CO Abundance Research Articles

Recent Advances in Supported Metal Catalysts and Oxide Catalysts for the Reverse Water-Gas Shift Reaction.

The reverse water-gas shift reaction (RWGSR), a crucial stage in the conversion of abundant CO2 into chemicals or hydrocarbon fuels, has attracted extensive attention as a renewable system to synthesize fuels by non-traditional routes. There have been persistent efforts to synthesize catalysts for industrial applications, with attention given to the catalytic activity, CO selectivity, and thermal stability. In this review, we describe the thermodynamics, kinetics, and atomic-level mechanisms of the RWGSR in relation to efficient RWGSR catalysts consisting of supported catalysts and oxide catalysts. In addition, we rationally classify, summarize, and analyze the effects of physicochemical properties, such as the morphologies, compositions, promoting abilities, and presence of strong metal-support interactions (SMSI), on the catalytic performance and CO selectivity in the RWGSR over supported catalysts. Regarding oxide catalysts (i.e., pure oxides, spinel, solid solution, and perovskite-type oxides), we emphasize the relationships among their surface structure, oxygen storage capacity (OSC), and catalytic performance in the RWGSR. Furthermore, the abilities of perovskite-type oxides to enhance the RWGSR with chemical looping cycles (RWGSR-CL) are systematically illustrated. These systematic introductions shed light on development of catalysts with high performance in RWGSR.

Steady Wind-blown Cavities within Infalling Rotating Envelopes: Application to the Broad Velocity Component in Young Protostars

Abstract Wind-driven outflows are observed around a broad range of accreting objects throughout the universe, ranging from forming low-mass stars to supermassive black holes. We study the interaction between a central isotropic wind and an infalling, rotating envelope, which determines the steady-state cavity shape formed at their interface under the assumption of weak mixing. The shape of the resulting wind-blown cavity is elongated and self-similar, with a physical size determined by the ratio between wind ram pressure and envelope thermal pressure. We compute the growth of a warm turbulent mixing layer between the shocked wind and the deflected envelope, and calculate the resultant broad-line profile, under the assumption of a linear (Couette-type) velocity profile across the layer. We then test our model against the warm broad velocity component observed in CO J = 16–15 by Herschel/HIFI in the protostar Serpens-Main SMM1. Given independent observational constraints on the temperature and density of the dust envelope around SMM1, we find an excellent match to all its observed properties (line profile, momentum, temperature) and to the SMM1 outflow cavity width for a physically reasonable set of parameters: a ratio of wind to infall mass flux of ≃4%, a wind speed of v w ≃ 30 km s−1, an interstellar abundance of CO and H2, and a turbulent entrainment efficiency consistent with laboratory experiments. The inferred ratio of ejection to disk accretion rate, ≃6%–20%, is in agreement with current disk wind theories. Thus, the model provides a new framework to reconcile the modest outflow cavity widths in protostars with large observed flow velocities. Being self-similar, it is applicable over a broader range of astrophysical contexts as well.

On the problem of a variable Mars atmospheric composition in the determination of temperature and density from the adiabatic speed of sound

Acoustic anemometry is one of the most precise ways to determine atmospheric temperature on Earth. The technique has similar promise in the Martian atmosphere. Regardless of the atmosphere, temperature is diagnosed from the measured speed of sound using thermodynamic properties that are specific to the composition of the atmosphere. On Mars, the composition of the atmosphere undergoes large seasonal variations due to the exchange of CO2 with the surface. Using standard Mars atmosphere composition instead of the correct, seasonally variable composition can introduce a temperature error of more than 6%, which translates to over 10 ​K for typical Mars temperatures. When this temperature is combined with errors in the specific gas constant, the errors further propagate into the diagnosis of density when using the Ideal Gas Law. A method that incorporates measurements of pressure and CO2 abundance is demonstrated for eliminating compositional errors in diagnosed temperature and density.

Interfacial Active Sites for CO2 Assisted Selective Cleavage of C–C/C–H Bonds in Ethane

Summary Selective upgrading of underutilized ethane in shale gas with greenhouse gas CO2 can produce syngas via dry reforming (C–C bond scission) or ethylene via oxidative dehydrogenation (C–H bond scission). However, it remains challenging to identify active sites responsible for the selective bond cleavage in ethane due to the complexity of supported catalysts. Herein, the ethane-CO2 reaction over CeO2-supported catalysts was investigated to unravel the functions of distinct interfacial sites by combining kinetic measurements with in situ characterizations and calculations: the Pd/CeOx interface is responsible for supplying reactive oxygen species, electron-deficient oxygen species on Pd surface boosts the non-selective bond scission to produce syngas, electron-enriched oxygen in the FeOx/Pd interface enhances the selective scission of C–H bond to yield ethylene, and the FeOx/CeO2 interaction mediates oxygen supply and confines metal ensembles. The current work identifies opportunities for using different interfacial structures in upgrading abundant shale gas and CO2.

CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing

Abstract The gas-phase CO abundance (relative to hydrogen) in protoplanetary disks decreases by up to two orders of magnitude from its interstellar medium value of ∼10−4, even after accounting for freeze-out and photodissociation. Previous studies have shown that while local chemical processing of CO and the sequestration of CO ice on solids in the midplane can both contribute, neither of these processes appears capable of consistently reaching the observed depletion factors on the relevant timescale of 1–3 Myr. In this study, we model these processes simultaneously by including a compact chemical network (centered on carbon and oxygen) to 2D (r + z) simulations of the outer (r > 20 au) disk regions that include turbulent diffusion, pebble formation, and pebble dynamics. In general, we find that the CO/H2 abundance is a complex function of time and location. Focusing on CO in the warm molecular layer, we find that only the most complete model (with chemistry and pebble evolution included) can reach depletion factors consistent with observations. In the absence of pressure traps, highly efficient planetesimal formation, or high cosmic-ray ionization rates, this model also predicts a resurgence of CO vapor interior to the CO ice-line. We show the impact of physical and chemical processes on the elemental (C/O) and (C/H) ratios (in the gas and ice phases), discuss the use of CO as a disk mass tracer, and, finally, connect our predicted pebble ice compositions to those of pristine planetesimals as found in the Cold Classical Kuiper Belt and debris disks.

Influence of the convective mixing-length parameter α on the chemical abundances in the case of metal-poor giant HD 122563

One-dimensional (1D) model atmospheres are still the most commonly used tool for the determination of stellar chemical composition. Convection in the model is usually treated by mixing-length theory (MLT). The mixing-length parameter α is generally calibrated from the Sun and applied to all other stars. The metal-poor giant, HD 122563, is an important benchmark star to test stellar atmosphere and interior physics. We investigate the influence of the convection mixing-length parameter α on the determination of chemical abundances of Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Sr, Y, Zr and Ba in the case of HD 122563, taking advantage of a high resolution and high signal-to-noise ratio HARPS spectrum. The abundance discrepancies Δ[X/H] that occur due to α variation rarely exceed 0.05 dex and most are less than 0.03 dex. We calculate the discrepancy Δ[X/H] using a line-by-line differential analysis. The abundance discrepancies do not have direct relation with either line strength or the excitation potential. For 1D stellar atmospheric analysis of HD 122563, the accuracy of abundance determination does not strongly depend on the choice of mixing-length parameter α (causing average discrepancies of < 0.03 dex), while the uncertainties in the effective temperature and surface gravity play a more important role.

Australian PyroCb Smoke Generates Synoptic‐Scale Stratospheric Anticyclones

AbstractFires in southeastern Australia produced at least 18 pyrocumulonimbus (pyroCb) between 29 December 2019 and 4 January 2020. The largest plumes from this event exhibited several previously undocumented phenomena in the stratosphere. These include (i) the generation of potential vorticity and anticyclonic circulations from absorptive aerosol heating, (ii) the formation of a vertical temperature anomaly dipole, (iii) the rapid ascent from the lowermost stratosphere (15–16 km) to altitudes above 31 km in less than 2 months, (iv) an unprecedented abundance of H2O and CO in the stratosphere, and (v) the displacement of background O3 and N2O from rapid ascent of air from the troposphere and lower stratosphere. Each of these phenomena is traced back to a 5‐day‐old stratospheric plume composed of a massive amount of aerosol and biomass burning gases from a pyroCb outbreak. Until now, there has been no documented evidence that pyroCb plumes can affect stratospheric winds.

Carbon monoxide conversion and syngas biomethanation mediated by different microbial consortia

Syngas biomethanation is an attractive process for extending application of gasification products. In the present study, anaerobic sludges from three methanogenic reactors feeding cattle manure (CS), sewage sludge (SS) and gaseous H2/CO2 (GS) were used to investigate the effect of microbial consortia composition on syngas biomethanation. The results showed that CS presented the highest CO consumption rate due to its highest relative abundance of CO consuming bacteria. The CO was mainly converted to acetate, and syntrophic acetate oxidization (SAO) bacteria converted acetate to H2/CO2 for hydrogenotrophic methanogenesis in CS and SS. However, acetate was accumulated in GS for lacking acetoclastic methanogens and SAO bacteria, leading to lower biomethanation efficiency. Additionally, adding stoichiometric H2 could convert CO and CO2 to nearly pure methane, while, the CO consumption rate declined in H2 added systems. The results present novel insights into microbial consortia on CO conversion and syngas biomethanation.

Information Content of JWST NIRSpec Transmission Spectra of Warm Neptunes

Abstract Warm Neptunes offer a rich opportunity for understanding exo-atmospheric chemistry. With the upcoming James Webb Space Telescope (JWST), there is a need to elucidate the balance between investments in telescope time versus scientific yield. We use the supervised machine-learning method of the random forest to perform an information content (IC) analysis on a 11-parameter model of transmission spectra from the various NIRSpec modes. The three bluest medium-resolution NIRSpec modes (0.7–1.27 μm, 0.97–1.84 μm, 1.66–3.07 μm) are insensitive to the presence of CO. The reddest medium-resolution mode (2.87–5.10 μm) is sensitive to all of the molecules assumed in our model: CO, CO2, CH4, C2H2, H2O, HCN, and NH3. It competes effectively with the three bluest modes on the information encoded on cloud abundance and particle size. It is also competitive with the low-resolution prism mode (0.6–5.3 μm) on the inference of every parameter except for the temperature and ammonia abundance. We recommend astronomers to use the reddest medium-resolution NIRSpec mode for studying the atmospheric chemistry of 800–1200 K warm Neptunes; its corresponding high-resolution counterpart offers diminishing returns. We compare our findings to previous JWST IC analyses that favor the blue orders and suggest that the reliance on chemical equilibrium could lead to biased outcomes if this assumption does not apply. A simple, pressure-independent diagnostic for identifying chemical disequilibrium is proposed based on measuring the abundances of H2O, CO, and CO2.

Temporal variation of the halide ions (F−, Cl−, Br−, I−) in medium-temperature (46–52 °C) thermal waters from the Sob-1 and Sob-2 wells, the Mura Basin, north-eastern Slovenia

An eleven-year monitoring (1987/88–1999) of chemical composition of Na-HCO3 thermal water from the wells Sob-1 and Sob-2 has shown long- and short-time scale changes occurring as a result of mixed character of abstracted thermal water and overexploitation of the wells. Constantly reoccurring changes of dynamic pressure induced the inflow of variable proportions of water from the most productive aquifer Thermal I and from lower-permeability aquifers in the underlying Lendava Formation which contain abundant CO2. The chloride ions originate from formation waters in the Lendava Formation, and for Thermal I, a local natural background is 80–85 mg/L. The fluoride ions mainly originate from waters in the Lendava Formation but do not correlate entirely with the chloride ions. It is assumed their abundance is largely controlled by interaction of CO2-rich waters with detritial marine carbonates and clay minerals. Temporal variations of concentrations of the bromide and iodide ions in thermal water from the Sob-1 largely correlate with variation of the chloride ions and indicate that the Lendava Formation is their major source. By overexploitation, some low-permeability aquifers in the Lendava Formation have been activated along with leakage from clayey lenses rich in organic matter and coal in the Mura Formation. The sources rich in the bromide and iodide, and iodide and chloride ions have been also recognized in the Sob-2 well at high pumping rate that amounted to 8.7 L/sec.

Roles of fault structures on the distribution of mantle-derived CO2 in the Bohai Bay basin, NE China

Based on studies on the contents, origin and filling history of CO2, and the seismic interpretation of the Bohai Sea, the sea area of the Bohai Bay basin, the distribution of mantle-derived CO2 and roles of fault structures have been examined in this study. Mantle-derived CO2 is mainly distributed in the structures within the Bozhong area, the center of the Bohai Sea. Laser Raman spectrum shows that CO2 inclusions are symbiotic with hydrocarbon inclusions with a charging time no earlier than 5.1 Ma. Late-stage (5.1–0 Ma) active basement faults are the major pathways for the migration of mantle-derived CO2. The intensity of the activity influences the CO2 content. Abundant CO2 occurs in the structures with basement faults that have relatively high fault activity rate (FAR) values. Along the basement fault, high CO2 content appears near the segments with high FAR values. Fault combination patterns affect the accumulation layers of mantle-derived CO2. Structures with fault combination patterns that resemble a “flower” or “Y” commonly accumulate CO2 in Cenozoic shallow layers as well. The branch faults that intersect with basement faults facilitate the adjustment of CO2 from deep to shallow layers. The uplifted mantle is the deep tectonic context, and the upwelling mantle magma is the source of the development of mantle-derived CO2. Below the middle crust, mantle-derived CO2 may be vertically transported along the lithosphere-scale strike–slip faults. Within the middle and upper crust, the late-stage active basement faults are the major conduits for mantle-derived CO2.

Recent Advances in the Photoautotrophic Metabolism of Cyanobacteria: Biotechnological Implications.

Cyanobacteria constitute the only phylum of oxygen-evolving photosynthetic prokaryotes that shaped the oxygenic atmosphere of our planet. Over time, cyanobacteria have evolved as a widely diverse group of organisms that have colonized most aquatic and soil ecosystems of our planet and constitute a large proportion of the biomass that sustains the biosphere. Cyanobacteria synthesize a vast array of biologically active metabolites that are of great interest for human health and industry, and several model cyanobacteria can be genetically manipulated. Hence, cyanobacteria are regarded as promising microbial factories for the production of chemicals from highly abundant natural resources, e.g., solar energy, CO2, minerals, and waters, eventually coupled to wastewater treatment to save costs. In this review, we summarize new important discoveries on the plasticity of the photoautotrophic metabolism of cyanobacteria, emphasizing the coordinated partitioning of carbon and nitrogen towards growth or compound storage, and the importance of these processes for biotechnological perspectives. We also emphasize the importance of redox regulation (including glutathionylation) on these processes, a subject which has often been overlooked.

Determination of optimum CO2 water alternating gas (CO2-WAG) ratio in Sumatera Light Oilfield

The CO2 Water Alternating Gas (CO2-WAG) injection method, allows the oil to first expand and become better able to flow because of the CO2, and then the water increases the pressure in the reservoir to flush this newly freed oil to production wells. This study is in Sarolangun District, Jambi Province which is prospect of CO2 injection tertiary recovery project due to its abundant CO2 reserve. The success of CO2-WAG injection can be determined by investigating ratios between CO2 and water. The goal of this study is to determine optimum CO2-WAG injection ratio in Sumatera Light Oilfield. This study is done through a numerical simulation of immiscible CO2-WAG which is conducted under three scenarios of ratio using both CMG WINPROP and GEM simulator. The CO2/water ratios are varied from 1:1, 2:1 and 1:2. The study results show that the CO2/water 1:2 is the best CO2-WAG injection ratio that gives highest additional oil recovery factor of 35.24%. Additional recovery factor given by CO2/water ratio 2:1 and 1:1 is 1.49% and 19.52% respectively. Based on this study, the effect of CO2-WAG ratio to oil productivity is depending of amount of water injected. Lower initial oil viscosity lead to an insignificant effect of CO2. Proper CO2-WAG injection ratio will give an optimum oil recovery. This works will have a great use in the CO2-Enhanced Oil Recovery (EOR) application.

Comparing the quality characteristics and bacterial communities in meatballs with or without blown pack spoilage

Differences of the quality characteristics and bacterial communities in meat products with or without blown pack spoilage (BPS) were not well illustrated. The objectives of this study were to investigate the quality characteristics and bacteria of meatballs with or without BPS, to explain the possible cause of meat products with BPS. The results revealed a 12.5% BPS ratio with meatballs and the pack volumes in the BPS samples were nearly two-fold larger than those of the normal samples after storage for 28 days. Compared with the normal group, the meatballs in the BPS group had a higher CO2 abundance (78.53%) and a lower pH (5.09). Besides, the relative concentrations of some spoilage-related compounds (such as acetic acid) were significantly higher in BPS meatballs (P < 0.05). Principal component analysis provided evidence of clear differences in the bacterial communities between the BPS and normal groups. Pseudomonas (30.46%), Enterobacter (20.76%), Pantoea (13.38%), Serratia (12.63%), and Rahnella (10.15%) were dominant in the BPS group, whereas Pseudomonas (42.51%), Carnobacterium (18.74%), Pantoea (17.56%), and Enterobacter (14.80%) were dominant in the normal group. The findings of this study may provide a theoretical basis for understanding potential mechanisms underlying BPS.

Survey of Molecular Emission Lines in the WB 673 Interstellar Filament

We report observations of molecular line emission toward dense clumps of the WB 673 interstellar filament: WB 668, WB 673, S233–IR, and G173.57+2.43. The observations were done with the 20-m telescope at the Onsala Space Observatory (Sweden). Maps of emission, column densities, and relative abundances of CO, N2H $$^{ + }$$ , CS, HCN, and HNC molecules are presented. It was found that the molecular abundances decrease toward the peaks of molecular hydrogen column densities in the clumps.

Sensitivity of gas-grain chemical models to surface reaction barriers

Context. The feasibility of contemporary gas-grain astrochemical models depends on the availability of accurate kinetics data, in particular, for surface processes. Aims. We study the sensitivity of gas-grain chemical models to the energy barrier Ea of the important surface reaction between some of the most abundant species: C and H2 (surface C + surface H2 → surface CH2). Methods. We used the gas-grain code ALCHEMIC to model the time-dependent chemical evolution over a 2D grid of densities (nH ∈ 103, 1012 cm−3) and temperatures (T ∈ 10, 300 K), assuming UV-dark (AV = 20 mag) and partly UV-irradiated (AV = 3 mag) conditions that are typical of the dense interstellar medium. We considered two values for the energy barrier of the surface reaction, Ea = 2500 K (as originally implemented in the networks) and Ea = 0 K (as measured in the laboratory and computed by quantum chemistry simulations). Results. We find that if the C + H2 → CH2 surface reaction is barrierless, a more rapid conversion of the surface carbon atoms into methane ice occurs. Overproduction of the CHn hydrocarbon ices affects the surface formation of more complex hydrocarbons, cyanides and nitriles, and CS-bearing species at low temperatures ≲10−15 K. The surface hydrogenation of CO and hence the synthesis of complex (organic) molecules become affected as well. As a result, important species whose abundances may change by more than a factor of two at 1 Myr include atomic carbon, small mono-carbonic (C1) and di-carbonic (C2) hydrocarbons, CO2, CN, HCN, HNC, HNCO, CS, H2CO, H2CS, CH2CO, and CH3OH (in either gas and/or ice). The abundances of key species, CO, H2O, and N2 as well as O, HCO+, N2H+, NH3, NO, and most of the S-bearing molecules, remain almost unaffected. Conclusions. Further accurate laboratory measurements and quantum chemical calculations of the surface reaction barriers will be crucial to improve the accuracy of astrochemical models.

2D Electrocatalysts: 2D Electrocatalysts for Converting Earth‐Abundant Simple Molecules into Value‐Added Commodity Chemicals: Recent Progress and Perspectives (Adv. Mater. 18/2020)

The renewable electricity-driven electrocatalytic conversion of abundant N2, O2, CO2, CH4, H2O, and NaCl into value-added commodity chemicals will bring a new paradigm of electrocatalysis that transforms the current chemical production regime with enormous socioeconomic and environmental benefits. In article number 1904870, Porun Liu, Huijun Zhao, and co-workers review advances in 2D electrocatalysts for such emerging applications.

N-Doped Nanoporous Carbon Scaffold As an Electrocatalyst for CO2 Reduction

The rising level of CO2 in the atmosphere poses a major threat to our global climate [1]. Renewable energy are promising alternatives but the utilization of renewable energy is challenging because of its intermittency. The key solution is to develop an energy storage system that can store energy and then release it as needed. CO2 reduction reaction (CO2RR) uses abundant CO2 present in the atmosphere and renewable energy as the input power. Therefore, increasing interest has been focused on electrochemical routes to transform CO2 into useful products. However, the reduction of CO2 is thermodynamically and kinetically unfavorable. To overcome the energy barrier of CO2RR, the development of high efficiency and high selectivity catalysts is a key goal of CO2RR research.Metallic catalysts have attracted much attention for CO2RR and have achieved some successes. However, most metallic catalysts exhibit large CO2RR overpotentials and insufficient selectivity. Also, the high price of noble metals is a key obstacle to scale-up and commercialization of these materials for CO2RR.Carbon is a very promising candidate to advance CO2RR due to its high specific surface areas and good conductivity. However, carbon atoms are electrically neutral and therefore it is difficult to activate the CO2 molecules and adsorb the intermediate. Therefore, it is necessary to develop novel carbon catalysts to enhance their catalytic activity for CO2RR. Nitrogen is the most commonly used carbon doping atom due to its high electronegativity, which leads to polarization of the adjacent carbon atoms, thus enhancing the electronic/ionic conductivity [2]. Many carbon materials, such as carbon nanotubes and graphene, have been doped with N and investigated as CO2RR catalysts [3][4], with some N-doped materials exhibiting a 85% Faradaic efficiency towards CO production[5].In this work, a nitrogen-doped templated nanoporous carbon scaffold (N-doped NCS) was investigated as a catalyst material for electrochemical CO2 reduction. The NCS is a novel, templated, binder-free, self-supported, fully tunable mesoporous carbon material[6] that gives a high active site density and good conductivity.NCS material, having a pore size of either 12, 50 or 85 nm, was heated in NH3 gas at 700 °C for 7 hours to prepare N-doped NCS. SEM and TEM were used to confirm the NCS morphology, while XPS, EDX and elemental analysis were used to determine the N content of the NCS material. The electrochemical performance of the N-doped NCS was carried out first using CV in CO2 sat. 0.1 M KHCO3 in a glass cell. After that, a membrane electrode assembly (MEA) CO2 electrolyzer was used to determine the CO2 reduction activity. An N-doped NCS (IrO2-coated) was used as the anode and an anion exchange membrane (AEM) was used as the separator during CO2 electrolysis, with humidified CO2 gas used at the cathode side. The gas products were collected from the cathode outlet and injected into a gas chromatography system for analysis. No liquid products were observed in the solution that was released to the cell outlet.The performance of N-doped NCS will be presented based on the results obtained in various solution-flow cell configurations. Effect of N-doped NCS preparation optimization will also be discussed. Based on both the CV results and the MEA CO2 electrolyzer data, the onset potential of CO2RR was comparable to what has been reported by others for N-doped carbons, but the high internal surface area of the NCS, combined with its high extent of N doping, may give the N-doped NCS some advantages. A maximum 90% FECO was achieved and the stability of the catalytic material was also studied in the flow cell systems.

Advance Electrochemical CO2 Utilization Towards Higher Industrial Readiness: Across Multiple Scales from Catalyst Design, Electrode Decoration, to Reactor Engineering

The challenges in electro-catalytic mitigation of CO2 press innovations across multiple scales going from catalyst structure at microscale to the complex multiphase thermofluids network at system scale. In this presentation, I will demonstrate a molecular electrocatalyst active for CO2 to methanol conversion, a pioneering catalyst restructuring technique to realize 12-day CO2-formate inter-conversion, a polymer-molecular catalyst hybrid gas diffusion electrode to reduce CO2 in presence of O2 just like the industrial flue gases, an alkaline based micro-flow reactor to boost the CO2 electro-reduction performance, and an unprecedented in-situ platform to reveal the near-electrode local environment in a flow reactor. At microscale: catalyst design. An integration combining the functions of a CO2 electrolyzer and a formate fuel cell is a new option for carbon‐neutral energy storage but entails rapid, reversible and stable interconversion between CO2 and formate over a single catalyst. We develop a new catalyst with such functionalities based on a Pb–Pd alloy system that reversibly restructures its phase, composition, and morphology and thus alters its catalytic properties under controlled electrochemical conditions. Under cathodic conditions, the catalyst is relatively Pb‐rich and is active for CO2‐to‐formate conversion over a wide potential range; under anodic conditions, it becomes relatively Pd‐rich and gains stable catalytic activity for formate‐to‐CO2 conversion. The bifunctional activity and superior durability of our Pb–Pd catalyst leads to the first proof‐of‐concept demonstration of an electrochemical cell that can switch between the CO2 electrolyzer/formate fuel cell modes and can stably operate for 12 days. At mesoscale: electrode design. The electrochemical reduction of CO2 in the presence of O2 would allow the direct valorization of flue gases from fossil fuel combustion and of CO2 captured from air. However, it is a challenging task because O2 reduction is thermodynamically favored over that of CO2. Typically, 5% O2 in the CO2 feed gas is sufficient to completely inhibit the CO2 reduction reaction. We developed an O2-tolerant catalytic CO2 reduction electrode inspired by part of the natural photosynthesis unit. The electrode comprises of heterogenized cobalt phthalocyanine molecules serving as the cathode catalyst with > 95% Faradaic efficiency (FE) for CO2 reduction to CO coated with a polymer of intrinsic microporosity that works as a CO2-selective layer with a CO2/O2 selectivity of ~ 20. Integrated into a flow electrolytic cell, the hybrid electrode operating with a CO2 feed gas containing 5% O2 exhibits a FECO of 75.9% with a total current density of 27.3 mA/cm2 at a cell voltage of 3.1 V. A FECO of 49.7% can be retained when the O2 fraction increases to 20%. Stable operation for 18 h is achieved. The electrochemical performance and O2 tolerance can be further enhanced by introducing cyano and nitro substituents to the phthalocyanine ligand. At macro scale: reactor system design and probing the cathode surface environment. The promise and challenge of electrochemical mitigation of CO2 calls for innovations on both catalyst and reactor levels. Enabled by high-performance and earth abundant CO2 electroreduction catalyst materials, we developed alkaline microflow electrolytic cells for energy-efficient, selective, fast, and durable CO2 conversion to CO and formate. With the above-mentioned cobalt phthalocyanine-based cathode catalyst, the CO-selective cell starts to operate at a 0.26 V overpotential and reaches a Faradaic efficiency of 94% and a partial current density of 31 mA/cm2 at a 0.56 V overpotential. With a SnO2-based cathode catalyst, the formate-selective cell starts to operate at a 0.76 V overpotential and reaches a Faradaic efficiency of 82% and a partial current density of 113 mA/cm2 at a 1.36 V overpotential. In contrast to previous studies, it was found that the overpotential reduction from using the alkaline electrolyte is mostly contributed by a pH gradient near the cathode surface, which was validated by direct observations in a Raman-enhanced novel in-situ platform.

Bimetallic ZnCo zeolitic imidazolate framework/polypyrrole-polyaniline derived Co/N-doped carbon for oxygen reduction reaction

Non-noble-metal based materials with high activity for oxygen reduction reaction (ORR) are urgently required to substitute Pt-based materials. Herein, metallic Co/N-doped carbon electrocatalysts were synthesized via a facile pyrolysis method of bimetal ZIF(ZnCo)/polypyrrole-polyaniline (ppy-pani) precursors. The evaporation of Zn and the introduced ppy-pani can lead to the porous structure and effectively hinder the aggregation of Co species, which results in the small nanoparticles uniformly distributed on carbon matrices. A high ECSA and a high content of Co species are obtained after the introduction of ppy-pani, thus resulting in the abundant Co2+ species to enhance ORR. Therefore, the optimized ZIF/ppy-pani-750 exhibits a high E1/2 (~0.86 V) and a low Tafel slope (~43.6 mV dec−1).