Power Density Gain Research Articles

Nano-Functionalization of SOFC Electrodes Via Inkjet Printing

Introduction The future of the international accord on mitigating the impact of climate change is linked to the successful commercialisation and implementation of renewable energy technologies. The latter is strongly dependent on finding commercially viable methods for successful dimensional nano-functionalization of the ceramic materials utilized in the fabrication of various energy devices either in energy generation (fuel cells) or storage (batteries, supercapacitors). Inkjet printing digital methods combining scalability and low equipment cost with high-resolution patterning can be a feasible solution for some of the shortcommings of the conventional fabrication technologies. 3D functionalization - Composite solid oxide fuel cells LSCF/CGO cathodes were nano-engineered via “dual” inkjet printing infiltration. The nano-decorated microstructure was found to extend the active three-phase boundary and to promote adsorbtion – dissociation - surface exchange reactions. Composite La0.6Sr0.4Co0.2Fe0.8O3-δ/Ce0.9Gd0.1O1.9 cathodes were subjected to “dual” inkjet printing infiltration of nitrate salt solutions in a single step procedure. After calcination in air at 700 oC the cathodes were decorated with Ce0.9Gd0.1O1.9 and CoxOy nano particles. The effects of as created nano-decoration on the electrochemical activity and the performance stabilty in the intermediate temperature range (500-700 oC) were investigated. The infiltration was found to extend the active three-phase boundary and to promote adsorbtion-dissociation- surface exchange reactions. Electrochemical impedance tests conducted on symmetrical cells showed a reduction in the polarisation resistance of between 1.5 and 7.0 times depending on temperature (500-700 oC). The nano-decoration led to substantially enhanced stability (0.7 Ω•cm2 at 550oC after 100 hours of aging for CGO:CoxOy infiltration). As the composite LSCF/CGO cathodes had already percolating ionic and electronic networks, a low level loading of nanoparticles was sufficient to lead to an efficient short-range extension of the TPB and the density of ORR reaction sites. The sequence of infiltration was shown to influence the efficiency of the ORR promotion. CoxOy:CGO infiltration expanded the available surface area and promoted the catalytical activity towards ORR reaction. The superior effect of CGO:CoxOy infiltration was assigned to the introduction of additional promotion mechanisms (see Fig. 1) resulting in better electrochemical performance at lower temperatures (<650 oC). Both infiltrations suppressed the Sr surface segregation but only CGO:CoxOy infiltrated cathodes showed substantially improved stability after 100 hours of aging. Scaling up - Single step inkjet printing infiltration with doped ceria Ce0.9Ye0.1O1.95 (YDC) and cobalt oxide (CoxOy) precursor inks was performed in order scale-up the modification of the doped ceria interlayer in commercial (50x50x1 mm size) anode supported SOFCs. The penetration of the inks through the mono-phase La0.8Sr0.2Co0.5Fe0.5O3-δ porous cathode to the Gd0.1Ce0.9O2 interlayer was achieved by optimization of inks rheology jetting parameters. The low temperature calcination resulted in densification of the Gd-doped ceria porous interlayer as well as decoration of the cathode scaffold with nano-particles (~ 20-50 nm in size). The I-V testing in pure hydrogen showed maximum power density gain of 20% at 700oC and 97% at 800oC for the infiltrated cells (see Fig. 1). The effect was largely assigned to the improvement in the interfacial Ohmic resistance. The EIS study of the polarization losses of the reference and the infiltrated cells revealed reduction in the activation and concentration polarizations losses at 700oC due to the nano-decoration of the La0.8Sr0.2Co0.5Fe0.5O3-δ scaffold surface. Such effect was not clearly detectable at 800oC where the drop of Ohmic losses was dominant. This work demonstrated that single-step inkjet printing infiltration, a non-disruptive low-cost technique, could produce significant and scalable performance enhancements in commercial SOFCs. Figure 1

Design of a single glass tube optical lens for soft X-ray laser decoherence

Laser has the advantages of high brightness, good monochromaticity, high coherence and good directionality, however, in some cases such as laser imaging and laser processing where only its high brightness or high monochromaticity is desired, the interference effect caused by high coherence can affect and limit its effective applications. In this work, a new single glass tube decoherence lens (SGTDL) is designed for soft X-ray laser decoherence through the simulation calculations. The simulation results show that an SGTDL with an entrance diameter of 5 mm, exit diameter of 0.6 mm and a length of 15 cm can effectively reduce the coherence of the X-ray laser with a wavelength of 10 nm and a beam waist radius of 1.25 mm. At the same time, the exit beam with a divergence range of 30–50 mrad is obtained at the SGTDL’s exit, and the transmission efficiency and gain in power density of the SGTDL are 78% and 52.74, respectively. For a laser beam with a wavelength of up to 1 nm, this model of SGTDL can maintain the transmission efficiency of the beam at more than 30%. This work also discusses the influence of the X-ray laser energy and the SGTDL’s length on the transmission performances of the SGTDL. The results show that the SGTDL designed according to the total reflection principle can meet the application requirements for laser decoherence in a range from the extreme ultraviolet to X-ray wavelength, and has a wide application prospect in X-ray laser imaging, laser processing, etc.

Detailed characterization of polycapillary focusing x-ray lenses by a charge-coupled device detector and a pinhole

A method to measure the detailed performance of polycapillary x-ray optics by a pinhole and charge coupled device (CCD) detector was proposed in this study. The pinhole was located between the x-ray source and the polycapillary x-ray optics to determine the illuminating region of the incident x-ray beam on the input side of the optics. The CCD detector placed downstream of the polycapillary x-ray optics ensured that the incident x-ray beam controlled by the pinhole irradiated a specific region of the input surface of the optics. The intensity of the output beam of the polycapillary x-ray optics was obtained from the far-field image of the output beam of the optics captured by CCD detector. As an application example, the focal spot size, gain in power density, transmission efficiency, and beam divergence of different parts of a polycapillary focusing x-ray lenses (PFXRL) were measured by a pinhole and CCD detector. Three pinholes with diameters of 500, 1000, and 2000 μm were used to adjust the diameter of the incident x-ray beam illuminating the PFXRL from 500 μm to the entire surface of the input side of the PFXRL. The focal spot size of the PFXRL, gain in power density, transmission efficiency, and beam divergence ranged from 27.1 μm to 34.6 μm, 400 to 3460, 26.70% to 5.38%, and 16.8 mrad to 84.86 mrad, respectively.

Inkjet Printing Infiltration of the Doped Ceria Interlayer in Commercial Anode-Supported SOFCs.

Single-step inkjet printing infiltration with doped ceria Ce0.9Ye0.1O1.95 (YDC) and cobalt oxide (CoxOy) precursor inks was performed in order to modify the properties of the doped ceria interlayer in commercial (50 × 50 × 0.5 mm3 size) anode-supported SOFCs. The penetration of the inks throughout the La0.8Sr0.2Co0.5Fe0.5O3−δ porous cathode to the Gd0.1Ce0.9O2 (GDC) interlayer was achieved by optimisation of the inks’ rheology jetting parameters. The low-temperature calcination (750 °C) resulted in densification of the Gd-doped ceria porous interlayer as well as decoration of the cathode scaffold with nanoparticles (~20–50 nm in size). The I–V testing in pure hydrogen showed a maximum power density gain of ~20% at 700 °C and ~97% at 800 °C for the infiltrated cells. The latter effect was largely assigned to the improvement in the interfacial Ohmic resistance due to the densification of the interlayer. The EIS study of the polarisation losses of the reference and infiltrated cells revealed a reduction in the activation polarisations losses at 700 °C due to the nano-decoration of the La0.8Sr0.2Co0.5Fe0.5O3−δ scaffold surface. Such was not the case at 800 °C, where the drop in Ohmic losses was dominant. This work demonstrated that single-step inkjet printing infiltration, a non-disruptive, low-cost technique, can produce significant and scalable performance enhancements in commercial anode-supported SOFCs.

An X-ray focusing monochromator composed of poly-capillary X-ray lenses and highly oriented pyrolytic graphite

An X-ray focusing monochromator is proposed, which is composed of an X-ray source, a highly oriented pyrolytic graphite and two poly-capillary X-ray lenses. Through the function of the front poly-capillary X-ray lens, the X-ray beams diffracted by the highly oriented pyrolytic graphite changed from a linear pattern with high divergence in the vertical direction, to a circular pattern with low divergence, and more X-rays are diffracted than the conventional monochromator of combining an X-ray source with a flat crystal. The post poly-capillary X-ray lens can focus the diffracted X-ray beams with low divergence into a small focal spot with high gain in power density. The results show that the gains of circular apertures with diameters of 320 and 100 μm are 12 and 22, respectively, at a distance of 221.5 mm away from the center of the highly oriented pyrolytic graphite.

Study on the manufacturing process and transmission performance of a nested tapered single capillary X-ray lens

Abstract A new type of tapered single capillary X-ray lens, which is manufactured by using the nesting method, is proposed to generate a small focal spot with high power density gain for micro X-ray analysis. Experimentally, it was found that the nested tapered single capillary has a good geometric shape, and the tubes nest well. The experimental results verify that the nested manufacture process is feasible. Moreover, the transmission performance of the nested tapered single capillary was measured in the laboratory. At a distance 1.5 mm from the exit of the nested tapered single capillary, a beam spot of 9.1 μ m was obtained. The transmission efficiency of the nested tapered single capillary was 55%, and the gain in power density measured with or without the nested tapered single capillary was 16.

Electrodes Modified with Redox Mediators for Improve Charge Transfer in Redox Flow Batteries

Electrochemical performance of iron redox flow batteries (RFBs) was improved through incorporating iron redox mediators into the electrodes. Unpurified carbon nanotubes electrodes containing ferrocene catalysts, from the carbon nanotubes synthesis, are activated to create “hotspots” for Faradaic charge transfer that reduces losses associated with activation, Ohmic, and mass transfer resistances. This permits higher discharge voltages at elevated discharge currents, which from Ohm’s Law (P = iE) establishes augmented power densities. Carbon nanotube electrodes are activated utilizing cyclic voltammetry, in an acidic environment, to initiate charge transfer interactions between redox electrolytes and iron nanoparticles in the electrode. Modified electrodes exhibited 141% gain in power density and a 56.5% improvement in energy density in coin cell devices. Economic value and ready availability of iron paired with enhanced performance makes iron RFBs a viable option for future RFB research. The highest peak power density reported for all-iron RFBs to the author’s awareness was accomplished at 176 mW cm-2 with iron-modified electrodes under no electrolyte flow.

13.1 micrometers hard X-ray focusing by a new type monocapillary X-ray optic designed for common laboratory X-ray source

A new type of monocapillary X-ray optic, called ‘two bounces monocapillary X-ray optics’ (TBMXO), is proposed for generating a small focal spot with high power-density gain for micro X-ray analysis, using a common laboratory X-ray source. TBMXO is consists of two parts: an ellipsoidal part and a tapered part. Before experimental testing, the TBMXO was simulated by the ray tracing method in MATLAB. The simulated results predicted that the proposed TBMXO would produce a smaller focal spot with higher power-density gain than the ellipsoidal monocapillary X-ray optic (EMXO). In the experiment, the TBMXO performance was tested by both an optical device and a Cu target X-ray tube with focal spot of 100 μm. The results indicated that the TBMXO had a slope error of 57.6 μrad and a 13.1 μm focal spot and a 1360 gain in power density were obtained.

Study on durability of Pt supported on graphitized carbon under simulated start-up/shut-down conditions for polymer electrolyte membrane fuel cells

The primary issue for the commercialization of proton exchange membrane fuel cell (PEMFC) is the carbon corrosion of support under start-up/shut-down conditions. In this study, we employ the nanostructured graphitized carbon induced by heat-treatment. The degree of graphitization starts to increase between 900 and 1300 °C as evidenced by the change of specific surface area, interlayer spacing, and ID/IG value. Pt nanoparticles are deposited on fresh carbon black (Pt/CB) and carbon heat-treated at 1700 °C (Pt/HCB17) with similar particle size and distribution. Electrochemical characterization demonstrates that the Pt/HCB17 shows higher activity than the Pt/CB due to the inefficient microporous structure of amorphous carbon for the oxygen reduction reaction. An accelerating potential cycle between 1.0 and 1.5 V for the carbon corrosion is applied to examine durability at a single cell under the practical start-up/shut-down conditions. The Pt/HCB17 catalyst shows remarkable durability after 3000 potential cycles. The Pt/HCB17 catalyst exhibits a peak power density gain of 3%, while the Pt/CB catalyst shows 65% loss of the initial peak power density. As well, electrochemical surface area and mass activity of Pt/HCB17 catalyst are even more stable than those of the Pt/CB catalyst. Consequently, the high degree of graphitization is essential for the durability of fuel cells in practical start-up/shut-down conditions due to enhancing the strong interaction of Pt and π-bonds in graphitized carbon.

A systematic study on the use of short circuiting for the improvement of proton exchange membrane fuel cell performance

Proton exchange membrane fuel cells suffer from reversible performance loss during operation caused by the oxidation of the Pt catalyst which in turn reduces the electrochemically active surface area. Many fuel cell manufacturers recommend using short circuiting during the operation of the fuel cell to improve the performance of the cells over time. However, there is lack of understanding on how it improves the performance as well as on how to optimise the short circuiting strategy for different fuel cell systems. We present a simple procedure to develop an optimised short circuiting strategy by maximising the cumulative average power density gain and minimising the time required to recover the energy loss during short circuiting. We obtained average voltage improvement from 10 to 12% at different current densities for a commercial H-100 system and our short circuiting strategy showed ∼2% voltage improvement in comparison to a commercial strategy. We also demonstrated that the minimum short circuiting time is a function of double layer capacitance by the use of electrochemical impedance spectroscopy.

A self-humidifying acidic–alkaline bipolar membrane fuel cell

To maintain membrane hydration and operate effectively, polymer electrolyte membrane fuel cells (PEMFCs) require elaborate water management, which significantly increases the complexity and cost of the fuel cell system. Here we propose a novel and entirely different approach to membrane hydration by exploiting the concept of bipolar membranes. Bipolar membrane (BPM) fuel cells utilize a composite membrane consisting of an acidic polymer electrolyte membrane on the anode side and an alkaline electrolyte membrane on the cathode side. We present a novel membrane electrode assembly (MEA) fabrication method and demonstrate experimentally and theoretically that BPM fuel cells can (a) self-humidify to ensure high ionic conductivity; and (b) allow use of non-platinum catalysts due to inherently faster oxygen reduction kinetics on an alkaline cathode. Our Pt-based BPM fuel cell achieves a two orders of magnitude gain in power density of 327 mW cm−2 at 323 K under dry gas feed, the highest power output achieved under anhydrous operation conditions. A theoretical analysis and in situ measurements are presented to characterize the unique interfacial water generation and transport behavior that make self-humidification possible during operation. Further optimization of these features and advances in fabricating bipolar MEAs would open the way for a new generation of self-humidifying and water-management-free PEMFCs.

Application of polycapillary x ray lens to eliminate both the effect of x ray source size and scatter of the sample in laboratory tomography

A tomography device based on a conventional laboratory x ray source, polycapillary parallel x ray lens (PPXRL), and polycapillary collimating x ray lens (PCXRL) is designed. The PPXRL can collect the divergent x ray beam from the source and focus it into a quasi-parallel x ray beam with a divergence of 4.7 mrad. In the center of quasi-parallel x ray beam, there is a plateau region with an average gain in power density of 13.8 and a diameter of 630 μm. The contrast of the image can be improved from 28.9% to 56.0% after adding the PCXRL between the sample and the detector.

Potential for wind energy generation in Piracicaba, SP, Brazil

Wind power has gained space in Brazil's energy matrix, being a clean source and inexhaustible. Therefore, it becomes important to characterize the wind potential of a given location, for future applications. The main objective of the present study was to estimate the wind energy potential in Piracicaba, SP, Brazil. The wind speed data were collected by an anemometer installed at the Meteorological Station Luiz de Queiroz College of Agriculture, Piracicaba-SP. The wind speed variability was represented by the Weibull frequency distribution, a probability density function of two parameters (k and c). The parameters k and c were used to correlate the Gamma function with the annual average wind speed, the variance and power mean density. A wind profile was made to evaluate the behavior of historical average speeds at higher altitudes measured by anemometer, to estimate the gain in power density. The values of k for all heights were close to 1 which corresponds to a wind regime highly variable, and c values were also low representing a low average speed of the location. The location was characterized as being unfavorable for the application of wind turbines for power generation.

Performance of polycapillary X-ray optics for confocal energy-dispersive small-angle X-ray scattering

A confocal energy-dispersive small-angle X-ray scattering (EDSAXS) setup based on polycapillary optics was designed. In this confocal EDSAXS setup, a polycapillary slightly focusing X-ray lens (PSFXRL) and a polycapillary parallel X-ray lens (PPXRL) with a long input focal distance were placed confocally in the excitation channel and detection channel, respectively. This confocal configuration was helpful in improving the signal-to-noise ratio of the EDSAXS. The high gain in power density of the PSFXRL and PPXRL decreased the power requirement of the X-ray source for EDSAXS. The confocal EDSAXS technology could be used to perform nondestructive andin situanalysis of samples such as milk powder in its packaging.

Performances for confocal X-ray diffraction technology based on polycapillary slightly focusing X-ray optics

The confocal X-ray diffraction (XRD) technology based on a polycapillary slightly focusing X-ray lens (PSFXRL) in excitation channel and a polycapillary parallel X-ray lens (PPXRL) with a long input focal distance in detection channel was developed. The output focal spot of the PSFXRL and the input focal spot of the PPXRL were adjusted in confocal configuration, and only the X-rays from the volume overlapped by these foci could be accordingly detected. This confocal configuration was helpful in decreasing background. The convergence of the beam focused by the PSFXRL and divergence of the beam which could be collected by the PPXRL with a long input focal distance were both about 9mrad at 8keV. This was helpful in improving the resolution of lattice spacing of this confocal XRD technology. The gain in power density of such PSFXRL and PPXRL was about 120 and 7 at 11keV, respectively, which was helpful in using the low power source to perform XRD analysis efficiently. The performances of this confocal XRD technology were provided, and some common plastics were analyzed. The experimental results demonstrated that the confocal diffraction technology base on polycapillary slightly focusing X-ray optics had wide potential applications.

Simulation of x-ray transmission through an ellipsoidal capillary

This paper develops a simulation program for x-ray transmission in an ellipsoidal capillary based on a ray-tracing method. The influence of the parameters of ellipsoidal capillary and x-ray energy on transmission efficiency, full width at half maximum and power density gain of x-ray beams through an ellipsoidal capillary was analysed by this program. It shows that the particular rules of the ellipsoidal capillary x-ray lens are different from the polycapillary lens. Furthermore, this analysis method can be applied to the optimized design of ellipsoidal capillary.

Focusing synchrotron radiation using a polycapillary half-focusing X-ray lens for imaging

An imaging system based on a polycapillary half-focusing X-ray lens (PHFXRL) and synchrotron radiation source has been designed. The focal spot size and the gain in power density of the PHFXRL were 22 microm (FWHM) and 4648, respectively, at 14.0 keV. The spatial resolution of this new imaging system was better than 5 microm when an X-ray charge coupled device with a pixel size of 10.9 x 10.9 microm was used. A fossil of an ancient biological specimen was imaged using this system.

High Power Density Solid Oxide Fuel Cells for Auxiliary Power Unit Applications

High power density (HPD) solid oxide fuel cells (SOFCs) possess the attributes of reduced ohmic polarization and greater active area per unit volume, relative to current state-of-the-art cylindrical SOFCs. Several variations of the basic “flattened tube” HPD geometry are being analyzed and tested. For example, the HPD10 cell enjoys a 58% gain in power density over current practice. In this variation, ten air channels are separated by nine ribs that connect the flat faces of the cell. Other cell geometries, such as the delta cell, and advanced cell materials are under consideration and have the potential for further improvement in power density. The higher power density makes the application of HPD SOFCs to compact auxiliary power units (APUs) attractive. This paper reviews geometric and performance characteristics for HPD cells and presents a conceptual design for an APU of 5kW net output.

Evaluation of transmitting performance of cylindrical polycapillary

Based on a detailed ray-tracing code for capillary optics, a MATLAB program for the simulation of X-ray transmission in a cylindrical polycapillary is described. The simulated and experimental results for the spatial distributions and power density gain of the X-rays in the beam guided through a cylindrical polycapillary are in good agreement, and the results show that the spatial distribution of the X-rays in the beam guided through a cylindrical polycapillary is uneven.

Higher Power Output in a PEMFC Operating under Autonomous Oscillatory Conditions in the Presence of CO

Time-averaged cell voltage, cell efficiency, and power density in an autonomous oscillatory state was higher than that in stable steady-state for a proton exchange membrane fuel cell ~PEMFC! operating in the presence of CO in the anode feed reformate gas. The average power density under such an oscillatory state at 55°C is twice that under a stable steady state. The average cell voltage and power density gain are due to the decrease of the time-averaged anode overpotential in the oscillatory state. This report thus provides experimental evidence that autonomous oscillatory operation of fuel cells in the presence of CO can increase the power output as compared to that in stable steady-state operation.