Materials for Energy Infrastructure

Nanostructured, responsive hydrogels composed of oppositely charged triblock copolymers with charged end-blocks and neutral, hydrophilic mid-blocks in aqueous solution were recently discovered. Due to electrostatic interactions, the end-blocks microphase separate and form physical cross-links that are bridged by the mid-blocks. Since these hydrogels are hydrophilic and have the ability to respond to a variety of stimuli including temperature and salt concentration, they are promising for a variety of biomedical applications including, but not limited to, drug delivery and tissue scaffolds. For such applications, there is a need to understand how to control the structure of the hydrogel. To this end, we use a new, efficient model along with self-consistent field theory to determine the structure as a function of polymer concentration and end-block fraction. After identifying numerous phases including a sphere phase, a hexagonally packed cylinder phase, a lamellar phase, and regions of phase coexistence, we determine how the polymer functionality can be tuned to manipulate the resulting phase diagram.

Undoped and doped ceria were synthesized by a solid state reaction and a polymerized—complex method. Microstructural and phase development of M_xCe_1-xO_2-δ (M = Zr, Hf; 0 ≤ x ≤ 0.2) were examined using X-ray diffraction and scanning electron microscopy. Redox properties were investigated by thermogravimetric analysis and a remarkable increase of the oxygen storage capacity of ceria with increasing dopant concentration was demonstrated. Zr_xCe_1-xO₂ and Hf_xCe_1-xO₂ solid solutions at x = 0.2 were shown to release double the amount of oxygen during reduction compared to undoped ceria. The solid state reaction synthesis produces materials with excellent redox performance up to 15 mol% dopant concentration and is otherwise equivalent with materials produced by Pechini synthesis.

Duplex stainless steels have been used for a long time in the offshore industry, since they have higher strength than conventional austenitic stainless steels and they exhibit a better ductility as well as an improved corrosion resistance in harsh environments compared to ferritic stainless steels. However, despite these good properties the literature shows some failure cases of duplex stainless steels in which hydrogen plays a crucial role for the cause of the damage. Numerical simulations can give a significant contribution in clarifying the damage mechanisms. Therefore, a numerical model of a duplex stainless steel microstructure was developed enabling simulation of crack initiation and propagation in both phases. The phase specific stress strain analysis revealed that local plastic deformation occurs in both austenite and δ-ferrite already in the macroscopically elastic range. Altogether, phase specific hydrogen-assisted material damage was simulated for the first time taking into account all main factors influencing hydrogen assisted cracking process. The results agree well with experimental observations and thus allow a better insight in the mechanism of hydrogen-assisted material damage.

Effect of the grain size and sample size were examined with different grain size below 20 nm and sample size from 30 to 5 μm fabricated from electroplated nickel. TEM observation confirmed smallest grain size of 8 nm obtained at applied pressure of 15 MPa. On the contrary to the Hall–Petch relationship reported before, inverse Hall–Petch was not observed in our nanocrystalline nickel even when the grain size at 8 nm. Sample size effect on the 8 nm grained nickel was smaller than that of single crystal nickel as Hall–Petch exponent of −0.25 and −0.125 respectively. Suppressed Hall–Petch breakdown and sample size effect were explained by the physics of grain boundaries in association with impurity carbon.

Using first-principles electronic structure methods in conjunction with nonequilibrium Green function (NEGF) techniques, we study the thermoelectric transport through biphenyl-based single-molecule junctions. We show, based on our recently published works and their present extension to include also the electron energy current, that the single-molecule conductance, junction thermopower, and electron thermal conductance strongly depend on the choice of the molecular anchor group and on the geometry of the investigated gold-biphenyl-gold contacts. We compare two different anchor groups, sulfur and cyano. The electron-donating S anchor group gives rise to a positive thermopower, while the electron-withdrawing cyano anchor results in a negative thermopower. For the S-terminated biphenyl a strong variation of the transport coefficients with respect to the binding motif is observed, for CN-terminated biphenyl such variations remain small.

The refinement of Fe-intermetallic compounds in aluminum alloys has been extensively studied by various processes in order to improve the properties of high Fe-containing recycled aluminum. In this study, the Deformation Semi-Solid Forming (D-SSF) process was applied to modify the coarse intermetallic compounds into more favorable particles by thermo-mechanical deformation and subsequently heating to the semi-solid state. The evolution of the fragmented Fe-intermetallic compounds of the Al–Mg–Si–Fe alloy was investigated during heating to various semi-solid temperatures by the D-SSF process. The fragmented Fe-intermetallic compound was transformed into the polyhedral shape in the initial stage and subsequently spheroidized shape at the low semi-solid temperatures between 580–610 °C. The phase transformation of β-Al₅FeSi to α-Al₈Fe₂Si was found during the evolution of the morphologies. At temperatures higher than 613 °C, fragmented Fe-intermetallic compounds gradually completely melt into the liquid phase with long holding time. The Fe-intermetallic compounds are stable as solid phase at low semi-solid temperature. Therefore, the semi-solid forming should be performed at low semi-solid temperatures in order to preserve the fine fragmented Fe compounds from coarsening and melting.

As a chemical metrology tool time-of-flight secondary ion mass spectrometry (ToF-SIMS) has become a very popular technique to monitor the elemental, isotopic and molecular distribution in two or three dimensions. Its reduced sampling depth, high sensitivity, great structural specificity and the direct detection of hydrogen thereby increase the emergence of ToF-SIMS for material and analytical surface science, particularly due to recent instrumental developments improving mass, depth and lateral resolution. For basic surface science, adsorption processes and surface reactivity thus can be investigated in high detail on organic as well as inorganic samples. The use of multivariate data analysis in addition can effectively assist to identify trends in the complex SIMS raw data set and define key co-variances between certain samples or mass spectra. In this contribution the essence of ToF-SIMS is illustrated by discussing two highly relevant energy applications. First, for piezoelectric electroceramics oxygen exchange active zones have been visualized to determine the impact of external field-load to the oxygen vacancy distribution between anode and cathode. As a second case study the interaction of hydrogen species with the microstructure of a duplex stainless steel was investigated. It was concluded that ToF-SIMS has a valuable essence for detailing hydrogen related degradation mechanisms.

Organic semiconductors can be deposited or printed from solution and thus offer the possibility of low cost, high throughput, roll-to-roll manufacture of electronic devices on flexible substrates. To date organic semiconductors have been used to make transistors, light emitting diodes (OLEDs), photovoltaics (OPVs) and more. With the aim of low cost generation of renewable energy, a large part of the research into OPV materials has focused on increasing the power conversion efficiency of devices, reducing the production cost and enhancing lifetime such that they are competitive in a marketplace with other photovoltaic technologies. Indeed, environmental stability has become a major barrier to large scale applications and recently growing effort has been dedicated to this matter. In this work we present a study of the degradation of OPV devices using a novel device chamber in which the O₂ and H₂O content of the atmosphere can be highly controlled. We measure the performance over time of OPV devices in an inert atmosphere, as well as in atmospheres with various levels of oxygen. Unexpected changes in device performance are observed upon exposure to oxygen, such as an increase in the open circuit voltage. Crucially, the measurements also allow determination of the threshold oxygen level below which no change in device performance is observed.

the bifunctional catalyst is one of the crucial components of rechargeable metal-air batteries, which should have good stability and high catalytic activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) during the discharging and charging processes, respectively. Herein, high-performance, non-precious metal-based hybrid bifunctional catalysts are developed from post-synthesis integration of spinel MnCo₂O₄ nanocrystals with nanocarbon materials. The hybrid catalysts exhibited comparable ORR activity and superior OER activity as compared to a commercial 30 wt.% Pt on carbon black (Pt/C). Rechargeable zinc-air batteries using these spinel-nanocarbon hybrid catalysts on cathode was successfully operated for 64 discharge-charge cycles (or 768 h equivalent), which significantly out-performed the Pt/C counterpart that could only survive up to 108 h under similar test conditions.

A Monte Carlo simulation is used to investigate the structure of binary alloys in bulk and nanostructured systems. The structures simulated under the bulk constraint by prohibiting grain boundary states to appear are in good agreement with microstructures in conventional alloy phase diagrams. Structures obtained without forcing the bulk constraint are found to differ from the bulk configurations and display nanoscale structural features that are accessible with suitable nanostructuring and equilibration. A nanostructure stability map is shown to be a useful tool for determining the alloy structures that may emerge from the Monte Carlo simulation without the bulk constraint.

The knowledge of the dynamics of intrinsic point defects, is essential for controlling and engineering their formation and clustering and thus also the quality of the germanium crystals used for producing germanium wafers for space solar cells and terrestrial concentrator photovoltaic, as well as of the active layer of germanium in complementary metal-oxide semiconductors technology. The analyses presented in this paper relate technological process parameters with microdefect formation in single crystal germanium.

The engineer’s methods use different approaches to calculate fire and smoke spread in enclosures and compartments. The method of Computational Fluid dynamics CFD is being increasingly used for this. For risk assessment safety parameters like temperature development in the compartment, smoke layer height or radiant heat from the fire can be predicted with CFD. This investigation focused on the prediction of critical concentrations and visibility of fire smoke. The challenge was to find a suitable method to investigate and access the effects of smoke, toxic smoke products and heat experimentally and numerically. At first a large set of experimental investigations were performed to analyze toxic and optical properties of fire smoke on different temperature and ventilation conditions. Therefore three different polymers were investigated under thermal decomposition in the DIN-tube furnace and under flaming combustion conditions in the Cone Calorimeter. The particular interest was on how the amount of the fire effluents changes under different temperature and ventilation conditions and consequently how the smoke toxicity changes. From the experimental investigations complex combustion formulas were set up to account for different combustion conditions in the simulation. For the evaluation of smoke toxicity or the exposure to toxic products for occupants the concept of Fractional Effective Dose (FED) was used. The next step was to develop a numerical model to simulate fire smoke, calculate the smoke toxicity and visibility. The numerical simulations were done with the fluid dynamics programm ANSYS CFX. This program is used to simulate fluid flow in a variety of application. CFX has to be modified for application in fire safety engineering. According to this the concept of the Fractional Effective Dose and the calculated reaction equations were implemented in ANSYS CFX. Another aspect was to investigate the change of visibility under different combustion conditions and to predict the visibility numerically. This work is part of a Ministry-funded project that aims the development of an advanced numerical approach to model smoke production, smoke distribution and toxicity using several CFD codes.