American Physical Society March Meeting (Baltimore, MD)

  • Baltimore Convention Center 1 W Pratt St Baltimore, MD 21201 United States

Bryan Beckingham and Daniel Miller, "Quantitative Monitoring of Membrane Permeation via In-Situ ATR FT-IR Spectroscopy"

Abstract: Ion conducting membranes are of interest for various energy applications including fuel cells and artificial photosynthesis systems. Within the context of artificial photosynthesis, membranes are desired that facilitate the ion transport necessary to feed the electrochemical reactions while meeting various additional selectivity and permeability demands depending on the CO2 reduction products. Herein, we demonstrate the use of in-situ ATR FT-IR spectroscopy to quantitatively resolve the concentration of single and multicomponent mixtures of various CO2 reduction products including methanol, formate and acetate. We then apply this methodology to the in-situ monitoring of the permeation of single and multicomponent mixtures across commercially available membranes. Membrane permeabilities and selectivities calculated from the single component time-resolved concentration curves are compared to the multicomponent permeation experiments.

Jeffrey Neation, "High-Throughput Discovery of Electrochemically Stable Photocatalysts for Oxygen Evolution"

Abstract: Widespread use of artificial photosynthesis hinges upon development of photocatalysts and light absorbers with excellent electrochemical stability in aqueous solution. The poor stability of most semiconductors in the highly oxidizing environment of a solar fuels photoanode has been a key factor limiting the use of many candidates light absorbers. We assess the stability of candidate transition metal oxides (TMOs) in alkaline aqueous environments from calculated Pourbaix diagrams. Our analysis reveals interesting trends in the electrochemical stability of TMOs containing elements which have not traditionally been explored for photocatalysts. Utilizing the Pourbaix diagram analysis as the first screen-layer in a high-throughput workflow that incorporates automating density functional theory and hybrid functional calculations, we screen for electrochemically stable TMO compounds with low band gaps and optimal band edge energies. Applying our new data-driven approach, we successfully identify several new TMOs with promising band gaps and edges that are predicted to resist corrosion under aqueous conditions relevant to solar water splitting. Materials synthesis and electrochemical measurements confirm several predictions and demonstrate the utility of computational screening for identifying new solar fuels materials.

Jeffrey Neaton, "Composition-Dependent Phase Concentrations from First Principles: Simulating Combinatorial Libraries of Transition Metal Oxides"

Abstract: To identify material phases in experimental combinatorial libraries, we develop a theoretical model as a complementary approach to accelerate phase identification. In this approach, samples in a combinatorial library are simulated as mixtures in chemical equilibria. Each of these mixtures contains all the solid-state phases, which can possibly exist in the library. Using the total energies of these phases obtained in first-principle calculations, we calculate the Gibbs free energy changes in the corresponding chemical reactions, and subsequently evaluate the equilibrium concentrations of the phases in every sample according to the law of mass action. Furthermore, to test this approach, we simulate pseudobinary libraries MnxV1-xOy and CuxV1-xOy. Interestingly, we find  that the composition-dependent phase concentrations calculated within our approach agree well with the experimental results measured with XRD spectroscopy.

Ravishankar Sundararaman, "Excited Carrier Dynamics and Transport in Plasmonic Nanostructures"

Abstract: Surface plasmon resonances provide a pathway to efficiently capture electromagnetic radiation in sub-wavelength structures for energy conversion and photodetection at the nano scale. The complete mechanism involves several microscopic steps spanning length scales from atomic dimensions to tens or hundreds of nanometers, posing challenges for experimental characterization and for first-principles predictions. To provide the basis for predicting and optimizing the complex interplay of materials and geometric effects in plasmon decay-induced excited carrier phenomena, we combined \emph{ab initio} electronic structure calculations, electromagnetic simulations and Boltzmann transport models. In Au, Ag, Cu and Al nanostructures, we find that initial carrier distributions as well as their subsequent transport, relaxation and thermalization are sensitive to electronic structure, exhibiting strong asymmetries between electrons and holes. We predict energy-dependent spatially-resolved carrier distributions collected in plasmonic nanostructures with strong field inhomogeneities, and explore the possibility of tailoring materials and geometry to collect the carrier distributions needed for such applications as photochemically driven CO2 reduction and water splitting.

Qimin Yan, "First-Principles Data-Driven Discovery of Transition Metal Oxides for Artificial Photosynthesis"

Abstract: We develop a first-principles data-driven approach for rapid identification of transition metal oxide (TMO) light absorbers and photocatalysts for artificial photosynthesis using the Materials Project. Initially focusing on Cr, V, and Mn-based ternary TMOs in the database, we design a broadly-applicable multiple-layer screening workflow automating density functional theory (DFT) and hybrid functional calculations of bulk and surface electronic and magnetic structures. We further assess the electrochemical stability of TMOs in aqueous environments from computed Pourbaix diagrams. Several promising earth-abundant low band-gap TMO compounds with desirable band edge energies and electrochemical stability are identified by our computational efforts and then synergistically evaluated using high-throughput synthesis and photoelectrochemical screening techniques by our experimental collaborators at Caltech. Our joint theory-experiment effort has successfully identified new earth-abundant copper and manganese vanadate complex oxides that meet highly demanding requirements for photoanodes, substantially expanding the known space of such materials. By integrating theory and experiment, we validate our approach and develop important new insights into structure-property relationships for TMOs for oxygen evolution photocatalysts, paving the way for use of first-principles data-driven techniques in future applications. This work is supported by the Materials Project Predictive Modeling Center and the Joint Center for Artificial Photosynthesis through the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231. Computational resources also provided by the Department of Energy through the National Energy Supercomputing Center.