Commensurate Phases of Gases Adsorbed on Carbon Nanotubes

A study is presented of the nature of ordered phases of various gases adsorbed on an isolated carbon nanotube. Because the spacing between neighboring adsorption sites depends on the tube\u27s radius R, the equilibrium structure of the ground state is predicted to differ from that observed on planar graphite. Results for this structure are presented for the inert gases and hydrogen as a function of R for zigzag nanotubes

Environmental Sustainability Education at the University of Michigan: Collaboration with Industry to Provide Experiential Learning Opportunities

The Concentrations in Environmental Sustainability (ConsEnSus) Program at the University of Michigan is a new multi-disciplinary opportunity for graduate students in the College of Engineering to pursue interests in environmental sustainability white obtaining a traditional engineering Master\u27s degree. Students from several engineering departments complement traditional disciplinary course requirements with courses in environmental regulations, policies, and technology. A required case studies course of the ConsEnSus Program brings practicing engineers together with students to discuss real-world sustainability problems. The industrial participants interactively present relevant case studies, and provide opportunities for experiential learning through classroom activities and term projects. This paper will further explain the ConsEnSus Program, its implementation, the initial successes of the program, and the case studies course and term project that was developed in collaboration with industry

Induced Defects in Carbonaceous Materials for Hydrogen Storage

The induced defects in carbonaceous materials for hydrogen storage were studied. The effect of exfoliation was studied and the graphite nanofibers (GNF) diameter before and after exfoliation was quantified. Thermal decomposition of the GNF before and after sulfuric/nitric acid exfoliation indicated a clear loss of thermal stability. GNF exfoliation enhanced the hydrogen uptake by a factor of five compared to the untreated GNF. The amorphous carbon was reactive than GNF, and decomposed before the GNF. The higher pretreatment temperature was intended to preferentially remove amorphous carbon leaving a higher purity of exfoliated GNF

Vibrational Modes of ⁴He and H₂ Gases Adsorbed on Carbon Nanotubes

We present calculations of the breathing mode phonon frequencies of 4He and H2 physically adsorbed on the outside surface of one or more carbon nanotubes. Two geometries are considered. The first is a single, isolated nanotube, upon which the gas is adsorbed as a commensurate phase. The second is a quasi-one-dimensional groove phase nestled between two nanotubes. While the computed breathing mode frequencies depend on nanotube radius and the adsorbate, in general, they are of the same order of magnitude as those of the bare nanotubes

Using Student Ambassadors to Relay Themes from Changing the Conversation in Engineering First Year Seminars

This paper describes the efforts at a large mid-Atlantic university to integrate themes from Changing the Conversation into First Year Seminars. Changing the Conversation, a 2008 book by the National Academy of Engineering, found that both male and female students were more attracted to messages describing engineering in terms relating to societal impact, such as the phrases, Engineering makes a world of difference and Engineering is essential to our health, happiness, and safety. Although the research was conducted with younger students, the potential for using these themes in the undergraduate curricula could have the potential to impact persistence in engineering, especially for female students or those from other underrepresented groups. The purpose of the initiative described in the paper, which uses engineering students from a group called the Engineering Ambassadors to relay these messages in freshmen level courses, is to impact student perceptions of engineering and to provide information to students that will be critical in making career decisions. In the Fall of 2011, a pilot program was launched in two sections of a Chemical Engineering First Year Seminar. Engineering Ambassadors made four separate visits to each section, focusing on the following topics: 1) An overview of College of Engineering Majors, 2) Options within Chemical Engineering, 3) Student experiences in the College of Engineering, and 4) How to be a successful engineering student. Woven through each presentation were themes from Changing the Conversation, focusing on how engineers are essential to health, happiness and safety. The students were mentored by a faculty member whose background is in Communication. The quality of student presentations was high, utilizing the assertion-evidence method of slide design. Data was collected to determine whether the following project objectives were met: 1) Students in the First Year Seminars will have a greater understanding of the possible careers in engineering as well as the engineering majors; and 2) Students will be more likely to define engineering in terms associated with health, happiness, and safety. The data showed that the students had a very positive reaction to the Engineering Ambassador visits, although a larger sample size would be necessary to more clearly understand the impact

Gas Adsorption in Novel Environments, Including Effects of Pore Relaxation

Adsorption experiments have been interpreted frequently with simplified model geometries, such as ideally flat surfaces and slit or cylindrical pores. Recent explorations of unusual environments, such as fullerenes and metal-organic-framework materials, have led to a broadened scope of experimental, theoretical and simulation investigations. This paper reviews a number of such studies undertaken by our group. Among the topics receiving emphasis are these: universality of gas uptake in pores, relaxation of a porous absorbent due to gas uptake and the novel phases of gases on a single nanotube, all of which studies have been motivated by recent experiments

Penn State University NSF GK-12 Project: Using Web-Based Education and Interaction with K-12 and College Freshman to Promote Science and Engineering

Penn State University has hosted an NSF-sponsored GK-12 Outreach project for the past five years, and has just begun the second phase of the project. The Penn State project utilizes the talents of many science and engineering graduate students as teachers, mentors and role models for the K-12 classrooms. The project focuses on developing skills of students in the areas of science, technology, engineering and mathematics through the use of Advanced Transportation Technologies. A new project component was devised and implemented-the interaction of K-12 students with college freshman via a website project. The college freshmen were asked to create a website describing a component of Clean Energy , which was to include an assessment tool to provide feedback on their website. When possible, the college freshmen were encouraged to use active learning and inquiry-based learning concepts. This was encouraged so that the college freshman had an opportunity to practice developing scientific inquiry as a skill through a presentation, and provided the K-12 classroom students a unique opportunity to learn through inquiry. The K-12 students were invited to participate in the research by reviewing and critiquing these websites through feedback via the website to the college freshman. The feedback could take many forms, including specific comments and critique along with a creative assessment tool that the college freshman decided to present with their subject materials. This paper will review the educational outcomes garnered by the students, and provide feedback and analysis from the K-12 and college freshman participants

DEVELOPMENT OF DOPED NANOPOROUS CARBONS FOR HYDROGEN STORAGE

Hydrogen storage materials based on the hydrogen spillover mechanism onto metal-doped nanoporous carbons are studied, in an effort to develop materials that store appreciable hydrogen at ambient temperatures and moderate pressures. We demonstrate that oxidation of the carbon surface can significantly increase the hydrogen uptake of these materials, primarily at low pressure. Trace water present in the system plays a role in the development of active sites, and may further be used as a strategy to increase uptake. Increased surface density of oxygen groups led to a significant enhancement of hydrogen spillover at pressures less than 100 milibar. At 300K, the hydrogen uptake was up to 1.1 wt. % at 100 mbar and increased to 1.4 wt. % at 20 bar. However, only 0.4 wt% of this was desorbable via a pressure reduction at room temperature, and the high lowpressure hydrogen uptake was found only when trace water was present during pretreatment. Although far from DOE hydrogen storage targets, storage at ambient temperature has significant practical advantages oner cryogenic physical adsorbents. The role of trace water in surface modification has significant implications for reproducibility in the field. High-pressure in situ characterization of ideal carbon surfaces in hydrogen suggests re-hybridization is not likely under conditions of practical interest. Advanced characterization is used to probe carbon-hydrogen-metal interactions in a number of systems and new carbon materials have been developed

Hydrogen Spillover Modeling: Applications in Hydrogen Storage

A model of hydrogen spillover that provides a mechanistic understanding of the resulting surface concentration attributed to hydrogen spillover is proposed. Four models are developed to describe this process, including a chemical kinetics model, a kinetic Monte Carlo analysis, a dimensional analysis of the process, and use of a Langmuirian model to provide a simplified chemical kinetics analysis. The fourth model is presented in detail and its resulting spillover isotherm, which has allowed comparison of recent experimental results in hydrogen storage of doped carbon nanomaterials at ≤ 20 bar. Langmuir discussed a fifth case of adsorption, which involved dissociation of the adsorbate and ultimately led to this common assertion. However, Langmuir clearly states that this equation is valid only in the limiting case where surface coverage approaches zero. The spillover isotherm fits experimental data for a 1% Pt/SWNT very well at ≤ 20 bar. The spillover isotherm exhibits properties similar to that of the classic Langmuir isotherm. This limiting capacity provides a more realistic view of potentially applying carbon-metal hybrids to hydrogen-storage applications, than the common statement that uptake is proportional to the square root of pressure. This is an abstract of a paper presented at the ACS Fuel Chemistry Meeting (San Diego, CA Spring 2005)

Stochastic and Dimensional Analysis of High-Pressure Hydrogen Adsorption via Spillover on Carbon Supported Catalyst

Carbon metal synergy in the form of hydrogen spillover can significantly increase the uptake of a carbon-based hydrogen storage material. The fundamental processes involved in hydrogen spillover are: adsorption of active hydrogen species, desorption of hydrogen species as molecular hydrogen, and surface diffusion of hydrogen species. The rates of these processes are suggested to be system dependent and it is not fully clear whether or when the hydrogen spillover process is a function of metal dispersion, metal particle size, metal loading, and metal-carbon interface. The hypothesis that hydrogen surface coverage will be determined by the competing rates of desorption vs. surface diffusion lends itself to a dimensional analysis of the spillover process. The dimensional analysis, combined with a kinetic Monte Carlo model, studied the effect of hydrogen pressure; relative activation energies of the processes involved; active metal and carbon surface area; and length of metal-support interface. These theoretically-grounded models facilitated optimization of hydrogen storage materials beyond a trial and error approach. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcas