals grown on reduced graphene oxide as a high-performance bi-functional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Although Co₃O₄ or graphene oxide alone has little catalytic activity, their hybrid exhibits an unexpected, surprisingly high ORR activity that is further enhanced by nitrogen doping of graphene. The Co₃O₄/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions. The same hybrid is also highly active for OER, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER. The unusual catalytic activity arises from synergetic chemical coupling effects between Co₃O₄ and graphene.

Carbon Nanotubes: Present and Future Commercial Applications

Abstract: Worldwide commercial interest in carbon nanotubes (CNTs) is reflected in a production capacity that presently exceeds several thousand tons per year. Currently, bulk CNT powders are incorporated in diverse commercial products ranging from rechargeable batteries, automotive parts, and sporting goods to boat hulls and water filters. Advances in CNT synthesis, purification, and chemical modification are enabling integration of CNTs in thin-film electronics and large-area coatings. Although not yet providing compelling mechanical strength or electrical or thermal conductivities for many applications, CNT yarns and sheets already have promising performance for applications including supercapacitors, actuators, and lightweight electromagnetic shields.

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Abstract: Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...