Electrochemical CO₂ Reduction to CO Catalyzed by 2D Nanostructures

Electrochemical CO₂ reduction towards value-added chemical feedstocks has been extensively studied in recent years to resolve the energy and environmental problems. The practical application of electrochemical CO₂ reduction technology requires a cost-effective, highly efficient, and robust catalyst. To date, vigorous research have been carried out to increase the proficiency of electrocatalysts. In recent years, two-dimensional (2D) graphene and transition metal chalcogenides (TMCs) have displayed excellent activity towards CO₂ reduction. This review focuses on the recent progress of 2D graphene and TMCs for selective electrochemical CO₂ reduction into CO

Master singular behavior from correlation length measurements for seven one-component fluids near their gas-liquid critical point

We present the master (i.e. unique) behavior of the correlation length, as a function of the thermal field along the critical isochore, asymptotically close to the gas-liquid critical point of xenon, krypton, argon, helium 3, sulfur hexafluoride, carbon dioxide and heavy water. It is remarkable that this unicity extends to the correction-to-scaling terms. The critical parameter set which contains all the needed information to reveal the master behavior, is composed of four thermodynamic coordinates of the critical point and one adjustable parameter which accounts for quantum effects in the helium 3 case. We use a scale dilatation method applied to the relevant physical variables of the onecomponent fluid subclass, in analogy with the basic hypothesis of the renormalization theory. This master behavior for the correlation length satisfies hyperscaling. We finally estimate the thermal field extent, where the critical crossover of the singular thermodynamic and correlation functions deviate from the theoretical crossover function obtained from field theory.Comment: Submitted to Physical Review

Electrochemical CO₂ Reduction to CO Catalyzed by 2D Nanostructures

Electrochemical CO₂ reduction towards value-added chemical feedstocks has been extensively studied in recent years to resolve the energy and environmental problems. The practical application of electrochemical CO₂ reduction technology requires a cost-effective, highly efficient, and robust catalyst. To date, vigorous research have been carried out to increase the proficiency of electrocatalysts. In recent years, two-dimensional (2D) graphene and transition metal chalcogenides (TMCs) have displayed excellent activity towards CO₂ reduction. This review focuses on the recent progress of 2D graphene and TMCs for selective electrochemical CO₂ reduction into CO

Advanced Palladium Membrane Scale-up for Hydrogen Separation

The main objective of this project was to construct, test, and demonstrate a Pd-Cu metallic tubular membrane micro-channel separator capable of producing 2 lb day{sup -1} H{sub 2} at â¥95% recovery when operating downstream of an actual coal gasifier. A key milestone for the project was to complete a pilot-scale gasifier test by 1 September 2011 and demonstrate the separation of 2 lb day{sup -1} H{sub 2} to verify progress toward the DOEâs goals prior to down-selection for larger-scale (â100 lb day{sup -1}) hydrogen separator development. Three different pilot-scale (â1.5 ft{sup 2}) separators were evaluated downstream of coal gasifiers during four different tests and the key project milestone was achieved in August 2011, ahead of schedule. During three of those tests, all of the separators demonstrated or exceeded the targeted separation rate of 2 lb day{sup -1} H{sub 2}. The separator design was proved to be leak tight and durable in the presence of gasifier exhaust contaminants at temperatures and pressures up to 500 °C and 500 psia. The contaminants in the coal gasifier syngas for the most part had negligible impact on separator performance, with H{sub 2} partial pressure being the greatest determinant of membrane performance. Carbon monoxide and low levels of H{sub 2}S (100 ppmv) were shown to significantly reduce H{sub 2} separation performance. The presence of trace metals, including mercury and arsenic, appeared to have no effect based on the experimental data. Subscale Pd-Cu coupon tests further quantified the impact of H{sub 2}S on irreversible sulfide formation in the UTRC separators. Conditions that have a thermodynamic driving force to form coke were found to reduce the performance of the separators, presumably by blockage of effective separation area with carbon deposits. However, it was demonstrated that both in situ and ex situ (laboratory) air regeneration at 450 °C could restore separator performance by burning out such deposits. Gasifier testing revealed that high molecular weight hydrocarbons have the potential to retard H2 separation. Unconverted coal tars with carbon numbers greater than 14 have a boiling point such that they can act as a reversible poison to the Pd-Cu membranes even at temperatures above 500 °C. The use of real-time, physics-based, performance models revealed the effect of these coal tars. It is believed that this project provided the first evidence for the impact of coal tars on H{sub 2} separator performance. Final down-selection of candidate alloys for non-membrane materials of construction proceeded by evaluating the alloys in both UTRC laboratory tests and testing downstream of an actual gasifier at the National Carbon Capture Center (NCCC). The overall alloy ratings were calculated by multiplying the projected cost of a 100 lb day{sup -1} H{sub 2} separator outer shell by the projected oxide scale thickness for 5 years of operation. The alloy with the lowest resulting rating parameter was stainless steel 309 (SS-309) followed by stainless steel 310 (SS-310). However, it was noted that approximately half of the alloys showed susceptibility to pitting and localized corrosion. SS-309 was one of the alloys that exhibited heavy localized attack after 2000 hours of laboratory testing. As this localized corrosion can potentially lead to accelerated end of life, it was determined that SS-310 would be the best alloy selection for this application as it does not show signs of localized pitting corrosion

Master crossover functions for the one-component fluid "subclass"

Introducing three well-defined dimensionless numbers, we establish the link between the scale dilatation method able to estimate master (i.e. unique) singular behaviors of the one-component fluid "subclass" and the universal crossover functions recently estimated [Garrabos and Bervillier, Phys. Rev. E 74, 021113 (2006)] from the bounded results of the massive renormalization scheme applied to the..

Electrochemical CO2 Reduction to CO Catalyzed by 2D Nanostructures

Electrochemical CO2 reduction towards value-added chemical feedstocks has been extensively studied in recent years to resolve the energy and environmental problems. The practical application of electrochemical CO2 reduction technology requires a cost-effective, highly efficient, and robust catalyst. To date, vigorous research have been carried out to increase the proficiency of electrocatalysts. In recent years, two-dimensional (2D) graphene and transition metal chalcogenides (TMCs) have displayed excellent activity towards CO2 reduction. This review focuses on the recent progress of 2D graphene and TMCs for selective electrochemical CO2 reduction into CO. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.1

Experimental Demonstration of Advanced Palladium Membrane Separators for Central High Purity Hydrogen Production

The overall objectives for this project were to: (1) confirm the high stability and resistance of a PdCu trimetallic alloy to carbon and carbide formation and, in addition, resistance to sulfur, halides, and ammonia; (2) develop a sulfur, halide, and ammonia resistant alloy membrane with a projected hydrogen permeance of 25 m{sup 3}m{sup -2}atm{sup -0.5}h{sup -1} at 400 C and capable of operating at pressures of 12.1 MPa ({approx}120 atm, 1750 psia); and (3) construct and experimentally validate the performance of 0.1 kg/day H{sup 2} PdCu trimetallic alloy membrane separators at feed pressures of 2 MPa (290 psia) in the presence of H{sub 2}S, NH{sub 3}, and HCl. This project successfully increased the technology readiness level of palladium-based metallic membranes for hydrogen separation from coal-biomass gasifier exhaust or similar hydrogen-containing gas streams. The reversible tolerance of palladium-copper (PdCu) alloys was demonstrated for H{sub 2}S concentrations varying from 20 ppmv up to 487 ppmv and NH{sub 3} concentrations up to 9 ppmv. In addition, atomistic modeling validated the resistance of PdCu alloys to carbon formation, irreversible sulfur corrosion, and chlorine attack. The experimental program highlighted two key issues which must be addressed as part of future experimental programs: (1) tube defects and (2) non-membrane materials of construction. Four out of five FCC PdCu separators developed leaks during the course of the experimental program because {approx}10% of the alloy tubes contained a single defect that resulted in a thin, weak point in the tube walls. These defects limited operation of the existing tubes to less than 220 psig. For commercial applications of a PdCu alloy hydrogen separator under high sulfur concentrations, it was determined that stainless steel 316 is not suitable for housing or supporting the device. Testing with sulfur concentrations of 487 {+-} 4 ppmv resulted in severe corrosion of the stainless steel components of the separators. The project identified an experimental methodology for quantifying the impact of gas contaminants on PdCu alloy membrane performance as well as an atomistic modeling approach to screen metal alloys for their resistance to irreversible sulfur corrosion. Initial mathematical descriptions of the effect of species such as CO and H{sub 2}S were developed, but require further experimental work to refine. At the end of the project, an improvement to the experimental approach for acquiring the necessary data for the permeability model was demonstrated in preliminary tests on an enhanced PdCu separator. All of the key DOE 2010 technical targets were met or exceeded except for the hydrogen flux. The highest flux observed for the project, 125 ft{sup 3}ft{sup -2}h{sup -1}, was obtained on a single tube separator with the aforementioned enhanced PdCu separator with a hydrogen feed pressure of 185 psig at 500 C

Master singular behavior for the Sugden factor of the one-component fluids near their gas-liquid critical point

We present the master (i.e. unique) behavior of the squared capillary length - so called the Sudgen factor-, as a function of the temperature-like field along the critical isochore, asymptotically close to the gas-liquid critical point of twenty (one component) fluids. This master behavior is obtained using the scale dilatation of the relevant physical fields of the one-component fluids. The scale dilatation introduces the fluid-dependent scale factors in a manner analog with the linear relations between physical fields and scaling fields needed by the renormalization theory applied to the Ising-like universality class. The master behavior for the Sudgen factor satisfies hyperscaling and can be asymptotically fitted by the leading terms of the theoretical crossover functions for the correlation length and the susceptibility in the homogeneous domain recently obtained from massive renormalization in field theory. In the absence of corresponding estimation of the theoretical crossover functions for the interfacial tension, we define the range of the temperature-like field where the master leading power law can be practically used to predict the singular behavior of the Sudgen factor in conformity with the theoretical description provided by the massive renormalization scheme within the extended asymptotic domain of the one-component fluid "subclass"

Preparation and characterization of superhydrophobic surfaces based on hexamethyldisilazane-modified nanoporous alumina

Superhydrophobic nanoporous anodic aluminum oxide (alumina) surfaces were prepared using treatment with vapor-phase hexamethyldisilazane (HMDS). Nanoporous alumina substrates were first made using a two-step anodization process. Subsequently, a repeated modification procedure was employed for efficient incorporation of the terminal methyl groups of HMDS to the alumina surface. Morphology of the surfaces was characterized by scanning electron microscopy, showing hexagonally ordered circular nanopores with approximately 250 nm in diameter and 300 nm of interpore distances. Fourier transform infrared spectroscopy-attenuated total reflectance analysis showed the presence of chemically bound methyl groups on the HMDS-modified nanoporous alumina surfaces. Wetting properties of these surfaces were characterized by measurements of the water contact angle which was found to reach 153.2 ± 2°. The contact angle values on HMDS-modified nanoporous alumina surfaces were found to be significantly larger than the average water contact angle of 82.9 ± 3° on smooth thin film alumina surfaces that underwent the same HMDS modification steps. The difference between the two cases was explained by the Cassie-Baxter theory of rough surface wetting