7月9日小松讲堂

09 : 00 – 09 : 40高纬Graphene Oxide in Supercapacitors and Fuel Cells

09 : 40 – 10 : 20郭仕锐Anomalous ionic conductivity in sub-5-nm carbon nanotube nanochannels

7月10日小松讲堂

09 : 00 – 09 : 40楼峻Quantitative In-Situ Mechanical Characterization of Low Dimensional Carbon Nanomaterials

09 : 40 – 10 : 20池其金Mixed-valence Nanoparticle Electrocatalyst-----Biomimetic Long-range Electron Transfer and Enzyme-like Electrocatalysis

Graphene Oxide in Supercapacitors and Fuel Cells

Wei Gao, Assistant Professor in TECS @ NCSU

Breakthroughs in energy conversion and storage technologies are desired throughout the world due to the ever-growing demand for energy. Supercapacitors, as important supplement to batteries, offer much higher power density but with limited energy density. Hydrogen-air fuel cells, on the other hand, are environmental-friendly but expensive alternatives to existing power supplies in both transportation and stationary applications. Both technologies are in their embryonic states, but are heavily investigated by researchers all over the world. This talk will introduce Dr. Gao’s research activities in related topics, but with focuses on a new material, graphene oxide^[1], which was once noted as an important precursor to graphene. There now exists an extensive literature regarding the synthesis, chemical structure, reactivity, properties of GO, as well as its use in multiple applications. Our work here use films of GO as proton conductors in both supercapacitors^[2]and hydrogen-air fuel cells^[3]. Degradation of GO has been reported, which presents a significant challenge for all potential applications of GO^[4]. We show that degraded GO can regain epoxy groups with ozone treatment and result in 75% increase of the proton conductivity. Overall, free-standing ozonated GO films offer improved device performance when used in supercapacitors and hydrogen fuel cells as proton conductors.

由于世界范围内的能源危机和环境污染，绿色环保的能源转化和储存技术是当前各国的研究热点。在这个领域内的技术革新是大家迫切需要的。超级电容器，作为电池技术的重要补充，通常用于需要瞬间大功率的工作环境（如起重机），但是在能量密度（即续航力）上与电池还有一定的差距。另一方面，氢燃料电池，由于其转化产物为水，被认为是非常环保及高效的化学能与电能的转化装置。但是，它通常需要铂等贵金属作为催化剂，价格过高而限制了其商业化。这两项技术都处在萌芽阶段，但世界各国都投入了大量研究经费进行开发。在这里，我将介绍本人在相关领域的研究经历，但侧重于一个非常重要的新型材料，氧化石墨烯。氧化石墨烯在过去的十年中，因为被认为是制备石墨烯的重要前躯体而得到广泛重视。目前关于它的合成，结构，性质，和应用的报道已经大量出现。我们的工作主要集中在将氧化石墨烯的膜作为质子导体而用于超级电容器和燃料电池中。在2012年，有研究报道氧化石墨烯在室温下不稳定，从而影响了它在很多领域的应用。我们针对这一报道，采用了臭氧液相处理的方法，将石墨烯的氧化程度提高并改进了它的质子电导率。经过臭氧化的石墨烯膜在超级电容器和燃料电池中成功提高了整个器件的性能。

Anomalous ionic conductivity in sub-5-nm carbon nanotube nanochannels

Abstract:

Fundamental understanding of ionic and molecular transport phenomena in a simple model nanopore is critical for elucidating function mechanisms of much more complex biological systems, and for advancing technological areas such as membrane separation, energy harvesting/storage, and single molecule detection. For this goal, carbon nanotubes (CNTs) offer key advantages as model nanofluidic channels due to their simple chemical composition and structure (known with atomic precision), robustness, facile length and diameter control, and straightforward local functionalization at their open rim. CNTs have also very interesting (and poorly understood) fluidics properties such as enhanced pressure-driven fluid transport rates, unusually high electroosmotic flow, and ionic selectivity.

Here, we demonstrated a novel and robust nanofluidic platform featuring an individual carbon nanotube (CNT) as the flow channel in an advanced Coulter Counter. To fabricate the CNT nanofluidic device, vertically aligned single-walled CNTs are synthesized directly on a suspended silicon nitride membrane and then bound in a solid matrix before an individual CNT is opened by focused ion beam milling. Single-molecule translocation studies with small molecular size analytes suggest the successful fabrication of a Coulter Counter with a-few-nm wide CNT nanochannel. We observed a power-law increase of conductance with KCl concentration (G ~ cn, n<1 ) in cnt channels, a dependence that seems to be unique of cnt pores.

Abstract:

The perfect graphene is believed to be the strongest material. However, the useful strength of large-area graphene with engineering relevance is determined by its fracture toughness, rather than the intrinsic strength that governs the uniform breaking of atomic bonds in perfect graphene. Here, we report the in situ tensile testing of suspended graphene using a nanomechanical device to measure the fracture toughness of graphene. During tensile loading, the cracked graphene samples fracture at a breaking stress substantially lower than the intrinsic strength of graphene. Our combined experiment and modeling verify the applicability of the classic Griffith theory of brittle fracture to graphene. Also in this talk, I will briefly review some of our other efforts in studying mechanical behaviours of various one-dimensional carbon nanomaterials such as carbon nanofibers and carbon nanotubes as well as related interfaces in nanocomposites using the advanced in-situ nanomechanical measurement techniques.

Brief Biography: Jun Lou obtained B.E. and M.S. degrees in Materials Science and Engineering from Tsinghua University and Ohio State University, respectively, and his Ph.D. degree from the Department of Mechanical and Aerospace Engineering and Princeton Materials Institute at Princeton University. After a brief postdoc at Brown University he joined the Department of Mechanical Engineering and Materials Science at Rice University, and currently is a professor and the associate chair of the Department of Materials Science and NanoEngineering. He is a recipient of the US Air Force Office of Scientific Research Young Investigator Award and the ORAU Ralph E. Powe Junior Faculty Enhancement Award. His research interests include nanomaterial synthesis, nanomechanical characterization and nanodevice fabrication for energy, environmental and biomedical applications.

Long-range electron transfer (LRET) is a core elementary step in a wealth of processes central to chemistry and biology including photosynthesis, respiration, and catalysis. In nature, biological catalysis is performed by enzymes. However, enzymes are structurally fragile and stability limited in in-vitro environments. This challenge has promoted the development of robust biomimetic nanostructures with desirable bio-mimicking functions. To date, the synthesis of protein-size and enzyme-like nanostructures with high stability and substrate affinity offers new opportunities but also raises other challenges. In this lecture, by usingPrussianBlueas an example I will address the preparation of highly stable and water-soluble mixed-valence nanoparticles under mild chemical conditions and mapped their enzyme-mimicking catalytic features.Controlled LRET and electrocatalysis with single-nanoparticle resolution could be achieved by a combination of several advanced tools. Experimental observations and theoretical analysis offer clues for understanding the observed correlation of interfacial ET kinetics with catalytic efficiency.

About Speaker：

Dr. QijinChireceivedhis PhD in physical and analytical chemistry from Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. After his postdoc experience as aJSPS fellow in Japan and as a DFG fellow at the Institute of Physical and Theoretical Chemistry, Tübingen University, Germany; he joinedDTU Chemistry, Technical University of Denmark (DTU)as an assistant professor, where he is currently an associate professor of physical chemistry and nanochemistry. He also studied and worked in Johns Hopkins University School of Medicine for over three years. His research interests cover electrochemistry, surface self-assembly chemistry, single-molecule charge transfer and electronics, and chemically designed and synthesized nanoparticles and graphene based materials for their applications in chemical sensors, biosensors and advanced energy technology. He is a member of several professional societies, notably as an elected member of the Danish Academy of Natural Sciences since 2012.