• Energy Research

Black carbon (BC) may play an important role in the global C budget, due to its potential to act as a significant sink of atmospheric CO2. In order to fully evaluate the influence of BC on the global C cycle, an understanding of the stability of BC is required. The biochemical stability of BC was assessed in a chronosequence of high-BC-containing Anthrosols from the central Amazon, Brazil, using a range of spectroscopic and biological methods. Results revealed that the Anthrosols had 61–80% lower (P 0.05) difference in CO2 respiration per unit C was observed between Anthrosols with contrasting ages of BC (600–8700 years BP) and soil textures (0.3–36% clay). Similarly, the molecular composition of the core regions of micrometer-sized BC particles quantified by synchrotron-based Near-Edge X-ray Fine Structure (NEXAFS) spectroscopy coupled to Scanning Transmission X-ray Microscopy (STXM) remained similar regardless of their ages and closely resembled the spectral characteristics of fresh BC. BC decomposed extremely slowly to an extent that it was not possible to detect chemical changes between youngest and oldest samples, as also confirmed by X-ray Photoelectron Spectroscopy (XPS). Deconvolution of NEXAFS spectra revealed greater oxidation on the surfaces of BC particles with little penetration into the core of the particles. The similar C mineralization between different BC-rich soils regardless of soil texture underpins the importance of chemical recalcitrance for the stability of BC, in contrast to adjacent soils which showed the highest mineralization in the sandiest soil. However, the BC-rich Anthrosols had higher proportions (72–90%) of C in the more stable organo-mineral fraction than BC-poor adjacent soils (2–70%), suggesting some degree of physical stabilization.

We report on the preparation and detailed characterization of ferromagnetic (FM) Zn 1-x Cr x O thin films deposited on Si substrates using reactive co-sputtering of Cr and Zn in controlled oxygen atmosphere. X-ray diffraction (XRD) data showed wurtzite ZnO peaks in the FM films prepared with lower Cr sputter powers, whose position and intensities are influenced by Cr doping. However, samples prepared with higher Cr powers did not show ferromagnetism but displayed evidence of Cr 2 O 3 and ZnCr 2 O 4 phases with no zinc oxide (ZnO) phase. The magnetization is higher (saturation magnetization M s = 18 emu/cm 3 ) for lower Cr concentrations and decreases for higher Cr doping. The samples were investigated extensively to understand the film composition, dopant distribution, homogeneity and potential origin of the observed ferromagnetism. Particle-induced X-ray emission (PIXE) studies were employed to determine the chemical composition as well as the Cr/Zn ratio in the films. Film uniformity and homogeneity, investigated using Rutherford backscattering spectrometry, showed a relatively uniform ZnO layer in the as-prepared samples but, in a sample annealed at 800°C, showed some diffusion of Si from the substrate. X-ray photoelectron spectroscopy (XPS) studies indicated that Cr ions are in the oxidized state, but showed changes in the binding energy and Cr concentration when measured after removing 10 nm from the surface using Ar ion sputtering. Possible origins of the observed FM behavior are discussed based on the comprehensive characterization results.

Electrocatalysis of oxygen reduction using Pt nanoparticles supported on functionalized graphene sheets (FGSs) was studied. FGSs were prepared by thermal expansion of graphite oxide. Pt nanoparticles with average diameter of 2 nm were uniformly loaded on FGSs by impregnation methods. Pt-FGS showed a higher electrochemical surface area and oxygen reduction activity with improved stability as compared with the commercial catalyst. Transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical characterization suggest that the improved performance of Pt-FGS can be attributed to smaller particle size and less aggregation of Pt nanoparticles on the functionalized graphene sheets.

We report on synthesis and functional properties of ultrathin oxide layers synthesized on metal surfaces by room temperature photon irradiation. We show that the impedance of a passive aluminum oxide film synthesized under ultraviolet photon irradiation is an order of magnitude larger than that of native oxide in a 0.5M NaCl solution. Further, the structure and impedance of existing native oxide layers can be dramatically improved by minutes-long exposure to photon irradiation. Depth profiling studies with x-ray photoelectron spectroscopy shows that chlorine uptake in UV-synthesized oxides, compared to that of native oxides, is reduced which can contribute to the improvement in corrosion resistance. The results are of significance to synthesis of ultrathin passive layers on metal and alloy structures for environmental protection.

Abstract Highly-oriented pure and gadolinia-doped ceria thin films have been grown on pure and zirconia (ZrO 2 ) (111)-buffered sapphire (Al 2 O 3 ) (0001) substrates using oxygen plasma-assisted molecular beam epitaxy to understand the oxygen ionic transport processes in ceria based oxide thin films. Gadolinia-doped ceria films grown on sapphire substrate show polycrystalline features due to structural deformations resulting from the large lattice mismatch between the Al 2 O 3 (0001) substrate and the ceria films. In contrast, the films, grown on a thin layer of ZrO 2 (111) buffered sapphire substrate, appear to be highly oriented in nature with predominant double domain (111) orientation. Oxygen ionic conductivity of these gadolinia-doped ceria films was measured as a function of gadolinium concentration and found to be efficient at relatively lower temperature operation compared to that of bulk polycrystalline, single crystalline yttria stabilized zirconia and gadolinia-doped polycrystalline ceria. Relative improvement in ionic conductivity of highly oriented gadolinia-doped ceria films (in the lower temperature regime) can be ascribed to the increased oxygen vacancies due to presence of Gd as well as high quality of the oriented thin films.

Solid oxide fuel cells (SOFCs) are presently being developed for gasification integrated power plants that generate electricity from coal at 50+% efficiency. The interaction of trace metals in coal syngas with the Ni-based SOFC anodes is being investigated through thermodynamic analyses and in laboratory experiments, but direct test data from coal syngas exposure are sparsely available. This research effort evaluates the significance of SOFC performance losses associated with exposure of a SOFC anode to direct coal syngas. SOFC specimen of industrially relevant composition are operated in a unique mobile test skid that was deployed to the research gasifier at the National Carbon Capture Center (NCCC) in Wilsonville, AL. The mobile test skid interfaces with a gasifier slipstream to deliver hot syngas (up to 300°C) directly to a parallel array of 12 button cell specimen, each of which possesses an active area of approximately 2 cm2. During the 500 hour test period, all twelve cells were monitored for performance at four discrete operating current densities, and all cells maintained contact with a data acquisition system. Of these twelve, nine demonstrated good performance throughout the test, while three of the cells were partially compromised. Degradation associated with the properly functioning cells wasmore » attributed to syngas exposure and trace material attack on the anode structure that was accelerated at increasing current densities. Cells that were operated at 0 and 125 mA/cm² degraded at 9.1 and 10.7% per 1000 hours, respectively, while cells operated at 250 and 375 mA/cm² degraded at 18.9 and 16.2% per 1000 hours, respectively. Post-trial spectroscopic analysis of the anodes showed carbon, sulfur, and phosphorus deposits; no secondary Ni-metal phases were found.« less

Lithium (Li) pulverization and associated large volume expansion during cycling is one of the most critical barriers for the safe operation of Li-metal batteries. Here, we report an approach to minimize the Li pulverization using an electrolyte based on a fluorinated orthoformate solvent. The solid–electrolyte interphase (SEI) formed in this electrolyte clearly exhibits a monolithic feature, which is in sharp contrast with the widely reported mosaic- or multilayer-type SEIs that are not homogeneous and could lead to uneven Li stripping/plating and fast Li and electrolyte depletion over cycling. The highly homogeneous and amorphous SEI not only prevents dendritic Li formation, but also minimizes Li loss and volumetric expansion. Furthermore, this new electrolyte strongly suppresses the phase transformation of the LiNi0.8Co0.1Mn0.1O2 cathode (from layered structure to rock salt) and stabilizes its structure. Tests of high-voltage Li||NMC811 cells show long-term cycling stability and high rate capability, as well as reduced safety concerns. Parasitic reactions between Li metal and electrolytes need to be mitigated in Li-metal batteries. Here, the authors report the use of a fluorinated orthoformate-based electrolyte, leading to a monolithic solid–electrolyte interphase and subsequently a high-performance Li-metal battery.

The key to enabling long-term cycling stability of high-voltage lithium (Li) metal batteries is the development of functional electrolytes that are stable against both Li anodes and high-voltage (above 4 V versus Li/Li+) cathodes. Due to their limited oxidative stability ( 90% over 300 cycles and ~80% over 500 cycles with a charge cut-off voltage of 4.3 V. This study offers a promising approach to enable ether-based electrolytes for high-voltage Li metal battery applications. Ether-based electrolytes offer many advantages compared to other electrolyte systems, but they are not stable in Li metal batteries when operating at high voltages. Here, the authors develop a concentrated ether electrolyte that enables long-term cycling stability of high-voltage Li metal batteries.

Batteries using lithium (Li) metal as anodes are considered promising energy storage systems because of their high energy densities. However, safety concerns associated with dendrite growth along with limited cycle life, especially at high charge current densities, hinder their practical uses. Here we report that an optimal amount (0.05 M) of LiPF6 as an additive in LiTFSI–LiBOB dual-salt/carbonate-solvent-based electrolytes significantly enhances the charging capability and cycling stability of Li metal batteries. In a Li metal battery using a 4-V Li-ion cathode at a moderately high loading of 1.75 mAh cm−2, a cyclability of 97.1% capacity retention after 500 cycles along with very limited increase in electrode overpotential is accomplished at a charge/discharge current density up to 1.75 mA cm−2. The fast charging and stable cycling performances are ascribed to the generation of a robust and conductive solid electrolyte interphase at the Li metal surface and stabilization of the Al cathode current collector. Deployment of rechargeable Li metal batteries requires fast charging capability and long-term cycling stability. Here the authors demonstrate the battery application potential of using a small amount of LiPF6 in a dual-salt electrolyte.