PacSurf2018 Session EH-TuP: Energy Harvesting and Storage Poster Session
Tuesday, December 4, 2018 4:00 PM in Room Naupaka Salon 1-3
EH-TuP-1 Oxygen Vacancies Boost δ-Bi2O3 as High-Performance Electrode for Rechargeable Aqueous Batteries
TingTing Qin, Wei Zhang (State Key Laboratory of Automotive Simulation and Control, and School of Materials Science & Engineering, and Electron Microscopy Center, and International Center of Future Science, Jilin University, Changchun 130012, China)
Metal oxides as electrode materials are of great potential for rechargeable aqueous batteries. However，they suffer from inferior cycle stability and rate capability because of poor electronic and ionic conductivities. Herein, taking vertically-orientated Bi2O3 nanoflakes on Ti substrates as examples, we found that δ-Bi2O3 electrode with plenty of intrinsic positively-charged oxygen defects have shown remarkably higher specific capacity (264 mAh g-1) and far superior rate capability than that of α -Bi2O3 with less oxygen vacancies . Through pinpointing the existence form and the role of oxygen vacancies within the electrochemical processes, we demonstrate that oxygen vacancies in δ-Bi2O3 serve as central entrepots collecting OHˉ groups via electrostatic force effect, which has boosted the oxidation reaction and enhanced the electrochemical properties. Besides, oxygen vacancies can largely facilitate electronic conductivity. Our work merited an excellent Bi2O3 negative electrode material via giving full play to the role of oxygen vacancies in electrochemical energy storage.View Supplemental Document
EH-TuP-3 Novel Cathode Nanomaterials and Electrolytes for Al-ion Batteries
Nicolò Canever (Victoria University of Wellington, New Zealand); Nicolas Bertrand (Ecole Nationale Supérieure de Chimie de Clermont-Ferrand, SIGMA Clermont, Aubière,France); Thomas Nann (Victoria University of Wellington, New Zealand)
Battery-based energy storage could be a useful tool for transitioning to a fully renewable-based energy economy. Current battery technologies, however, often lack the cost-effectiveness  and safety  requirements necessary for large-scale grid energy storage applications. Aluminium-ion batteries (AIBs) are a very promising alternative to Lithium-based systems, thanks to the low cost, non-flammability, and three-electron redox chemistry of aluminium.  AIBs could, in principle, offer better cost-effectiveness, energy density  and safety,  than currently available energy storage technologies. This poster deals with the investigation of new electrode nanomaterials and electrolyte systems for Al-ion batteries, with the aim of improving the performance and cost-effectiveness of AIBs, and facilitate their commercial feasibility.
 Delucchi, M. A.; Jacobson, M. Z. Energy Policy 2011, 39 (3), 1170.
 Barnes, F. S.; Levine, J. G. Large energy storage systems handbook; CRC press, 2011.
 K. Das, S.; Mahapatra, S.; Lahan, H. J. Mater. Chem. A 2017, 5 (14), 6347.
 Jayaprakash, N.; Das, S. K.; Archer, L. A. Chem. Commun. 2011, 47 (47), 12610.
 Lin, M.-C.; Gong, M.; Lu, B.; Wu, Y.; Wang, D.-Y.; Guan, M.; Angell, M.; Chen, C.; Yang, J.; Hwang, B.-J.; Dai, H. Nature 2015, 520 (7547), 324.
EH-TuP-4 Study of Charge Transfer across C60/BCP and BCP/Ag Interfaces Using Core-Hole Clock Spectroscopy
Tetsuya Miyazawa (SOKENDAI, Japan); Kenichi Ozawa (Tokyo Institute of Technology, Japan); Kaname Kanai (Tokyo University of Science, Japan); Takeaki Sakurai (Tsukuba University, Japan); Kazuhiko Mase (KEK, Japan)
Electronic properties at organic/metal and organic/organic interfaces affect the efficiencies of organic electronic devices such as organic solar cells, perovskite solar cells, and organic field effect transistors. Peuman et al. have found that the conversion efficiency of the organic solar cell is improved when bathocuproine (BCP) is inserted as buffer layer between the organic molecule of acceptor and negative electrode [P. Peuman et al., Appl. Phys. Lett. 76, 2650 (2000).]. In order to reveal the role of buffer layers, we investigated C60/BCP and BCP/Ag layered systems by resonant photoelectron spectroscopy and X-ray absorption spectroscopy. A core-hole clock analysis was carried out to examine transfer times of an electron from C60 to BCP and that from BCP to Ag. The sample was prepared by the procedure that monolayer of BCP was deposited on Ag thin film and then monolayer of C60 was deposited on the BCP. The charge transfer times from LUMO+1 of BCP to Ag and C60 to BCP were calculated to be 2.5 fs and less than 60 fs, respectively. In the photoelectric conversion of organic solar cells, electrons generated by exciton separation transfer from organic molecule of acceptor to negative electrode. These results suggest that ultrafast charge transfers across C60 to BCP and BCP to Ag are one of the role of buffer layers to improve conversion efficiency of organic solar cells. View Supplemental Document
EH-TuP-6 Structure and Optical Properties of HfO2-based Thermal Emitter Films for Thermophotovoltaic Energy Conversion Devices
Gregory Abadias, Youssef Metayrek, Anny Michel, Jérémie Drevillon (Institut Pprime, CNRS-Université de Poitiers, France)
One of the key points for designing high-efficiency thermophotovoltaic (TPV) systems is to match the spectral emission of the radiator with the spectral range where photons are converted into electron-hole pairs inside the photovoltaic device. Recent studies have shown the potential offered by photonic crystals made of metal/dielectric stack of layers acting as Fabry-Pérot cavity, ensuring spectral selectivity to the emitter. Another material requirement is thermal stability in order to keep the same spectral emission at the operating temperature of the radiator. The Mo/HfO2 system is a promising candidate material in this respect, as recently reported by Blandre et al. .
In this work we investigate the synthesis by magnetron sputtering of W/HfO2 four-layer films for TPV applications. The individual layer thicknesses were optimized based on fluctuational electrodynamics calculations of thermal emissivity of one-dimensional layered media. Prior to the fabrication of the multilayer stack, the structure and optical properties of the transparent HfO2 layer were investigating as a function of process parameters: substrate temperature Ts and O2 flow rate.Films were characterized by X-ray reflectivity, X-ray diffraction and wavelength dispersive spectroscopy. The optical indices (n and k) were measured experimentally from variable angle spectroscopic ellipsometry in the visible and mid-infrared (MIR) range (up to 35 μm). Results show that dense, crystalline HfO2 layers with monoclinic structure can be formed by reactive magnetron sputtering at room temperature with optical index n close to 2.1 at 550 nm; however, crystallinity was improved by increasing Ts up to 500°C, with little variation on n and k. In the MIR, the optical properties of HfO2 were consistent with the data reported by Bright et al. .The optical reflectance of the W/HfO2 stack was measured using spectrophotometer and a good agreement with theoretical predictions was found, attesting of the potential of this system for TPV emitters.
EH-TuP-7 Bimetallic Cobalt-Iron Hydroxide Encapsulated in Organic Ligand Derived Carbon Layers as an Efficient Electrocatalyst for Oxygen Evolution Reaction
Jian Du, Fei Li (Dalian University of Technology, China)
Water electrolysis as one of the prospective approach to produce hydrogen is limited by the anodic oxygen evolution reaction (OER) due to its sluggish kinetics. Considering the practical application, the development of highly efficient non-noble OER catalysts is essential. Among the reported low-cost electrocatalysts, CoFe-based oxides or hydroxides are intriguing owing to the rich redox chemistry. However, the severe aggregation and intrinsically poor electronic conductivity hinder their electrocatalytic performance. Hybridizing cobalt-iron oxides or hydroxides with carbon materials can not only enhance the conductivity of the catalyst, but also facilitate the uniform distribution of metal species within carbon matrix, thus improving the electrochemical performance towards OER. In view of this, we report here the bimetallic cobalt-iron hydroxide encapsulated in carbon layers derivedfrom organic ligand (Schiff base) via hydrothermal carbonization. In alkaline media, Co Fe/C loaded on GC electrode delivers a current density of 10 mA cm-2 at an overpotential of 260 mV and exhibits a low Tafel slope of 45.2 mV dec-1 as well as excellent durability. The remarkable OER performance outperforms those of CoFe-based electrocatalyst in the literature.
Keywords: Oxygen evolution reaction, cobalt-iron hydroxide, organic ligand, electrocatalyst
As shown in Figure 1, the Co1.2Fe/C delivers a current density of 10 mA cm-2 at an overpotential of 260 mV and exhibits a low Tafel slope of 45.2 mV dec-1 as well as excellent durability in 1M KOH solution.
Figure 1 (a) LSV curves of GC, Co1.2Fe and Co1.2Fe/C; (b) Tafel plots of Co1.2Fe and Co1.2Fe/C; © Chronopotentiometric measurement of Co1.2Fe/C at 10 mA cm-2. All tests were carried out in 1 M KOH.
The Co1.2Fe/C exhibits excellent OER performance in alkaline media, which can be ascribed to the following factors: 1) the homogenous distribution of metal hydroxide within carbon matrix inhibits the aggregation of the active nanoparticles; 2) the excellent electronic conductivity enables fast electron transport during the OER process; 3) the synergetic effect between the Co1.2Fe hydroxide and carbon species also contributes to the improvement of the electrochemical performance.
 S. Yin, W. Tu, Y. Sheng, Y. Du, M. Kraft, A. Borgna, R. Xu, Adv. Mater. 2017, 1705106.
 F. Li, J. Du, X. Li, J. Shen, Y. Wang, Y, Zhu, L. Sun, Adv. Energy Mater. 2018, 1702598.
EH-TuP-8 Anchoring Water Oxidation Catalysts on a DS-PEC via Pyridine Group for Light-Driven Water Splitting
Yong Zhu, Fei Li (Dalian University of Technology, China); Licheng Sun (KTH Royal Institute of Technology, Sweden)
Dye-sensitized photoelectrochemical cell (DS-PEC) water splitting into hydrogen and oxygen is a potential approach to realize the conversion solar energy to chemical energy efficiently. Ru(bda) (bda is 2,2`-bipyridine-6,6`-dicarboxylate) is one of the most efficient water oxidation catalysts in DS-PEC. Traditionally, Ru(bda) have been anchored onto the dye-sensitized photoanode by modifying phosphoric acid or carboxylic acid groups. These complexes can reduce the overpotentials of water oxidation and exhibit highest turnover. However, the efficiency of the entire system is inhibited due to the strong recombination effect of electrons injected into theTiO2 bulk on the photosensitizer and catalyst in the oxidized state. Herein, we have replaced the anchor group of the water oxidation catalysts Ru(bda) (bda is 2,2′bipyridine-6,6′-dicarboxylate) from phosphoric acid to pyridine. Time-resolved transient absorption spectroscopy demonstrates that the pyridine anchor group have effect of inhibiting electron recombination. The photocurrent densities of 1.5-1.8 mA/cm2 were achieved and produced an incident photon to current efficiency (IPCE) of 25.5% at 450 nm. Under pH=5.8 under 100mW/cm2 (>400nm) illumination.
EH-TuP-9 On the Thermal Characterization of Heptane-Isooctane Mixtures
Adrian Bedoya, Ernesto Marin, Salvador Alvarado (Cicata Legaria, Mexico)
The thermal transport properties of heptane-isooctane mixtures in the liquid phase at room temperature and atmospheric pressure were measured and calculated. The thermal conductivity, k, was measured using the transient hot-wire (HW) method, and the thermal effusivity, e, was determined by the front photopyroelectric (FPPE) technique. Then, the thermal diffusivity, α, and the volume specific heat capacity (heat capacity per unit volume), C, were calculated using the well-known relationships α = (k/e)2 and C = e2/k , respectively. We show that a correlation between these parameters and octane number exists, and that the obtained thermal parameters proved to be sensitive to detect molecular associations in binary hydrocarbon liquid mixtures. We also report about the thermal conductivity of mixtures of n-alkanes vapors and air showing that almost similar values are obtained for heptane and isooctane, so that octane number rating using the well-established binary mixtures of these substances becomes impossible with thermal properties measurements in the gas phase.
EH-TuP-10 A steady-state thermoreflectance method to measure thermal conductivity
Jeffrey Braun, David Olson, John Gaskins, Patrick Hopkins (University of Virginia)
We demonstrate a steady-state thermoreflectance based optical pump-probe technique to measure the thermal conductivity of materials using a continuous wave laser heat source. The technique works in principle on leaving a pump laser on long enough to induce a steady-state temperature rise in a material. A probe beam is then used to detect the resulting change in reflectance, which is proportional to the change in temperature of the sample. Varying the power of the pump beam to induce larger temperature rises, Fourier’s law is used to determine the thermal conductivity. We show that this technique is capable of measuring the thermal conductivity of a wide range of materials having thermal conductivities ranging from 1 to > 2000 W m−1K−1, in excellent agreement to literature values. With a measurement length scale capable of reaching <10 microns, this techniques is capable of measuring both bulk material and films.