Proton exchange membrane electrolysis sustained by water vapor

The current–voltage characteristics of a proton exchange membrane (PEM) electrolyzer constructed with an IrRuOx water oxidation catalyst and a Pt black water reduction catalyst, under operation with water vapor from a humidified carrier gas, have been investigated as a function of the gas flow rate, the relative humidity, and the presence of oxygen. The performance of the system with water vapor was also compared to the performance when the device was immersed in liquid water. With a humidified Ar(g) input stream at 20 °C, an electrolysis current density of 10 mA cm^(−2) was sustained at an applied voltage of ~ 1.6 V, with a current density of 20 mA cm^(−2) observed at ~ 1.7 V. In the system evaluated, at current densities >40 mA cm^(−2) the electrolysis of water vapor was limited by the mass flux of water to the PEM. At <40 mA cm^(−2), the electrolysis of water vapor supported a given current density at a lower applied bias than did the electrolysis of liquid water. The relative humidity of the input carrier gas strongly affected the current–voltage behavior, with lower electrolysis current density attributed to dehydration of the PEM at reduced humidity values. The results provide a proof-of-concept that, with sufficiently active catalysts, an efficient solar photoelectrolyzer could be operated only with water vapor as the feedstock, even at the low operating temperatures that may result in the absence of active heating. This approach therefore offers a route to avoid the light attenuation and mass transport limitations that are associated with bubble formation in these systems

Mexican Immigrant Parents\u27 Beliefs and Practices Related to Literacy

The purpose of this study was to describe the literacy practices and beliefs exhibited by immigrant parents of Mexican descent in Oregon. The researcher collected data using a questionnaire and examined the correlation between generational differences of immigrants and respondents\u27 beliefs and practices regarding reading and writing. From the survey sample, the researcher selected 5 representative families for observations and interviews to further explore how literacy is practiced in Mexican immigrant families\u27 homes and daily lives. The belief regarding whether or not children begin learning before they go to school generated the most disagreement amongst participants. Data correlating acculturation and literacy practices resulted in a Pearson r of .494, a moderate correlation statistically significant at the p \u3c .01 level

Diffusion bonding and its application to manufacturing

In its simplest form diffusion bonding is accomplished by placing clean metal surfaces together under a sufficient load and heating. The natural interatomic attractive force between atoms transforms the interface into a natural grain boundary. Therefore, in principle, the properties of the bond area are identical to those of the parent metal. Other advantages of diffusion bonding over conventional methods of bonding include freedom from residual stresses, excessive deformation, foreign metals, or changed crystal structures. Stainless steels, nickel-base superalloys, and aluminum alloys have all been successfully joined. Complex hardware, including integrated flueric devices, jet engine servovalves, and porous woven structures have been fabricated. The processing involved is discussed, along with such theoretical considerations as the role of metal surfaces, the formation of metal contact junctions, and the mechanisms of material transport in diffusion bonding

Design of an Unknown Input Observer to Enhance Driver Experience of Electric Power Steering Systems

Electric power steering (EPS) systems assist the driver during manoeuvres by applying an additional steering torque generated by an electric motor. Although there are many advantages for electric actuated steering systems including fuel efficiency, they are known to deteriorate the feel of the steering as experienced by the driver. This paper presents a sliding mode observer based estimation concept which provides signals to evaluate and improve perception and feel of the steering as experienced by the driver. The proposed strategy is based on a physically motivated dynamic model of a power steering system and the measurements considered are typically available in any modern vehicle. The performance of the estimator is investigated using numerical simulation as well as experimental results obtained using a laboratory steering testbed

A Robust Exact Differentiator Toolbox for Matlab®/Simulink®

This paper demonstrates the functionality and ease of use of a recently implemented robust exact differentiator block for numerical simulations performed within the Matlab/Simulink software environment. It is demonstrated that the differentiator block may be used for various applications and may be easily integrated within existing Simulink models. The underpinning discrete-time differentiation algorithm is briefly outlined and its parameters for differentiator orders up to 10 are presented. An extended version of the toolbox supports the so-called automatic code generation feature of Matlab/Simulink. This functionality allows compilable code to be produced for many available hardware platforms. Three applications are presented in the paper, two of which require the generation of executable code. The third simulation-based application presents a differentiator based edge detection algorithm for image processing purposes which directly utilises the Simulink block. The three applications employ differentiators of order 4, 3 and 2, respectively

Repeated epitaxial growth and transfer of arrays of patterned, vertically aligned, crystalline Si wires from a single Si(111) substrate

Multiple arrays of Si wires were sequentially grown and transferred into a flexible polymer film from a single Si(111) wafer. After growth from a patterned, oxide-coated substrate, the wires were embedded in a polymer and then mechanically separated from the substrate, preserving the array structure in the film. The wire stubs that remained were selectively etched from the Si(111) surface to regenerate the patterned substrate. Then the growth catalyst was electrodeposited into the holes in the patterned oxide. Cycling through this set of steps allowed regrowth and polymer film transfer of several wire arrays from a single Si wafer

Adaptive sliding mode dynamic positioning control for a semi-submersible offshore platform

In this paper, an adaptive sliding mode dynamic positioning control approach is proposed for a semi-submersible offshore platform. The actuator dynamics are slow and thus a first order sliding mode control approach is used to maximise tracking accuracy in the presence of typically unmodelled actuator dynamics. The sliding mode control is designed with an adaptive feedback gain to counter the effects of model uncertainty and external disturbances such as the waves. The control implementation uses a sliding mode differentiator for online estimation of velocity and acceleration. The stability of the system is analyzed using Lyapunov methods. The control algorithm is validated using illustrative examples

Silicon and tungsten oxide nanostructures for water splitting

Inorganic semiconductors are promising materials for driving photoelectrochemical water-splitting reactions. However, there is not a single semiconductor material that can sustain the unassisted splitting of water into H_2 and O_2. Instead, we are developing a three part cell design where individual catalysts for water reduction and oxidation will be attached to the ends of a membrane. The job of splitting water is therefore divided into separate reduction and oxidation reactions, and each catalyst can be optimized independently for a single reaction. Silicon might be suitable to drive the water reduction. Inexpensive highly ordered Si wire arrays were grown on a single crystal wafer and transferred into a transparent, flexible polymer matrix. In this array, light would be absorbed along the longer axial dimension while the resulting electrons or holes would be collected along the much shorter radial dimension in a massively parallel array resembling carpet fibers on a microscale, hence the term "solar carpet". Tungsten oxide is a good candidate to drive the water oxidation. Self-organized porous tungsten oxide was successfully synthesized on the tungsten foil by anodization. This sponge-like structure absorbs light efficiently due to its high surface area; hence we called it "solar sponge"