The electrolysis of CO 2 to syngas (CO + H 2 ) using nonprecious metal electrocatalysts was studied in bipolar membrane-based electrochemical cells. Electrolysis was carried out using aqueous bicarbonate and humidified gaseous CO 2 on the cathode side of the cell, with Ag or Bi/ionic liquid cathode electrocatalysts. In both cases, stable currents were observed over a period of hours with an aqueous alkaline electrolyte and NiFeO x electrocatalyst on the anode side of the cell. In contrast, the performance of the cells degraded rapidly when conventional anionand cation-exchange membranes were used in place of the bipolar membrane. In agreement with earlier reports, the Faradaic efficiency for CO 2 reduction to CO was high at low overpotential. In the liquid-phase bipolar membrane cell, the Faradaic efficiency was stable at about 50% at 30 mA/cm 2 current density. In the gas-phase cell, current densities up to 200 mA/cm 2 could be obtained, albeit at lower Faradaic efficiency for CO production. At low overpotentials in the gas-phase cathode cell, the Faradaic efficiency for CO production was initially high but dropped within 1 h, most likely because of dewetting of the ionic liquid from the Bi catalyst surface. The effective management of protons in bipolar membrane cells enables stable operation and the possibility of practical CO 2 electrolysis at high current densities.
The ability to precisely maneuver micro/nano objects in fluids in a contactless, biocompatible manner can enable innovative technologies and may have far-reaching impact in fields such as biology, chemical engineering, and nanotechnology. Here, we report a design for acoustically powered bubble-based microswimmers that are capable of autonomous motion in three dimensions and selectively transporting individual synthetic colloids and mammalian cells in a crowded group without labeling, surface modification, or effect on nearby objects. In contrast to previously reported microswimmers, their motion does not require operation at acoustic pressure nodes, enabling propulsion at low power and far from an ultrasonic transducer. In a megahertz acoustic field, the microswimmers are subject to two predominant forces: the secondary Bjerknes force and a locally generated acoustic streaming propulsive force. The combination of these two forces enables the microswimmers to independently swim on three dimensional boundaries or in free space under magnetical steering.
SUMMARY Common fragile sites (CFSs) are genomic regions that are unstable under conditions of replicative stress. Although the characteristics of CFSs that render them vulnerable to stress are mainly associated with replication, the cellular pathways that protect CFSs during replication remain unclear. Here, we identify and describe a role for FANCD2 as a trans-acting facilitator of CFS replication, in the absence of exogenous replicative stress. In the absence of FANCD2, replication forks stall within the AT-rich fragility core of CFS leading to dormant origin activation. Furthermore, FANCD2 deficiency is associated with DNA:RNA hybrid formation at CFS-FRA16D and inhibition of DNA:RNA hybrid formation suppresses replication perturbation. In addition, we also found that FANCD2 reduces the number of potential sites of replication initiation. Our data demonstrate that FANCD2 protein is required to ensure efficient CFS replication and provide mechanistic insight into how FANCD2 regulates CFS stability.
Hydrogen energy-based electrochemical energy conversion technologies offer the promise of enabling a transition of the global energy landscape from fossil fuels to renewable energy. Here, we present a comprehensive review of the fundamentals of electrocatalysis in alkaline media and applications in alkaline-based energy technologies, particularly alkaline fuel cells and water electrolyzers. Anion exchange (alkaline) membrane fuel cells (AEMFCs) enable the use of nonprecious electrocatalysts for the sluggish oxygen reduction reaction (ORR), relative to proton exchange membrane fuel cells (PEMFCs), which require Pt-based electrocatalysts. However, the hydrogen oxidation reaction (HOR) kinetics is significantly slower in alkaline media than in acidic media. Understanding these phenomena requires applying theoretical and experimental methods to unravel molecularlevel thermodynamics and kinetics of hydrogen and oxygen electrocatalysis and, particularly, the proton-coupled electron transfer (PCET) process that takes place in a proton-deficient alkaline media. Extensive electrochemical and spectroscopic studies, on single-crystal Pt and metal oxides, have contributed to the development of activity descriptors, as well as the identification of the nature of active sites, and the rate-determining steps of the HOR and ORR. Among these, the structure and reactivity of interfacial water serve as key potential and pH-dependent kinetic factors that are helping elucidate the origins of the HOR and ORR activity differences in acids and bases. Additionally, deliberately modulating and controlling catalyst−support interactions have provided valuable insights for enhancing catalyst accessibility and durability during operation. The design and synthesis of highly conductive and durable alkaline membranes/ionomers have enabled AEMFCs to reach initial performance metrics equal to or higher than those of PEMFCs. We emphasize the importance of using membrane electrode assemblies (MEAs) to integrate the often separately pursued/optimized electrocatalyst/support and membranes/ionomer components. Operando/in situ methods, at multiscales, and ab initio simulations provide a mechanistic understanding of electron, ion, and mass transport at catalyst/ionomer/membrane interfaces and the necessary guidance to achieve fuel cell operation in air over thousands of hours. We hope that this Review will serve as a roadmap for advancing the scientific understanding of the fundamental factors governing electrochemical energy conversion in alkaline media with the ultimate goal of achieving ultralow Pt or precious-metal-free highperformance and durable alkaline fuel cells and related technologies.
Bipolar membranes maintain a steady pH in electrolytic cells through water autodissociation at the interface between their cation- and anion-exchange layers. We analyze the balance of electric field and catalysis in accelerating this reaction.
that combine an anode reaction, typically oxygen evolution, with the CO 2 RR for the conversion of CO 2 to organic products has been gaining attention as well.  In order to be economically competitive, CO 2 electrolysis devices must achieve operating parameters that are similar to those of commercial water electrolyzers. That is, they should be able to operate continuously with high Faradaic and energy efficiency, and with current densities in the 1-2 A cm −2 range. At such high current densities, product crossover needs to be considered as a loss mechanism. In fuel cell technology, particularly in direct alcohol fuel cells, organic molecules can pass through polymer electrolyte membranes (PEMs) to be oxidized electrocatalytically, substantially lowering the overall efficiency of the device.  Because crossover is primarily driven by electrokinetic effects, its rate increases with increasing current density. For CO 2 electrolysis, even though there is no universal device design as yet, product crossover issues should be anticipated and indeed have already been identified in some studies of PEM-based CO 2 electrolyzers.  Thus, there is a need to identify membranes that can meet the operating requirements of CO 2 electrolysis cells while minimizing product crossover.Several groups have recently demonstrated the benefits of using bipolar membranes (BPMs) to maintain a steady electrolyte pH and prevent electrolyte crossover in electrolysis cells. With monopolar membranes, these performance parameters can be achieved only at extremes of pH.  Over the past few years, BPMs have been successfully incorporated into both electrochemical and photo-electrochemical devices for water and CO 2 electrolysis. [3c,7] In a BPM, anion-and cation-exchange layers are joined together at an interfacial layer that catalyzes the autodissociation of water. Under reverse bias conditions, H + and OH − ions are generated in the catalytic layer and are driven outward. The flux of protons in the BPM opposes the direction of product crossover from the cathode to the anode of an electrolytic cell. Thus, one should expect the electromigration of anionic products, as well as transport of neutral molecules by electroosmotic drag, to be minimized in BPM-based CO 2 electrolysis cells.We compare here crossover through anion-exchange membranes (AEMs) and BPMs in cells that simulate the conditions As electrocatalysts and electrolyzer designs for CO 2 reduction continue to improve in terms of current density and product selectivity, product crossover from the cathode to the anode is a loss mechanism that is relatively unexplored. The crossover rates of formate, methanol, and ethanol, which are desirable CO 2 reduction products, are compared in electrolyzers containing anion-exchange membranes and bipolar membranes. The crossover of formate, an anionic CO 2 reduction product, occurs by electromigration through anion-exchange membranes, and its rate increases linearly with current density. Crossover of electroneutral methanol or ethanol thr...
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