scholarly journals Sulfur substitution in a Ni(cyclam) derivative results in lower overpotential for CO2 reduction and enhanced proton reduction

2019 ◽  
Vol 48 (18) ◽  
pp. 5923-5932 ◽  
Author(s):  
P. Gerschel ◽  
K. Warm ◽  
E. R. Farquhar ◽  
U. Englert ◽  
M. L. Reback ◽  
...  
Keyword(s):  
Co2 Reduction ◽  
Proton Reduction ◽  
Biologically Relevant ◽  
Cyclam Complexes ◽  
Lower Overpotential

N/S replacement in Ni-cyclam complexes highlights the importance of biologically relevant sulfur ligands in the CO2 and proton reduction.

An NADH-Inspired Redox Mediator Strategy to Promote Second-Sphere Electron and Proton Transfer for Cooperative Electrochemical CO2 Reduction Catalyzed by Iron Porphyrin

2020 ◽  
Author(s):  
Peter T. Smith ◽  
Sophia Weng ◽  
Christopher Chang
Keyword(s):  
Proton Transfer ◽  
Co2 Reduction ◽  
Iron Porphyrin ◽  
Redox Mediators ◽  
Reservoir Properties ◽  
Proton Reduction ◽  
Electrochemical Co2 Reduction ◽  
Starting Point ◽  
Rate Improvement ◽  
Molecular Catalysts

We present a bioinspired strategy for enhancing electrochemical carbon dioxide reduction catalysis by cooperative use of base-metal molecular catalysts with intermolecular second-sphere redox mediators that facilitate both electron and proton transfer. Functional synthetic mimics of the biological redox cofactor NADH, which are electrochemically stable and are capable of mediating both electron and proton transfer, can enhance the activity of an iron porphyrin catalyst for electrochemical reduction of CO<sub>2</sub> to CO, achieving a 13-fold rate improvement without altering the intrinsic high selectivity of this catalyst platform for CO<sub>2</sub> versus proton reduction. Evaluation of a systematic series of NADH analogs and redox-inactive control additives with varying proton and electron reservoir properties reveals that both electron and proton transfer contribute to the observed catalytic enhancements. This work establishes that second-sphere dual control of electron and proton inventories is a viable design strategy for developing more effective electrocatalysts for CO<sub>2</sub> reduction, providing a starting point for broader applications of this approach to other multi-electron, multi-proton transformations.

An NADH-Inspired Redox Mediator Strategy to Promote Second-Sphere Electron and Proton Transfer for Cooperative Electrochemical CO2 Reduction Catalyzed by Iron Porphyrin

2020 ◽  
Author(s):  
Peter T. Smith ◽  
Sophia Weng ◽  
Christopher Chang
Keyword(s):  
Proton Transfer ◽  
Co2 Reduction ◽  
Iron Porphyrin ◽  
Redox Mediators ◽  
Reservoir Properties ◽  
Proton Reduction ◽  
Electrochemical Co2 Reduction ◽  
Starting Point ◽  
Rate Improvement ◽  
Molecular Catalysts

We present a bioinspired strategy for enhancing electrochemical carbon dioxide reduction catalysis by cooperative use of base-metal molecular catalysts with intermolecular second-sphere redox mediators that facilitate both electron and proton transfer. Functional synthetic mimics of the biological redox cofactor NADH, which are electrochemically stable and are capable of mediating both electron and proton transfer, can enhance the activity of an iron porphyrin catalyst for electrochemical reduction of CO<sub>2</sub> to CO, achieving a 13-fold rate improvement without altering the intrinsic high selectivity of this catalyst platform for CO<sub>2</sub> versus proton reduction. Evaluation of a systematic series of NADH analogs and redox-inactive control additives with varying proton and electron reservoir properties reveals that both electron and proton transfer contribute to the observed catalytic enhancements. This work establishes that second-sphere dual control of electron and proton inventories is a viable design strategy for developing more effective electrocatalysts for CO<sub>2</sub> reduction, providing a starting point for broader applications of this approach to other multi-electron, multi-proton transformations.

scholarly journals Directing the reactivity of metal hydrides for selective CO2 reduction

2018 ◽  
Vol 115 (50) ◽  
pp. 12686-12691 ◽  
Author(s):  
Bianca M. Ceballos ◽  
Jenny Y. Yang
Keyword(s):  
High Selectivity ◽  
Co2 Reduction ◽  
Metal Hydrides ◽  
Product Formation ◽  
Proton Reduction ◽  
Efficient Catalyst ◽  
Faradaic Efficiency ◽  
Catalytic Intermediates ◽  
Proton Activity ◽  
Selection Of

A critical challenge in electrocatalytic CO2 reduction to renewable fuels is product selectivity. Desirable products of CO2 reduction require proton equivalents, but key catalytic intermediates can also be competent for direct proton reduction to H2. Understanding how to manage divergent reaction pathways at these shared intermediates is essential to achieving high selectivity. Both proton reduction to hydrogen and CO2 reduction to formate generally proceed through a metal hydride intermediate. We apply thermodynamic relationships that describe the reactivity of metal hydrides with H+ and CO2 to generate a thermodynamic product diagram, which outlines the free energy of product formation as a function of proton activity and hydricity (∆GH−), or hydride donor strength. The diagram outlines a region of metal hydricity and proton activity in which CO2 reduction is favorable and H+ reduction is suppressed. We apply our diagram to inform our selection of [Pt(dmpe)2](PF6)2 as a potential catalyst, because the corresponding hydride [HPt(dmpe)2]+ has the correct hydricity to access the region where selective CO2 reduction is possible. We validate our choice experimentally; [Pt(dmpe)2](PF6)2 is a highly selective electrocatalyst for CO2 reduction to formate (>90% Faradaic efficiency) at an overpotential of less than 100 mV in acetonitrile with no evidence of catalyst degradation after electrolysis. Our report of a selective catalyst for CO2 reduction illustrates how our thermodynamic diagrams can guide selective and efficient catalyst discovery.

Directing the Reactivity of Metal Hydrides for Selective CO2 Reduction

2018 ◽  
Author(s):  
Bianca M. Ceballos ◽  
Jenny Yang
Keyword(s):  
High Selectivity ◽  
Co2 Reduction ◽  
Metal Hydrides ◽  
Proton Reduction ◽  
Efficient Catalyst ◽  
Faradaic Efficiency ◽  
Pourbaix Diagrams ◽  
Catalytic Intermediates ◽  
Proton Activity ◽  
Selection Of

A critical challenge in electrocatalytic CO<sub>2</sub> reduction to renewable fuels is product selectivity. Desirable CO<sub>2</sub> reduction products require proton equivalents, but key catalytic intermediates in CO<sub>2</sub> reduction can also be competent for direct proton reduction to H<sub>2</sub>. Understanding how to manage divergent reaction pathways at these shared intermediates is essential to achieving high selectivity. Both proton reduction to hydrogen and CO<sub>2</sub> reduction to formate generally proceed through a metal hydride intermediate. We apply thermodynamic relationships that describe the reactivity of metal hydrides with H+ and CO<sub>2</sub> to generate a modified Pourbaix diagram which outlines product favorability as a function of pro-ton activity and hydricity (ΔG<sub>H-</sub>), or hydride donor strength. The diagram outlines a region of metal hydricity and proton activity in which CO2 reduction is favorable and H+ reduction is suppressed. We apply our diagram to inform our selection of [Pt(dmpe)<sub>2</sub>](PF<sub>6</sub>)<sub>2</sub> as a potential catalyst because the corresponding hydride [HPt(dmpe)<sub>2</sub>]+ has the correct hydricity to access the region where selective CO2 reduction is possible. We validate our choice experimentally; [Pt(dmpe)<sub>2</sub>](PF6)<sub>2</sub> is a highly selective electrocatalyst for CO<sub>2</sub> reduction to formate (>90 % Faradaic efficiency) at an overpotential of less than 100 mV with no evidence of catalyst degradation after electrolysis. Our report of a new selective catalyst for CO<sub>2</sub> reduction illustrates how our modified Pourbaix diagrams can guide selective and efficient catalyst discovery.

Construction of secondary coordination sphere boosts electrochemical CO2 reduction of iron porphyrins

2020 ◽  
Vol 24 (01n03) ◽  
pp. 465-472 ◽  
Author(s):  
Guiyu Liu ◽  
Ying-Jie Fan ◽  
Jun-Long Zhang
Keyword(s):  
Phenyl Ring ◽  
Co2 Reduction ◽  
Ortho Position ◽  
Iron Porphyrins ◽  
Reduction Of Iron ◽  
Electrochemical Co2 Reduction ◽  
Secondary Coordination Sphere ◽  
Turn Over Frequency ◽  
Turn Over ◽  
Lower Overpotential

Iron porphyrins with simple aminophenyl substitution are synthesized and their electrochemical CO[Formula: see text] reduction properties are studied. Fe-1, bearing an amino group in the ortho position of the phenyl ring exhibits an improved catalytic turn over frequency (TOF), lower overpotential and higher selectivity, compared with para-amino-substituted iron porphyrin (Fe-2) and the control iron tetraphenylporphyrin (Fe-3). DFT calculations also support the importance of hydrogen bonds on the reactivity of Fe-1, which facilitates the formation [Fe–CO[Formula: see text]][Formula: see text] adduct by lowering 1.45 kcal mol[Formula: see text].

scholarly journals CO2 reduction driven by a pH gradient

2020 ◽  
Author(s):  
Reuben Hudson ◽  
Ruvan de Graaf ◽  
Mari Strandoo Rodin ◽  
Aya Ohno ◽  
Nick Lane ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Hydrogen Oxidation ◽  
Co2 Reduction ◽  
Hydrothermal Systems ◽  
Ph Gradient ◽  
Ph Gradients ◽  
Biologically Relevant ◽  
Carbon Reduction ◽  
Geochemical Reactions ◽  
Direct Hydrogenation

AbstractAll life on Earth is built of organic molecules, so the primordial sources of reduced carbon are a major open question in studies of the origin of life. A variant of the alkaline-vent theory suggests that organics could have been produced by the reduction of CO2 via H2 oxidation, facilitated by geologically sustained pH gradients. The process would be an abiotic analog—and proposed evolutionary predecessor—of the modern Wood-Ljungdahl acetyl-Co-A pathway of extant archaea and bacteria. The first energetic bottleneck of the pathway involves the endergonic reduction of CO2 with H2 to formate, which has proven elusive in low-temperature abiotic settings. Here we show the reduction of CO2 with H2 at moderate pressures (1.5 bar), driven by microfluidic pH gradients across inorganic Fe(Ni)S precipitates. Isotopic labelling with 13C confirmed production of formate. Separately, deuterium (2H) labelling indicated that electron transfer to CO2 did not occur via direct hydrogenation with H2. Instead, freshly deposited Fe(Ni)S precipitates appear to facilitate electron transfer in an electrochemical-cell mechanism with two distinct half-reactions. Decreasing the pH gradient significantly, or removing either H2 or the precipitate, yielded no detectable product. Our work demonstrates the feasibility of spatially separated, yet electrically coupled geochemical reactions as drivers of otherwise endergonic processes. Beyond corroborating the ability of early-Earth alkaline hydrothermal systems to couple carbon reduction to hydrogen oxidation through geologically plausible and biologically relevant mechanisms, these results may also be of significance for industrial and environmental applications, where other redox reactions could be facilitated using similarly mild approaches.

scholarly journals CO2 reduction driven by a pH gradient

2020 ◽  
Vol 117 (37) ◽  
pp. 22873-22879 ◽  
Author(s):  
Reuben Hudson ◽  
Ruvan de Graaf ◽  
Mari Strandoo Rodin ◽  
Aya Ohno ◽  
Nick Lane ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Hydrogen Oxidation ◽  
Co2 Reduction ◽  
Isotopic Labeling ◽  
Hydrothermal Systems ◽  
Ph Gradient ◽  
Ph Gradients ◽  
Biologically Relevant ◽  
Carbon Reduction ◽  
Direct Hydrogenation

All life on Earth is built of organic molecules, so the primordial sources of reduced carbon remain a major open question in studies of the origin of life. A variant of the alkaline-hydrothermal-vent theory for life’s emergence suggests that organics could have been produced by the reduction of CO2 via H2 oxidation, facilitated by geologically sustained pH gradients. The process would be an abiotic analog—and proposed evolutionary predecessor—of the Wood–Ljungdahl acetyl-CoA pathway of modern archaea and bacteria. The first energetic bottleneck of the pathway involves the endergonic reduction of CO2 with H2 to formate (HCOO–), which has proven elusive in mild abiotic settings. Here we show the reduction of CO2 with H2 at room temperature under moderate pressures (1.5 bar), driven by microfluidic pH gradients across inorganic Fe(Ni)S precipitates. Isotopic labeling with 13C confirmed formate production. Separately, deuterium (2H) labeling indicated that electron transfer to CO2 does not occur via direct hydrogenation with H2 but instead, freshly deposited Fe(Ni)S precipitates appear to facilitate electron transfer in an electrochemical-cell mechanism with two distinct half-reactions. Decreasing the pH gradient significantly, removing H2, or eliminating the precipitate yielded no detectable product. Our work demonstrates the feasibility of spatially separated yet electrically coupled geochemical reactions as drivers of otherwise endergonic processes. Beyond corroborating the ability of early-Earth alkaline hydrothermal systems to couple carbon reduction to hydrogen oxidation through biologically relevant mechanisms, these results may also be of significance for industrial and environmental applications, where other redox reactions could be facilitated using similarly mild approaches.

scholarly journals Light-Driven CO2 Reduction by Co-Cytochrome b562

2021 ◽  
Vol 8 ◽  
Author(s):  
Rafael Alcala-Torano ◽  
Nicholas Halloran ◽  
Noah Gwerder ◽  
Dayn J. Sommer ◽  
Giovanna Ghirlanda
Keyword(s):  
Atmospheric Carbon Dioxide ◽  
Rational Design ◽  
Current Trend ◽  
Protoporphyrin Ix ◽  
Co2 Reduction ◽  
Proton Reduction ◽  
Carbon Dioxide Concentrations ◽  
Cobalt Protoporphyrin ◽  
Intrinsic Reactivity ◽  
Artificial Protein

The current trend in atmospheric carbon dioxide concentrations is causing increasing concerns for its environmental impacts, and spurring the developments of sustainable methods to reduce CO2 to usable molecules. We report the light-driven CO2 reduction in water in mild conditions by artificial protein catalysts based on cytochrome b562 and incorporating cobalt protoporphyrin IX as cofactor. Incorporation into the protein scaffolds enhances the intrinsic reactivity of the cobalt porphyrin toward proton reduction and CO generation. Mutations around the binding site modulate the activity of the enzyme, pointing to the possibility of further improving catalytic activity through rational design or directed evolution.

Directing the Reactivity of Metal Hydrides for Selective CO2 Reduction

2018 ◽  
Author(s):  
Bianca M. Ceballos ◽  
Jenny Yang
Keyword(s):  
High Selectivity ◽  
Co2 Reduction ◽  
Metal Hydrides ◽  
Proton Reduction ◽  
Efficient Catalyst ◽  
Faradaic Efficiency ◽  
Pourbaix Diagrams ◽  
Catalytic Intermediates ◽  
Proton Activity ◽  
Selection Of

A critical challenge in electrocatalytic CO<sub>2</sub> reduction to renewable fuels is product selectivity. Desirable CO<sub>2</sub> reduction products require proton equivalents, but key catalytic intermediates in CO<sub>2</sub> reduction can also be competent for direct proton reduction to H<sub>2</sub>. Understanding how to manage divergent reaction pathways at these shared intermediates is essential to achieving high selectivity. Both proton reduction to hydrogen and CO<sub>2</sub> reduction to formate generally proceed through a metal hydride intermediate. We apply thermodynamic relationships that describe the reactivity of metal hydrides with H+ and CO<sub>2</sub> to generate a modified Pourbaix diagram which outlines product favorability as a function of pro-ton activity and hydricity (ΔG<sub>H-</sub>), or hydride donor strength. The diagram outlines a region of metal hydricity and proton activity in which CO2 reduction is favorable and H+ reduction is suppressed. We apply our diagram to inform our selection of [Pt(dmpe)<sub>2</sub>](PF<sub>6</sub>)<sub>2</sub> as a potential catalyst because the corresponding hydride [HPt(dmpe)<sub>2</sub>]+ has the correct hydricity to access the region where selective CO2 reduction is possible. We validate our choice experimentally; [Pt(dmpe)<sub>2</sub>](PF6)<sub>2</sub> is a highly selective electrocatalyst for CO<sub>2</sub> reduction to formate (>90 % Faradaic efficiency) at an overpotential of less than 100 mV with no evidence of catalyst degradation after electrolysis. Our report of a new selective catalyst for CO<sub>2</sub> reduction illustrates how our modified Pourbaix diagrams can guide selective and efficient catalyst discovery.

scholarly journals Enhanced Electrocatalytic CO2 Reduction at Lower Overpotentials Using Iron (III) Tetra(thienyl)porphyrin

2019 ◽  
Author(s):  
Josh D. B. Koenig ◽  
Janina Willkomm ◽  
Roland Roesler ◽  
Warren Piers ◽  
Gregory C. Welch
Keyword(s):  
Electrochemical Properties ◽  
Co2 Reduction ◽  
Faradaic Efficiency ◽  
Lower Overpotential

Iron(III) tetra(5,10,15,20-thienyl)porphyrin chloride (FeTThP) is introduced as a new CO<sub>2</sub> reduction catalyst. The optical and electrochemical properties, as well as the CO<sub>2</sub> reduction capabilities of FeTThP are directly compared to those of iron(III) tetra(5,10,15,20-phenyl)porphyrin chloride (FeTPP). Relative to FeTPP, the newly developed FeTThP achieves a higher TON<sub>CO</sub>, with comparable faradaic efficiency, using a much lower overpotential.

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