Carbon utilization is a crucially important performance characteristic of CO2 electrolyzers; however, applications of simple and accurate descriptive models to experimental data on this topic are ...currently lacking. Here, we apply a simple analytical reactor model to parameterize single-pass conversion as a function of feed-gas flow rate and show that it captures a wide body of experimental data in the literature exceptionally well. In doing so, we demonstrate that this simple conceptual approach can characterize progress and capture recent innovations in reactor design. To validate the extracted parameters, we employ a well-established comprehensive model to confirm that the results agree with physical expectations. Lastly, we explore the implications of the descriptive model by examining the inherent trade-off between single-pass conversion efficiency and reactor productivity. Understanding such trade-offs is crucially important for advancing this electrolyzer technology toward commercial applications.
Pulsed electrolysis has been demonstrated to improve the faradaic efficiency (FE) to C2+ products during the electrochemical reduction of CO2 over a Cu catalyst, but the nature of this enhancement is ...poorly understood. Herein, we developed a time-dependent continuum model of pulsed CO2 electrolysis on Cu in 0.1 M CsHCO3 that faithfully represents the experimentally observed effects of pulsed electrolysis. This work shows that pulsing results in dynamic changes in the pH and CO2 concentration near the Cu surface, which lead to an enhanced C2+ FE as a consequence of repeatedly accessing a transient state of heightened pH and CO2 concentration at high cathodic overpotential. Using these insights, a variety of pulse shapes were explored to establish operating conditions that maximize the rate of C2+ product formation and minimize the rates of H2 and C1 product formation.
Seismic traveltime tomography involves finding a velocity model that minimizes the error energy between the measured and the theoretical traveltimes. When solving this nonlinear inverse problem, a ...local optimization technique can easily produce a solution for which the gradient of the error energy function vanishes, but the energy function itself does not take its global minimum. Other methods such as simulated annealing can be applied to such global optimization problems. The simulated annealing approach to seismic traveltime tomography described in this paper has been tested on synthetic as well as real seismic data. It is shown that unlike local methods, the convergence of the simulated annealing algorithm is independent of the initial model: even in cases of virtually no prior information, it is capable of producing reliable results. The method can provide a number of acceptable solutions. When prior information is sparse, the solution of the global optimization can be used as an input to a local optimization procedure, such as, e.g., simultaneous iterative reconstruction technique (SIRT), producing an even more accurate result.
We describe the characteristics of single-crystal GaN regions obtained by selective-area and subsequent lateral epitaxial overgrowth using metalorganic chemical vapor deposition. For a range of ...deposition conditions, the surface kinetics of the metalorganic chemical vapor deposition process results in an initial stage of selective-area growth, subsequently followed by the lateral growth of single-crystal GaN over the SiO
2 mask. The lateral-to-vertical relative growth rate depends upon the orientation of stripe openings with respect to the GaN crystal planes, the ratio of the “open” stripe width to the “masked” stripe width, and the specific growth conditions (e.g., temperature and V/III ratio). The crystalline orientations of the growth facets on the sidewalls of the laterally growing stripes are also dependent upon the growth conditions. The results of cathodoluminescence and transmission-electron microscopy studies of the GaN films indicate that materials with improved quality are grown over the oxide mask.
Transparent conducting ZnO contacts to GaN, of light transmittance >70% in the visible spectrum have been prepared by thermal oxidation of vacuum deposited zinc. For low‐doped p‐GaN the contact ...exhibits ohmic behaviour (1 × 10–2 Ω cm2); on low‐doped n‐GaN a Schottky barrier (0.56 eV) is observed. We find the properties of ZnO contact promising for optoelectronic device applications.
Over the past few decades, a significant amount of research on polymer-electrolyte fuel cells (PEFCs) has been conducted to improve performance and durability while reducing the cost of fuel cell ...systems. However, the cost associated with the platinum (Pt) catalyst remains a barrier to their commercialization and PEFC durability standards have yet to be established. An effective path toward reducing PEFC cost is making the catalyst layers (CLs) thinner thus reducing expensive Pt content. The limit of thin CLs is high gas-transport resistance and the performance of these CLs is sensitive to the operating temperature due to their inherent low water uptake capacity, which results in higher sensitivity to liquid-water flooding and reduced durability. Therefore, reducing PEFC's cost by decreasing Pt content and improving PEFC's performance and durability by managing liquid-water are still challenging and open topics of research. An overlooked aspect nowadays of PEFC water management is the gas-diffusion layer (GDL). While it is known that GDL's properties can impact performance, typically it is not seen as a critical component. In this work, we present data showing the importance of GDLs in terms of water removal and management while also exploring the interactions between liquid-water and GDL surfaces. The critical interface of GDL and gas-flow-channel in the presence of liquid-water was examined through systematic studies of adhesion forces as a function of water-injection rate for various GDLs of varying thickness. GDL properties (breakthrough pressure and adhesion force) were measured experimentally under a host of test conditions. Specifically, the effects of GDL hydrophobic (PTFE) content, thickness, and water-injection rate were examined to identify trends that may be beneficial to the design of liquid-water management strategies and next-generation GDL materials for PEFCs.
PDF
