Study of pyridine-mediated electrochemical reduction of CO2 to methanol at high CO2 pressure

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The recently proposed highly efficient route of pyridine-catalyzed CO 2 reduction to methanol was explored on platinum electrodes at high CO 2 pressure. At 55 bar (5.5 MPa) of CO 2 , the bulk electrolysis in both potentiostatic and galvanostatic regimes resulted in methanol production with Faradaic yields of up to 10 % for the first 5–10 C cm −2 of charge passed. For longer electrolysis, the methanol concentration failed to increase proportionally and was limited to sub-ppm levels irrespective of biasing conditions and pyridine concentration. This limitation cannot be removed by electrode reactivation and/or pre-electrolysis and appears to be an inherent feature of the reduction process. In agreement with bulk electrolysis findings, the CV analysis supported by simulation indicated that hydrogen evolution is still the dominant electrode reaction in pyridine-containing electrolyte solution, even with an excess CO 2 concentration in the solution. No prominent contribution from either a direct or coupled CO 2 reduction was found. The results obtained suggest that the reduction of CO 2 to methanol is a transient process that is largely decoupled from the electrode charge transfer

“Hot Edges” in Inverse Opal Structure Enable Efficient CO2 Electrochemical Reduction and Sensitive in-situ Raman Characterization

Conversion of CO 2 into fuels and chemicals via electroreduction has attracted significant interest. Via mesostructure design to tune the electric field distribution in the electrode, it is demonstrated that the Cu-In alloy with an inverse opal (CI-1-IO) structure provides efficient electrochemical CO 2 reduction and allows for sensitive detection of the CO 2 reduction intermediates via surface-enhanced Raman scattering. The significant enhancement of Raman signals of the intermediates on the CI-1-IO surface can be attributed to electric field enhancement on the "hot edges" of the inverse opal structure. Additionally, a highest CO 2 reduction faradaic efficiency (FE) of 92% (sum of formate and CO) is achieved at-0.6 V vs. RHE on the CI-1-IO electrode. The diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results show that the Cu-In alloy with an inverse opal structure has faster adsorption kinetics and higher adsorption capacity for CO 2. The "hot edges" of the bowl-like structure concentrate electric fields, due to the high curvature, and also concentrate K + on the active sites, which can lower the energy barrier of the CO 2 reduction reaction. This research provides new insight into the design of materials for efficient CO 2 conversion and the detection of intermediates during the CO 2 reduction process. </p

Production of C-2/C-3 Oxygenates from Planar Copper Nitride-Derived Mesoporous Copper via Electrochemical Reduction of CO2

Electrochemical reduction of CO2 provides an opportunity to produce fuels and chemicals in a carbon-neutral manner, assuming that CO2 can be captured from the atmosphere. To do so requires efficient, selective, and stable catalysts. In this study, we report a highly mesoporous metallic Cu catalyst prepared by electrochemical reduction of thermally nitrided Cu foil. Under aqueous saturated CO2 reduction conditions, the Cu3N-derived Cu electrocatalyst produces virtually no CH4, very little CO, and exhibits a faradaic efficiency of 68% in C2+ products (C2H4, C2H5OH, and C3H7OH) at a current density of ∼18.5 mA cm-2 and a cathode potential of -1.0 V versus the reversible hydrogen electrode. Under these conditions, the catalyst produces more oxygenated products than hydrocarbons. We show that surface roughness is a good descriptor of catalytic performance. The roughest surface reached 98% CO utilization efficiency for C2+ product formation from CO2 reduction and the ratio of oxygenated to hydrocarbon products correlates with the degree of surface roughness. These effects of surface roughness are attributed to the high population of undercoordinated sites as well as a high pH environment within the mesopores and adjacent to the surface of the catalyst

High purity H2 by sorption-enhanced chemical looping reforming of waste cooking oil in a packed bed reactor.

High purity hydrogen (>95%) was produced at 600 degrees C and 1 atm by steam reforming of waste cooking oil at a molar steam to carbon ratio of 4 using chemical looping, a process that features redox cycles of a Ni catalyst with the in-situ carbonation/calcination of a CO(2) sorbent (dolomite) in a packed bed reactor under alternated feedstreams of fuel-steam and air. The fuel and steam conversion were higher with the sorbent present than without it. Initially, the dolomite carbonation was very efficient (100%), and 98% purity hydrogen was produced, but the carbonation decreased to around 56% with a purity of 95% respectively in the following cycles. Reduction of the nickel catalyst occurred alongside steam reforming, water gas shift and carbonation, with H(2) produced continuously under fuel-steam feeds. Catalyst and CO(2)-sorbent regeneration was observed, and long periods of autothermal operation within each cycle were demonstrated

[M(CO)4(2,2′-bipyridine)] (M = Cr, Mo, W) as efficient catalysts for electrochemical reduction of CO2 to CO at a gold electrode

Group 6 complexes of the type [M(CO)4(bpy)] (M=Cr, Mo, W) are capable of behaving as electrochemical catalysts for the reduction of CO2 at potentials less negative than those for the reduction of the radical anions [M(CO)4(bpy)].−. Cyclic voltammetric, chronoamperometric and UV/Vis/IR spectro-electrochemical data reveal that five-coordinate [M(CO)3(bpy)]2− are the active catalysts. The catalytic conversion is significantly more efficient in N-methyl-2-pyrrolidone (NMP) compared to tetrahydrofuran, which may reflect easier CO dissociation from 1e−-reduced [M(CO)4(bpy)].− in the former solvent, followed by second electron transfer. The catalytic cycle may also involve [M(CO)4(H-bpy)]− formed by protonation of [M(CO)3(bpy)]2−, especially in NMP. The strongly enhanced catalysis using an Au working electrode is remarkable, suggesting that surface interactions may play an important role, too

N-doped C dot/CoAl-layered double hydroxide/g-C3N4 hybrid composites for efficient and selective solar-driven conversion of CO2 into CH4

Converting CO 2 into value-added fuel by utilizing abundant solar energy could in principle minimize fossil fuel consumption and anthropogenic CO 2 emissions. However, developing catalytic systems with high selectivity and efficiency is necessary for photocatalytic CO 2 conversion. Here we report the fabrication of a N-doped C dot/CoAl-layered double hydroxide/g-C 3N 4 (NCD/LDH/CN) hybrid heterojunction photocatalyst for high efficiency and selectivity reduction of CO 2 with water into CH 4 under simulated-solar-light illumination. The NCD/LDH/CN hybrid photocatalyst demonstrated remarkable CH 4 production with an optimum rate of 25.69 μmol g −1 h −1, an apparent quantum yield of 0.62%, and 99% selectivity for CH 4. This NCD/LDH/CN hybrid system also exhibited exceptional stability and durability during consecutive test cycles with no apparent change in activity. The high activity and stability of the NCD/LDH/CN hybrid toward CO 2 photoreduction is essentially attributable to the strong synergy among the NCD, LDH, and CN constituents, which hinder charge recombination by accelerating charge transportation processes, together with the favorable properties such as broad optical response and good CO 2 adsorption capability. We explored the role of the NCDs in the NCD/LDH/CN hybrid system as a metal-free co-catalyst for the efficient and selective production of CH 4 from CO 2 photoreduction. Thus, the present report provides new insights into the rational fabrication of noble-metal-free photocatalysts for efficient and selective sustainable hydrocarbon production from photocatalytic reduction of CO 2. </p

Understanding the role of imidazolium-based ionic liquids in the electrochemical CO2 reduction reaction

The development of efficient CO 2 capture and utilization technologies driven by renewable energy sources is mandatory to reduce the impact of climate change. Herein, seven imidazolium-based ionic liquids (ILs) with different anions and cations were tested as catholytes for the CO2 electrocatalytic reduction to CO over Ag electrode. Relevant activity and stability, but different selectivities for CO2 reduction or the side H 2 evolution were observed. Density functional theory results show that depending on the IL anions the CO 2 is captured or converted. Acetate anions (being strong Lewis bases) enhance CO2 capture and H2 evolution, while fluorinated anions (being weaker Lewis bases) favour the CO2 electroreduction. Differently from the hydrolytically unstable 1-butyl-3-methylimidazolium tetrafluoroborate, 1-Butyl-3-Methylimidazolium Triflate was the most promising IL, showing the highest Faradaic efficiency to CO (>95%), and up to 8 h of stable operation at high current rates (−20 mA & −60 mA), which opens the way for a prospective process scale-up

Piezoelectric catalysis for efficient reduction of CO₂ using lead-free ferroelectric particulates

The increase in global energy demand, together with a rise in carbon dioxide (CO2) levels have encouraged research into the reduction of CO2 into useful chemicals and fuels. In this paper, we demonstrate the piezo-catalytic reduction of CO2 using lead-free lithium-doped potassium sodium niobate (KNN) ferroelectric ceramic particulates. The application of acoustic waves generated by ultrasound to a suspension of the ceramics particles creates pressure waves result in a large change in the spontaneous polarisation of the KNN particles via the piezoelectric effect, which in turn creates surfaces charges for CO2 reduction. The effect of CO2 gas concentration, the presence of dissolved species, and catalyst loading on piezo-catalytic performance are explored. By optimization of the piezo-catalytic effect, a promising piezo-catalytic CO2 reduction rate of 438 μmol g−1 h−1 is achieved, which is much larger than the those obtained from pyro-catalytic effects. This efficient and polarisation tuneable piezo-catalytic route has potential to promote the development of CO2 reduction via the utilisation of vibrational energy for environmental benefit.</p

Electrochemical Reduction Of Carbon Dioxide On Carbon Nanostructures: Defect Structures & Electrocatalytic Activity

The advantages of the electrochemical conversion of carbon dioxide to fuels using renewable energy sources are two-fold: (1) it has the potential to accomplish a carbon-neutral energy cycle and (2) it can provide an approach to tackle the environmental challenges caused by anthropogenic carbon dioxide emissions. Although thermodynamically possible, the kinetics of carbon dioxide reduction to fuels remains challenging and therefore, an efficient and robust electrocatalyst is needed to promote the reaction. The ideal catalyst for the electrochemical CO2 reduction must be capable of mediating multiple proton-coupled electron transfer reactions at low overpotentials, suppressing the concurrent hydrogen evolution reaction, converting CO2 to desired chemicals with high selectivity, and achieving long-term stability. Extensive research has been carried out on metallic electrocatalysts during the past three decades; however, none of these materials are simultaneously efficient and stable for practical purposes. This Ph.D. dissertation focuses on the investigation of the electro-reduction of CO2 on carbon nanostructures with a focus on understanding the relationship between defect structures and electrocatalytic activity. The initial focus of this work was to accomplish active performance and durability for electrosynthesis of fuels from CO2 using cost-effective catalysts. N-doped carbon nanotubes (NCNTs) were demonstrated as highly efficient, selective and more importantly, stable catalysts to achieve CO2 conversion to CO. The catalytic activity of these NCNTs was further benchmarked against other metallic catalysts reported in literature (Chapter 2). Compared to noble metals Ag & Au, these NCNTs exhibited a lower overpotential to achieve similar selectivity towards CO formation. The second part of this work was a study of the dependence of catalytic activity, i.e., the overpotential and selectivity for CO formation on the defect structures (pyridinic, graphitic, pyrrolic-N) inside NCNTs. The presence of both pyridinic and graphitic-N was found to significantly decrease the absolute overpotential and increase the selectivity towards CO formation (Chapter 3). The third part of this thesis work was to investigate CO2 reduction on N-doped graphene, in order to explore morphology effects on catalytic activity of NCNTs towards CO formation (Chapter 4). Overall, pyridinic-N defects exhibited the highest catalytic activity; thereby suggesting the directions for developing carbon nanostructures as metal-free electrocatalysts for CO2 reduction