The drawbacks of common anodes in lithium-ion batteries (LIBs) and hybrid supercapacitors (HSCs), such as the high voltage plateau of Li4Ti5O12(1.55 V vs. Li/Li+) and the moderate capacity of graphite (372 mAh-g-1), have established a need for better materials. Conversion materials, and in particular iron oxide and CaFe2O4(CFO), have amassed recent attention as potential anode replacements. In this study, we evaluate the material and electrochemical effects of the solution combustion synthesis (SCS) of porous CFO across novel fuel-to-oxidizer ratios and calcination temperatures. We demonstrate that nearly doubling the amount of fuel used during synthesis increases capacities between 120 and 150% at high current densities (~ 1000 mA-g-1) and across 500 additional charging-discharging cycles, an effect brought on in part by enhanced compositional purity in these samples. However, in order to ensure long-term cyclic stability, it is necessary to also calcine porous CFO to 900 °C to enhance crystallite size, particle size and spacing, and compositional purity.
- Publication Date:
- NSF-PAR ID:
- Journal Name:
- Scientific Reports
- Nature Publishing Group
- Sponsoring Org:
- National Science Foundation
More Like this
Advances in the synthesis and processing of graphene-based materials have presented the opportunity to design novel lithium-ion battery (LIB) anode materials that can meet the power requirements of next-generation power devices. In this work, a poly(methacrylic acid) (PMAA)-induced self-assembly process was used to design super-mesoporous Fe 3 O 4 and reduced-graphene-oxide (Fe 3 O 4 @RGO) anode materials. We demonstrate the relationship between the media pH and Fe 3 O 4 @RGO nanostructure, in terms of dispersion state of PMAA-stabilized Fe 3 O 4 @GO sheets at different surrounding pH values, and porosity of the resulted Fe 3 O 4 @RGO anode. The anode shows a high surface area of 338.8 m 2 g −1 with a large amount of 10–40 nm mesopores, which facilitates the kinetics of Li-ions and electrons, and improves electrode durability. As a result, Fe 3 O 4 @RGO delivers high specific-charge capacities of 740 mA h g −1 to 200 mA h g −1 at various current densities of 0.5 A g −1 to 10 A g −1 , and an excellent capacity-retention capability even after long-term charge–discharge cycles. The PMAA-induced assembly method addresses the issue of poor dispersion of Fe 3 O 4 -coatedmore »
Sr 1-x Ca x Fe 1-y Co y O 3-δ as facile and tunable oxygen sorbents for chemical looping air separation
Chemical looping air separation (CLAS) is a promising technology for oxygen generation with high efficiency. The key challenge for CLAS is to design robust oxygen sorbents with suitable redox properties and fast redox kinetics. In this work, perovskite-structured Sr1-xCaxFe1-yCoyO3oxygen sorbents were investigated and demonstrated for oxygen production with tunable redox properties, high redox rate, and excellent thermal/steam stability. Cobalt doping at B site was found to be highly effective, 33% improvement in oxygen productivity was observed at 500 °C. Moreover, it stabilizes the perovskite structure and prevents phase segregation under pressure swing conditions in the presence of steam. Scalable synthesis of Sr0.8Ca0.2Fe0.4Co0.6O3oxygen sorbents was carried out through solid state reaction, co-precipitation, and sol-gel methods. Both co-precipitation and sol-gel methods are capable of producing Sr0.8Ca0.2Fe0.4Co0.6O3sorbents with satisfactory phase purity, high oxygen capacity, and fast redox kinetics. Large scale evaluation of Sr0.8Ca0.2Fe0.4Co0.6O3, using an automated CLAS testbed with over 300 g sorbent loading, further demonstrated the effectiveness of the oxygen sorbent to produce 95% pure O2with a satisfactory productivity of 0.04 gO2gsorbent−1h−1at 600 °C.
Herein, we describe an atomic layer deposition (ALD) system that is optimized for the growth of thin films on high-surface-area, porous materials. The system incorporates a moveable dual-zone furnace allowing for rapid transfer of a powder substrate between heating zones whose temperatures are optimized for precursor adsorption and oxidative removal of the precursor ligands. The reactor can both be evacuated, eliminating the need for a carrier gas during precursor exposure, and rotated, to enhance contact between a powder support and the gas phase, both of which help us to minimize mass transfer limitations in the pores during film growth. The capabilities of the ALD system were demonstrated by growing La2O3, Fe2O3, and LaFeO3films on a 120 m2 g−1MgAl2O4powder. Analysis of these films using scanning transmission electron microscopy and temperature-programmed desorption of 2-propanol confirmed the conformal nature of the oxide films.
Transition metal oxides of the 4
dand 5 dblock have recently become the targets of materials discovery, largely due to their strong spin–orbit coupling that can generate exotic magnetic and electronic states. Here, we report the high-pressure synthesis of Lu2Rh2O7, a new cubic pyrochlore oxide based on 4 d5Rh4+, and characterizations via thermodynamic, electrical transport, and muon spin relaxation measurements. Magnetic susceptibility measurements reveal a large temperature-independent Pauli paramagnetic contribution, while heat capacity shows an enhanced Sommerfeld coefficient, γ= 21.8(1) mJ/mol-Rh K2. Muon spin relaxation measurements confirm that Lu2Rh2O7remains paramagnetic down to 2 K. Taken in combination, these three measurements suggest that Lu2Rh2O7is a correlated paramagnetic metal with a Wilson ratio of R W= 2.5. However, electric transport measurements present a striking contradiction as the resistivity of Lu2Rh2O7is observed to monotonically increase with decreasing temperature, indicative of a nonmetallic state. Furthermore, although the magnitude of the resistivity is that of a semiconductor, the temperature dependence does not obey any conventional form. Thus, we propose that Lu2Rh2O7may belong to the same novel class of non-Fermi liquids as the nonmetallic metal FeCrAs.
Review—Development of Highly Active and Durable Hybrid Compressive Platinum Lattice Catalysts for Polymer Electrolyte Membrane Fuel Cells: Mathematical Modeling and Experimental Work
This review provides a comprehensive overview on the development of highly active and durable platinum catalysts with ultra-low Pt loadings for polymer electrolyte membrane fuel cells (PEMFCs) through a combined mathematical modeling and experimental work. First, simulation techniques were applied to evaluate the validity of the Tafel approximation for the calculation of the mass activity (MA) and specific activity (SA). A one-dimensional agglomeration model was developed and solved to understand the effects of exchange current density, porosity, agglomerate size, Nafion®film thickness, and Pt loading on the MA and SA. High porosity (> 60%) and agglomerations at high Pt loadings cause the loss of the Tafel approximation and consequently the decrease in MA and SA. A new structure parameter was introduced to estimate the real porous structure using the fractal theory. The volumetric catalyst density was corrected by the fractal dimension (measured by Hg porosimetry), which gave a good agreement with the experimental values. The loading-dependent Tafel equation was then derived, which contains both the utilization and the non-linear scaling factor. Second, activated carbon composite support (ACCS) with optimized surface area, porosity, pore size, and pore size distribution was developed. The hydrophilic/hydrophobic ratio, structural properties (amorphous/crystalline ratio), and the number ofmore »