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News Article | February 27, 2017
Site: www.eurekalert.org

Most strategies to combat climate change concentrate on reducing greenhouse gas emissions by substituting non-carbon energy sources for fossil fuels, but a task force commissioned in June 2016 by former U.S. Secretary of Energy Ernest Moniz proposed a framework in December 2016 for evaluating research and development on two additional strategies: recycling carbon dioxide and removing large amounts of carbon dioxide from the atmosphere. These strategies were developed under a single framework with the goal to produce an overall emissions reduction for the Earth of at least one billion tons of carbon dioxide per year. Task force members said that these approaches would complement carbon-free approaches based on electrification, including wind and solar energy, by fostering low-carbon strategies that retain liquid and gaseous fuels for distributive uses of energy in transport, buildings, and industry. These strategies could also enable overall net carbon removal from the atmosphere, if at some future time the world desires to reduce the global concentration of carbon dioxide. The task force considered only technologies that have the potential to achieve reductions on the scale of one billion metric tons of CO2 per year, which represents about 2.5 percent of annual global emissions (about 40 billion metric tons today). Arun Majumdar, a Stanford University professor who chaired the Task Force of the Secretary of Energy Advisory Board, said that research avenues at such a large scale could potentially include utilizing agricultural crops to store more carbon in the soil, re-using carbon dioxide to form plastics and fuels, and storing carbon dioxide in massive underground reservoirs while producing some fuels. "We are excited to have been able to provide the first steps toward a coherent strategy of research opportunities," Majumdar said. "The range of options that are ripe for research is truly impressive." The task force, made up of participants from eight universities, focused on entire systems. In one example, plants are modified to increase their efficiency in capturing carbon dioxide from the atmosphere during photosynthesis and to develop deeper roots to store the carbon in the soil. By the end of the process, the atmosphere has been scrubbed of the carbon dioxide, and carbon has been transferred from the atmosphere to the soil. Sally Benson, a Stanford professor and a task force member, said a great deal of research is still needed on this process and others included in the report. "Each of the strategies we reviewed has its own research frontier," she said. Because these strategies rely on industry-level solutions such as removing carbon dioxide at the smokestack or changing farming methods to retain carbon in the soil, they require development of new technology and new industrial processes. "The need is urgent, and we must develop and use multiple strategies to combat climate change," said task force member Emily A. Carter, dean of the School of Engineering and Applied Science and founding director of the Andlinger Center for Energy and the Environment at Princeton University. "But pursuing these research avenues will benefit not just climate change. As we have seen for more than a century, investment in science and engineering research pays off in new technologies, new industries, jobs, and societal benefits far beyond the initial expense and in ways we cannot predict." The task force recommendations were delivered in a report to Energy Secretary Ernest J. Moniz on Dec. 13, 2016. John Deutch, an emeritus professor and former provost at the Massachusetts Institute of Technology and the chair of the Secretary of Energy Advisory Board, said in a letter to Moniz that the report "has painted a scientifically interesting agenda for decarbonization that should be of interest to the scientific community writ large." The task force - made up of experts from Duke, Harvard, Georgia Tech, MIT, Princeton, Stanford, University of Illinois and Washington University, as well as a former official from ExxonMobil - cautioned that the development of systems to reduce CO2 emissions at such a scale would be difficult and complex. The members also said some of the techniques could have unexpected outcomes and urged the government to invest in research to evaluate the impacts of the technologies, both intended and unintended, beyond their ability to reduce atmospheric CO2. Taking steps to reduce atmospheric CO2 would require broad cooperation between academic researchers, government and policy leaders, and industry, the report concluded. An appendix to the report analyzes the flow of technology from labs to society and found all of these groups play a critical role in the development of new technology. The task force made five recommendations about research and development: - Improve and expand systems modeling. Members found that because of the complexity of large-scale CO2 reduction, improved models based on a systems approach are needed to evaluate impacts on the atmosphere, ecological systems, and the economy. - Harness the natural biological cycle in which plants absorb and store atmospheric CO2. There is a need to evaluate how to optimize crops to absorb greater amounts of carbon dioxide and store more carbon in the soil for long periods of time, without a major increase in needed resources such as water and fertilizer; how to promote agricultural techniques that extend the time that carbon remains in the soil; and how to use various biological resources, such as giant kelp, as a stock for biofuels. - Explore synthetic transformation of CO2 into useful fuels and products. Carbon dioxide can be converted to valuable chemicals and fuels but it requires energy to do so. A critical part of this system would be inexpensive carbon-free energy to drive this conversion. The task force recommended that the scientific community pursue research to explore better materials and systems that allow for reactions that would make CO2 conversion cheaper and more efficient. - Evaluate the storage of CO2 in geologic formations. Past work on enhanced oil recovery (EOR) focused on minimizing the storage of CO2 to extract hydrocarbons. The task force recommended developing advanced EOR where one would co-optimize CO2 storage and hydrocarbon extraction in such a way that substantially more carbon would be stored than is extracted in fossil fuels. - Study improved methods to separate and capture carbon dioxide from a mixture of gases, a process that is currently too expensive and energy intensive. Both discovery of improved substances to absorb carbon dioxide and development of processes able to separate and store carbon dioxide on a large scale are needed. Improved sorbents would reduce the cost of "direct air capture," which involves absorbing carbon dioxide directly from the air and concentrating it for use or storage. "Our report should help people appreciate the immense effort that will be required to reconfigure our energy system to make it sustainable in the face of climate change, geopolitical stability, and responsible use of land," said Robert Socolow, a professor emeritus of mechanical and aerospace engineering and co-director of the Carbon Mitigation Initiative at the Princeton Environmental Institute. "Our report provides a useful structure for addressing the pluses and minuses of several less familiar approaches."

van der Linden S.,Andlinger Center for Energy and the Environment | Maibach E.,George Mason University | Leiserowitz A.,Yale University
Perspectives on Psychological Science | Year: 2015

Despite being one of the most important societal challenges of the 21st century, public engagement with climate change currently remains low in the United States. Mounting evidence from across the behavioral sciences has found that most people regard climate change as a nonurgent and psychologically distant risk—spatially, temporally, and socially—which has led to deferred public decision making about mitigation and adaptation responses. In this article, we advance five simple but important “best practice” insights from psychological science that can help governments improve public policymaking about climate change. Particularly, instead of a future, distant, global, nonpersonal, and analytical risk that is often framed as an overt loss for society, we argue that policymakers should (a) emphasize climate change as a present, local, and personal risk; (b) facilitate more affective and experiential engagement; (c) leverage relevant social group norms; (d) frame policy solutions in terms of what can be gained from immediate action; and (e) appeal to intrinsically valued long-term environmental goals and outcomes. With practical examples we illustrate how these key psychological principles can be applied to support societal engagement and climate change policymaking. © 2015, The Author(s) 2015.

Shin I.,Princeton University | Carter E.A.,Andlinger Center for Energy and the Environment
International Journal of Plasticity | Year: 2014

The strength and ductility of metals are governed by the motion of dislocations, which is quantified by the Peierls stress (σp). We use orbital-free density functional theory (OFDFT) to characterize the motion of 13〈112̄0〉 dislocations on the basal {0001} and prismatic {11̄00} planes in hexagonal-close-packed magnesium (Mg) in order to understand its deformation mechanisms. We predict σp values of edge dislocations on the basal and prismatic planes to be 0.6 and 35.4 MPa, respectively. The presence of stable stacking faults only on the basal plane produces partial dislocation splitting, which significantly lowers σp for basal dislocations. Our atomic scale simulations reveal that dislocation mobility is strongly correlated with the number of core atoms moving collectively. OFDFT σp results are in excellent agreement with experiments (∼0.5 and 39.2 MPa), further validating OFDFT as an independent and predictive tool for simulating plastic behavior in main group metals at the mesoscale with first principles' accuracy. © 2014 Elsevier Ltd. All rights reserved.

Libisch F.,Vienna University of Technology | Huang C.,Los Alamos National Laboratory | Carter E.A.,Andlinger Center for Energy and the Environment
Accounts of Chemical Research | Year: 2014

ConspectusAb initio modeling of matter has become a pillar of chemical research: with ever-increasing computational power, simulations can be used to accurately predict, for example, chemical reaction rates, electronic and mechanical properties of materials, and dynamical properties of liquids. Many competing quantum mechanical methods have been developed over the years that vary in computational cost, accuracy, and scalability: density functional theory (DFT), the workhorse of solid-state electronic structure calculations, features a good compromise between accuracy and speed. However, approximate exchange-correlation functionals limit DFT's ability to treat certain phenomena or states of matter, such as charge-transfer processes or strongly correlated materials. Furthermore, conventional DFT is purely a ground-state theory: electronic excitations are beyond its scope. Excitations in molecules are routinely calculated using time-dependent DFT linear response; however applications to condensed matter are still limited.By contrast, many-electron wavefunction methods aim for a very accurate treatment of electronic exchange and correlation. Unfortunately, the associated computational cost renders treatment of more than a handful of heavy atoms challenging. On the other side of the accuracy spectrum, parametrized approaches like tight-binding can treat millions of atoms. In view of the different (dis-)advantages of each method, the simulation of complex systems seems to force a compromise: one is limited to the most accurate method that can still handle the problem size. For many interesting problems, however, compromise proves insufficient. A possible solution is to break up the system into manageable subsystems that may be treated by different computational methods. The interaction between subsystems may be handled by an embedding formalism.In this Account, we review embedded correlated wavefunction (CW) approaches and some applications. We first discuss our density functional embedding theory, which is formally exact. We show how to determine the embedding potential, which replaces the interaction between subsystems, at the DFT level. CW calculations are performed using a fixed embedding potential, that is, a non-self-consistent embedding scheme. We demonstrate this embedding theory for two challenging electron transfer phenomena: (1) initial oxidation of an aluminum surface and (2) hot-electron-mediated dissociation of hydrogen molecules on a gold surface. In both cases, the interaction between gas molecules and metal surfaces were treated by sophisticated CW techniques, with the remainder of the extended metal surface being treated by DFT. Our embedding approach overcomes the limitations of conventional Kohn-Sham DFT in describing charge transfer, multiconfigurational character, and excited states. From these embedding simulations, we gained important insights into fundamental processes that are crucial aspects of fuel cell catalysis (i.e., O2 reduction at metal surfaces) and plasmon-mediated photocatalysis by metal nanoparticles. Moreover, our findings agree very well with experimental observations, while offering new views into the chemistry. We finally discuss our recently formulated potential-functional embedding theory that provides a seamless, first-principles way to include back-action onto the environment from the embedded region. © 2014 American Chemical Society.

Isseroff L.Y.,Princeton University | Carter E.A.,Andlinger Center for Energy and the Environment
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We show that a "one-shot" GW approach (denoted G 0W 0) can accurately calculate the photoemission/inverse- photoemission properties of Cu 2O. As the results of any perturbative method are heavily dependent on the reference state, the appropriate reference Hamiltonian for G 0W 0 is identified by evaluating the performance of density-functional-theory-based input wave functions and eigenvalues generated with selected exchange-correlation functionals. It is shown that a reference Hamiltonian employing the hybrid Heyd-Scuseria-Ernzerhof functional used in conjunction with G 0W 0 produces an accurate photoemission/inverse-photoemission band gap and photoemission spectrum whose character is then further analyzed. The physical origin of why a hybrid functional is required for the zeroth-order wave function is discussed, giving insight into the unique electronic structure of Cu 2O in comparison to other transition-metal oxides. © 2012 American Physical Society.

News Article | February 23, 2017
Site: www.materialstoday.com

Just when lighting aficionados were in a dark place, light-emitting diodes (LEDs) came to the rescue. Over the past decade, LED technologies have swept the lighting industry by offering features such as durability, efficiency and long life. Now, engineering researchers at Princeton University have illuminated another path forward for LED technologies by refining the manufacturing of light sources made with crystalline substances known as perovskites. These offer a more efficient and potentially lower-cost alternative to the materials currently used to produce LEDs. The researchers have developed a technique in which nanoscale perovskite particles self-assemble to produce more efficient, stable and durable perovskite-based LEDs. This advance, reported in a paper in Nature Photonics, could speed the use of perovskite technologies in commercial applications such as lighting, lasers, and television and computer screens. "The performance of perovskites in solar cells has really taken off in recent years, and they have properties that give them a lot of promise for LEDs, but the inability to create uniform and bright nanoparticle perovskite films has limited their potential," said Barry Rand, an assistant professor of electrical engineering in the Andlinger Center for Energy and the Environment at Princeton. "Our new technique allows these nanoparticles to self-assemble to create ultra-fine grained films, an advance in fabrication that makes perovskite LEDs look more like a viable alternative to existing technologies," added Rand, who is the lead researcher on the paper. LEDs emit light when a voltage is applied across the LED. The resultant electrical current forces electrons from the negative side of the diode to the positive side, releasing energy in the form of light. LEDs operate best when the current can be strictly controlled. In Rand's devices, the thin nanoparticle-based films allowed just that. LEDs have many advantages over incandescent bulbs, including increased durability, longer life, smaller size, energy efficiency and low-heat. While they are still more expensive than fluorescent lights for room illumination, they are more energy efficient, light up faster and present fewer environmental concerns related to their disposal. Rand's team and others researchers are exploring perovskites as a potential lower-cost alternative to gallium nitride (GaN) and other materials currently used in LED manufacturing. Lower-cost LEDs would speed the acceptance of the bulbs, reducing energy use and environmental impacts. Perovskite is a mineral originally discovered in the mid-1800s in Russia and named in honor of the Russian mineralogist Lev Perovski. The term ‘perovskite’ extends to a class of compounds that share the crystalline structure of Perovski's mineral, a distinct combination of cuboid and diamond shapes. Perovskites exhibit a number of intriguing properties – they can be super-conductive or semi-conductive, depending on their structure – that make them promising materials for use in electrical devices. In recent years, they have been touted as a potential replacement for the silicon in solar panels, as they are cheaper to manufacture while offering equal efficiency as some silicon-based solar cells. Hybrid organic-inorganic perovskite layers are fabricated by dissolving perovskite precursors in a solution containing a metal halide and an organic ammonium halide. It is a relatively cheap and simple process that could offer an inexpensive alternative to conventional LEDs. But while the resulting semiconductor films can emit light in vivid colors, the crystals forming the molecular structure of the films are too large, which makes them inefficient and unstable. In their new paper, Rand and his team report that adding an additional type of organic ammonium halide –specifically, a long-chain ammonium halide – to the perovskite solution during production dramatically constrained the formation of crystals in the film. The resulting crystallites were much smaller (around 5–10nm across) than those generated with previous methods, and the halide perovskite films were far thinner and smoother. This led to better external quantum efficiency, meaning the LEDs emitted more photons per number of electrons entering the device. The films were also more stable that those produced by other methods. Russell Holmes, a professor of materials science and engineering at the University of Minnesota, said the Princeton research brings perovskite-based LEDs closer to commercialization. "Their ability to control the processing of the perovskite generated ultra-flat, nano-crystalline thin films suitable for high-efficiency devices," said Holmes, who was not involved in the research. "This elegant and general processing scheme will likely have broad application to other perovskite active materials and device platforms." This story is adapted from material from Princeton University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

Lessio M.,Andlinger Center for Energy and the Environment | Carter E.A.,Andlinger Center for Energy and the Environment
Journal of the American Chemical Society | Year: 2015

Experimental evidence suggests that pyridinium plays an important role in photocatalytic CO2 reduction on p-GaP photoelectrodes. Pyridinium reduction to pyridinyl has been previously proposed as an essential mechanistic step for this reaction. However, theoretical calculations suggest that this step is not feasible in solution. Here, cluster models and accurate periodic boundary condition calculations are used to determine whether such a reduction step could occur by transfer of photoexcited electrons from the p-GaP photocathode and whether this transfer could be catalyzed by pyridinium adsorption on the p-GaP surface. It is found that both the transfer of photoexcited electrons to pyridinium and pyridinium adsorption are not energetically favored, thus making very unlikely pyridinium reduction to the pyridinyl radical and the proposed mechanisms requiring this reduction step. Given this conclusion, an alternative and energetically viable pathway for pyridinium reduction on p-GaP photoelectrodes is proposed. This pathway leads to the formation of adsorbed species that could react to form adsorbed dihydropyridine, which was proposed previously to play the role of the active catalyst in this system. © 2015 American Chemical Society.

Keith J.A.,Andlinger Center for Energy and the Environment | Carter E.A.,Andlinger Center for Energy and the Environment
Journal of the American Chemical Society | Year: 2012

The role of pyridinium cations in electrochemistry has been believed known for decades, and their radical forms have been proposed as key intermediates in modern photoelectrocatalytic CO 2 reduction processes. Using first-principles density functional theory and continuum solvation models, we have calculated acidity constants for pyridinium cations and their corresponding pyridinyl radicals, as well as their electrochemical redox potentials. Contrary to previous assumptions, our results show that these species can be ruled out as active participants in homogeneous electrochemistry. A comparison of calculated acidities and redox potentials indicates that pyridinium cations behave differently than previously thought, and that the electrode surface plays a critical (but still unknown) role in pyridinium reduction. This work substantially alters the mechanistic view of pyridinium-catalyzed photoelectrochemical CO 2 reduction. © 2012 American Chemical Society.

Isseroff L.Y.,Andlinger Center for Energy and the Environment | Carter E.A.,Andlinger Center for Energy and the Environment
Chemistry of Materials | Year: 2013

Cuprous oxide (Cu2O) is an attractive material for solar energy applications, but its photoconductivity is limited by minority carrier recombination caused by native defect trap states. We examine the creation of trap states by cation vacancies, using first principles calculations based on density functional theory (DFT) to analyze the electronic structure and calculate formation energies. With several DFT-based methods, a simple vacancy is predicted to be consistently more stable than a split vacancy by 0.21 ± 0.03 eV. Hybrid DFT is used to analyze the density of states and charge density distribution, predicting a delocalized hole for the simple vacancy and a localized hole for the split vacancy, in contrast to previously reported results. The differing character of the two defects indicates that they contribute to conduction via different mechanisms, with the split vacancy as the origin of the acceptor states that trap minority carriers. We explore methods of improving photoconductivity by doping Cu2O with Li, Mg, Mn, and Zn, analyzing their impact on vacancy formation energies and electronic structures. Results suggest that the Li dopant has the greatest potential to improve the photoconductivity of the oxide by inhibiting the creation of trap states. © 2013 American Chemical Society.

Keith J.A.,Andlinger Center for Energy and the Environment | Carter E.A.,Andlinger Center for Energy and the Environment
Journal of Chemical Theory and Computation | Year: 2012

Sensibly modeling (photo)electrocatalytic reactions involving proton and electron transfer with computational quantum chemistry requires accurate descriptions of protonated, deprotonated, and radical species in solution. Procedures to do this are generally nontrivial, especially in cases that involve radical anions that are unstable in the gas phase. Recently, pyridinium and the corresponding reduced neutral radical have been postulated as key catalysts in the reduction of CO 2 to methanol. To assess practical methodologies to describe the acid/base chemistry of these species, we employed density functional theory (DFT) in tandem with implicit solvation models to calculate acidity constants for 22 substituted pyridinium cations and their corresponding pyridinyl radicals in water solvent. We first benchmarked our calculations against experimental pyridinium deprotonation energies in both gas and aqueous phases. DFT with hybrid exchange-correlation functionals provide chemical accuracy for gas-phase data and allow absolute prediction of experimental pK as with unsigned errors under 1 pK a unit. The accuracy of this economical pK a calculation approach was further verified by benchmarking against highly accurate (but very expensive) CCSD(T)-F12 calculations. We compare the relative importance and sensitivity of these energies to selection of solvation model, solvation energy definitions, implicit solvation cavity definition, basis sets, electron densities, model geometries, and mixed implicit/explicit models. After determining the most accurate model to reproduce experimentally-known pK as from first principles, we apply the same approach to predict pK as for radical pyridinyl species that have been proposed relevant under electrochemical conditions. This work provides considerable insight into the pitfalls using continuum solvation models, particularly when used for radical species. © 2012 American Chemical Society.

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