Oxygen reduction activity of Pt and Pt-Mn-Co electrocatalysts sputtered on nano-structured thin film support

We report on extensive measurements of oxygen reduction activity of Pt and Pt-Co-Mn electrocatalysts using the rotating ring-disk electrode (RRDE) method. The electrocatalysts were prepared by sputtering from Pt or Pt, Co and Mn targets onto 3M's nano-structured thin film support (NSTF) structures. The area specific activity of Pt/NSTF, measured in 0.1 M HClO₄ and at room temperature, is similar to that of bulk Pt. The area specific measurements show a 20 mV reduction in the Pt-Co-Mn/NSTF overpotential compared to Pt/NSTF. The corresponding kinetic gain in the area specific activity of the ternary alloy is about a factor of two. This ORR enhancement factor observed in the ternary Pt-Co-Mn/NSTF by RRDE measurements is similar to the results obtained in 50 cm² H₂/air fuel cells.     

Estimation of anisotropic properties of nano-structured arrays by modal vibration control at microscale

Nano-structured arrays are engineered to meet the requirements of a variety of applications such as microfilters, sensors, and structural interface due to their unique mechanical characteristics, which cannot be achieved by conventional solid materials. However, it is hard to evaluate the elastic properties of nano-structured arrays owing to the discrete structure, sample size, and availability of suitable techniques. To facilitate this, we develop an advanced three-dimensional microscale vibration testing process. In the test, a specially designed three-dimensional microspecimen with tuned mass is excited by a piezoelectric actuator, and the resonance frequencies are detected by a laser device successfully. The anisotropic elastic moduli of nano-structured array composed of helical nano-springs are identified from a single spectrum. This array shows so strong characteristic anisotropy that the solid one hardly can attain. The microscale testing technique can be extended to other materials and microstructures.     

Performance of large-scale anode-supported solid oxide fuel cells with impregnated La0.6Sr0.4Co0.2Fe0.8O3−δ+Y2O3 stabilized ZrO2 composite cathodes

Anode-supported planar solid oxide fuel cells (SOFCs) with an active area of 81 cm² (9 cm × 9 cm) and nano-structured La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ + Y₂O₃ stabilized ZrO₂ (LSCF + YSZ) composite cathodes are successfully fabricated by tape casting, screen printing, co-firing and solution impregnation, and tested using H₂ fuel and air oxidant at various flow rates. Maximum power densities of 437 and 473 mW cm⁻² are achieved at 750 °C by loading 0.6 and 1.3 mg cm⁻² of LSCF in the composite cathodes, respectively. The gas flow rates, particularly the air, have a significant effect on the cell performance. Cell performance degradation with time is also observed, which is considered to be associated with the growth and coalescence of the nanosized LSCF particles in the composite cathode. The use of the LSCF cathode in combination with YSZ electrolyte without a Gd-doped CeO₂ (GDC) buffer layer is proved to be applicable in large cells, even though the thermal stability of the nanosized LSCF needs to be further improved.     

Electrochemical performance and stability of nano-structured Co/PdO-co-impregnated Y2O3 stabilized ZrO2 cathode for intermediate temperature solid oxide fuel cells

Palladium (Pd) is an attractive cathode catalyst component for solid oxide fuel cells (SOFCs) that has high tendency to agglomerate during operation at around 800 °C. This work shows that such agglomeration can be inhibited by alloying Co into Pd. PdO, Pd_0.95Co_0.05O, Pd_0.90Co_0.10O, and Pd_0.80Co_0.20O were synthesized and characterized. Powder X-ray diffraction patterns at 750 and 900 °C confirmed that PdO decomposition to Pd which normally occurred at 840 °C was suppressed for Co containing Pd alloys while thermal gravimetric analyses indicated improved redox reversibility of PdO ? Pd conversion for alloys during the thermal cycling between 600 and 900 °C. Scanning electron microscopy images supported these arguments. Pd_0.90Co_0.10+yttria stabilized zirconia (YSZ) electrode (i.e., 10 mol % Co containing PdO-impregnated YSZ electrode) displayed the highest oxygen reduction reaction (ORR) performance and stability. The polarization resistance for ORR on Pd_0.90Co_0.10+YSZ cathode is only 0.088 Ω cm² at 750 °C. During polarization test at 750 °C, Pd_0.90Co_0.10+YSZ cathode showed stable performance for 30 h while the performance of Pd+YSZ cathode degraded after 10 h.     

Fabrication and Microstructural Control of Nano-structured Bulk Steels： A Review

There exist strong interests of developing nano-grained steels because of the outstanding properties including high strength/weight ratio, wear resistance, excellent toughness, and favorable cellular activity. This article reviews the main fabrication process and microstructural control of nano-structured steels over the last decades. Severe plastic deformation is considered as an effective route of obtaining the nano-grained microstructures. The process of cold-rolling and annealing of martensitic steel is a viable method to obtain bulk nano-structured low carbon steel, while the final thickness of the cold-rolling plate is limited. According to the theoretical results of the thermal simulation studies, a novel alloy design combined with the rapid transformation and rolling process is proposed to successfully fabricate nano-grained high strength bulk steel. The refinement mechanisms are expected to be taking advantage of increase in the transformation nucleation sites and inhibiting the grain coarsening. Moreover, corresponding mechanical properties are summarized.     

Performance and stability of nano-structured Pd and Pd0.95M0.05 (M = Mn,Co, Ce,and Gd) infiltrated Y2O3–ZrO2 oxygen electrodes of solid oxide electrolysis cells

Nano-structured Pd infiltrated and Pd_0.95M_0.05 (M = Mn, Co, Ce, and Gd) co-infiltrated Y₂O₃–ZrO₂ (YSZ) electrodes are studied as the oxygen electrodes of solid oxide electrolysis cells (SOECs). The infiltrated Pd-YSZ electrodes show good electrocatalytic activity for the oxygen evolution reaction. For example, the electrode polarization resistance (R_E) for 2.0 mg cm⁻² Pd infiltrated YSZ is 0.36 Ω cm⁻² at 800 °C. R_E is not significantly affected by co-infiltrating Pd with Mn and Co, but is enhanced by co-infiltration of Ce and Gd. The co-infiltration of low concentrations of metals in particular Co, Ce and Gd significantly enhances the microstructure and performance stability of the Pd-YSZ electrodes. The results demonstrate that the addition of dopants to the Pd in the form of either an alloy (Co) or a separate phase (Ce and Gd) is beneficial to enhance the performance and stability of Pd based oxygen electrodes of SOECs.     

Fabrication of nano-sized oxide composite coatings and photo-electric conversion/electron storage characteristics

Titanium dioxide TiO₂ can be used as a photo-anode to give generated electrons to the metal substrate under illumination. The transition metal oxide such as iron oxide Fe₂O₃ can be used to store electrons generated by the photo-electric conversion function of TiO₂ under the illuminated situation while the electrons are discharged from the transition metal oxide to the metal substrate in the dark. In this paper, coatings of nano-sized composite of TiO₂ and Fe₂O₃ were fabricated by the Warm Spray process, in which the feedstock powder is accelerated by a supersonic gas jet with speed above 1.0 km s^- 1 and temperature between 800 and 2500 K, and then impacted onto the target substrate continuously to form coatings. The coatings of TiO₂ and Fe₂O₃ nano-composite fabricated by Warm Spray showed no thermal deterioration such as phase transformation and particle growth of the feedstock during the spray process. The coatings fabricated by the Warm Spray had larger photo-current and the electron charge/discharge capacity than that by a conventional HVOF process. In addition, these characteristics were improved by decreasing the primary particle size of TiO₂ and Fe₂O₃.     

Characterization of Bi2S3 nanorods and nano-structured flowers prepared by a hydrothermal method

Bismuth sulfide nanorods and nano-structured flowers were synthesized by hydrothermal reaction of bismuth nitrate pentahydrate and thiourea solutions, containing 1 and 2 ml of 65% HNO₃, respectively. By using X-ray diffraction (XRD), selected area electron diffraction (SAED), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM), the products were specified as orthorhombic Bi₂S₃ in the shapes of nanorods and flower-like clusters of nanorods, with the growth of nanorods in the [001] direction. A diffraction pattern was also simulated, and was in good accordance with the SAED pattern obtained from the experiment.     

High strength-ductility nano-structured high manganese steel produced by cryogenic asymmetry-rolling

A bulk nanostructured twinning-induced plasticity (TWIP) steel with high ductility and high strength was fabricated by cryogenic asymmetry-rolling (cryo-ASR) and subsequent recovery treatment. It was found that the cryo-ASRed TWIP steels exhibit simultaneous improvements in the ductility, strength and work hardening. Typical microstructures of the cryo-ASR TWIP steel were characterized by shear bands and intensive mechanical nano-sized twins induced by cryogenic deformation. These mechanical nano-scale twins remain thermally stable during the subsequent recovery treatment. It is believed that the ductility enhancement and high work-hardening ability for the cryo-ASR TWIP steels should be mainly attributed to the high-density pre-existing nano-scale twins.     

High performance metal-supported intermediate temperature solid oxide fuel cells fabricated by atmospheric plasma spraying

The LSGM(La_0.8Sr_0.2Ga_0.8Mg_0.2O₃) electrolyte based intermediate temperature solid oxide fuel cells (ITSOFCs) supported by porous nickel substrates with different permeabilities are prepared by plasma spray technology for performance studies. The cell having a porous nickel substrate with a permeability of 3.4 Darcy, an LSCM(La_0.75Sr_0.25Cr_0.5Mn_0.5O₃) interlayer on the nickel substrate, a nano-structured LDC(Ce_0.55La_0.45O₂)/Ni anode functional layer, an LDC interlayer, an LSGM/LSCF(La_0.58Sr_0.4Co_0.2Fe_0.8O₃) cathode interlayer and an LSCF cathode current collector layer shows remarkable electric output power densities such as 1270 mW cm⁻² (800 °C), 978 mW cm⁻² (750 °C) and 702 mW cm⁻² (700 °C) at 0.6 V cell voltage under 335 ml min⁻¹ H₂ and 670 ml min⁻¹ air flow rates. SEM, TEM, EDX, AC impedance, voltage and power data with related analyses are presented here to support this high performance. The durability test of the cell with the best power performance shows a degradation rate of about 3% kh⁻¹ at the test conditions of 400 mA cm⁻² constant current density and 700 °C. Results demonstrate the success of APS technology for fabricating high performance metal-supported and LSGM based ITSOFCs.