Evidence of low velocity layers at the top and bottom of the Mantle Transition Zone (MTZ) below the Uttarakhand Himalaya, India

Abstract The Mantle Transition Zone (MTZ) beneath the Uttarakhand Himalaya has been modelled using Common Conversion Point (CCP) stacking and depth-migration of radial P-receiver functions. In the Uttarakhand Himalaya region, the depths of the 410-km discontinuity (d410) and the 660-km discontinuity (d660) are estimated to be approximately 406 ± 8 km and 659 ± 10 km, respectively. Additionally, the thickness of the mantle transition zone (MTZ) is modelled to be 255 ± 7 km. The average arrival times for d410 and d660 conversions are (44.47 ± 1.33) s and (71.08 ± 1.29) s, respectively, indicating an undisturbed slightly deeper d410 and a deformed noticeably deeper d660 in the area. The model identifies the characteristics of the d410 and d660 mantle discontinuities beneath the Lesser Himalayan region, revealing a thickening of the MTZ towards northeast, which could be due to gradual cooling or thickening of the Indian lithosphere towards its northern limit. We simulate a low-velocity layer (perhaps partially molten) above the d410 discontinuity at depths of 350 to 385 km, indicating the presence of a hydrated MTZ beneath the area. We also interpret a negative phase at d660 as a low-velocity layer between 590 and 640 km depths, which could be attributed to the accumulation of old subducted oceanic materials or increased water content at the bottom of the MTZ. Our results suggest the presence of residues from paleo-subducted lithospheric slabs in and below the mantle transition zone underlying the Uttarakhand Himalayas

Unique selectivity trends of highly permeable PAP[5] water channel membranes

Artificial water channels are a practical alternative to biological water channels for achieving exceptional water permeability and selectivity in a stable and scalable architecture. However, channel-based membrane fabrication faces critical barriers such as: (1) increasing pore density to achieve measurable gains in permeability while maintaining selectivity, and (2) scale-up to practical membrane sizes for applications. Recently, we proposed a technique to prepare channel-based membranes using peptide-appended pillar[5]arene (PAP[5]) artificial water channels, addressing the above challenges. These multi-layered PAP[5] membranes (ML-PAP[5]) showed significantly improved water permeability compared to commercial membranes with similar molecular weight cut-offs. However, due to the distinctive pore structure of water channels and the layer-by-layer architecture of the membrane, the separation behavior is unique and was still not fully understood. In this paper, two unique selectivity trends of ML-PAP[5] membranes are discussed from the perspectives of channel geometry, ion exclusion, and linear molecule transport. © 2018 The Royal Society of Chemistry.11Nsciescopu

A scalable membrane electrode assembly architecture for efficient electrochemical conversion of CO2 to formic acid

Abstract The electrochemical reduction of carbon dioxide to formic acid is a promising pathway to improve CO2 utilization and has potential applications as a hydrogen storage medium. In this work, a zero-gap membrane electrode assembly architecture is developed for the direct electrochemical synthesis of formic acid from carbon dioxide. The key technological advancement is a perforated cation exchange membrane, which, when utilized in a forward bias bipolar membrane configuration, allows formic acid generated at the membrane interface to exit through the anode flow field at concentrations up to 0.25 M. Having no additional interlayer components between the anode and cathode this concept is positioned to leverage currently available materials and stack designs ubiquitous in fuel cell and H2 electrolysis, enabling a more rapid transition to scale and commercialization. The perforated cation exchange membrane configuration can achieve >75% Faradaic efficiency to formic acid at <2 V and 300 mA/cm2 in a 25 cm2 cell. More critically, a 55-hour stability test at 200 mA/cm2 shows stable Faradaic efficiency and cell voltage. Technoeconomic analysis is utilized to illustrate a path towards achieving cost parity with current formic acid production methods

Elucidation of Critical Catalyst Layer Phenomena toward High Production Rates for the Electrochemical Conversion of CO to Ethylene

This work utilizes EIS to elucidate the impact of catalyst–ionomer interactions and cathode hydroxide ion transport resistance (RCL,OH–) on cell voltage and product selectivity for the electrochemical conversion of CO to ethylene. When using the same Cu catalyst and a Nafion ionomer, varying ink dispersion and electrode deposition methods results in a change of 2 orders of magnitude for RCL,OH– and ca. a 25% change in electrode porosity. Decreasing RCL,OH– results in improved ethylene Faradaic efficiency (FE), up to ∼57%, decrease in hydrogen FE, by ∼36%, and reduction in cell voltage by up to 1 V at 700 mA/cm2. Through the optimization of electrode fabrication conditions, we achieve a maximum of 48% ethylene with >90% FE for non-hydrogen products in a 25 cm2 membrane electrode assembly at 700 mA/cm2 and RCL,OH– is translated to other material requirements, such as anode porosity. We find that the best performing electrodes use ink dispersion and deposition techniques that project well into roll-to-roll processes, demonstrating the scalability of the optimized process