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Conjugated Polymer/Recombinant Escherichia coli Biohybrid Systems for Photobiocatalytic Hydrogen Production. ACS NANO 2024. [PMID: 38739725 DOI: 10.1021/acsnano.3c10668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
Biohybrid photocatalysts are composite materials that combine the efficient light-absorbing properties of synthetic materials with the highly evolved metabolic pathways and self-repair mechanisms of biological systems. Here, we show the potential of conjugated polymers as photosensitizers in biohybrid systems by combining a series of polymer nanoparticles with engineered Escherichia coli cells. Under simulated solar light irradiation, the biohybrid system consisting of fluorene/dibenzo [b,d]thiophene sulfone copolymer (LP41) and recombinant E. coli (i.e., a LP41/HydA BL21 biohybrid) shows a sacrificial hydrogen evolution rate of 3.442 mmol g-1 h-1 (normalized to polymer amount). It is over 30 times higher than the polymer photocatalyst alone (0.105 mmol g-1 h-1), while no detectable hydrogen was generated from the E. coli cells alone, demonstrating the strong synergy between the polymer nanoparticles and bacterial cells. The differences in the physical interactions between synthetic materials and microorganisms, as well as redox energy level alignment, elucidate the trends in photochemical activity. Our results suggest that organic semiconductors may offer advantages, such as solution processability, low toxicity, and more tunable surface interactions with the biological components over inorganic materials.
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2
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Potential Dependent Reorientation Controlling Activity of a Molecular Electrocatalyst. J Am Chem Soc 2024; 146:7130-7134. [PMID: 38441442 PMCID: PMC10958496 DOI: 10.1021/jacs.3c13076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 02/26/2024] [Accepted: 02/26/2024] [Indexed: 03/21/2024]
Abstract
The activity of molecular electrocatalysts depends on the interplay of electrolyte composition near the electrode surface, the composition and morphology of the electrode surface, and the electric field at the electrode-electrolyte interface. This interplay is challenging to study and often overlooked when assessing molecular catalyst activity. Here, we use surface specific vibrational sum frequency generation (VSFG) spectroscopy to study the solvent and potential dependent activation of Mo(bpy)(CO)4, a CO2 reduction catalyst, at a polycrystalline Au electrode. We find that the parent complex undergoes potential dependent reorientation at the electrode surface when a small amount of N-methyl-2-pyrrolidone (NMP) is present. This preactivates the complex, resulting in greater yields at less negative potentials, of the active electrocatalyst for CO2 reduction.
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3
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Studying the cation dependence of CO 2 reduction intermediates at Cu by in situ VSFG spectroscopy. Chem Sci 2024; 15:2889-2897. [PMID: 38404396 PMCID: PMC10882457 DOI: 10.1039/d3sc05295h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 01/16/2024] [Indexed: 02/27/2024] Open
Abstract
The nature of the electrolyte cation is known to have a significant impact on electrochemical reduction of CO2 at catalyst|electrolyte interfaces. An understanding of the underlying mechanism responsible for catalytic enhancement as the alkali metal cation group is descended is key to guide catalyst development. Here, we use in situ vibrational sum frequency generation (VSFG) spectroscopy to monitor changes in the binding modes of the CO intermediate at the electrochemical interface of a polycrystalline Cu electrode during CO2 reduction as the electrolyte cation is varied. A CObridge mode is observed only when using Cs+, a cation that is known to facilitate CO2 reduction on Cu, supporting the proposed involvement of CObridge sites in CO coupling mechanisms during CO2 reduction. Ex situ measurements show that the cation dependent CObridge modes correlate with morphological changes of the Cu surface.
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4
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Unravelling the Roles of Integral Polypeptides in Excitation Energy Transfer of Photosynthetic RC-LH1 Supercomplexes. J Phys Chem B 2023; 127:7283-7290. [PMID: 37556839 PMCID: PMC10461223 DOI: 10.1021/acs.jpcb.3c04466] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Revised: 07/24/2023] [Indexed: 08/11/2023]
Abstract
Elucidating the photosynthetic processes that occur within the reaction center-light-harvesting 1 (RC-LH1) supercomplexes from purple bacteria is crucial for uncovering the assembly and functional mechanisms of natural photosynthetic systems and underpinning the development of artificial photosynthesis. Here, we examined excitation energy transfer of various RC-LH1 supercomplexes of Rhodobacter sphaeroides using transient absorption spectroscopy, coupled with lifetime density analysis, and studied the roles of the integral transmembrane polypeptides, PufX and PufY, in energy transfer within the RC-LH1 core complex. Our results show that the absence of PufX increases both the LH1 → RC excitation energy transfer lifetime and distribution due to the role of PufX in defining the interaction and orientation of the RC within the LH1 ring. While the absence of PufY leads to the conformational shift of several LH1 subunits toward the RC, it does not result in a marked change in the excitation energy transfer lifetime.
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5
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Pulsed Electrolysis with a Nickel Molecular Catalyst Improves Selectivity for Carbon Dioxide Reduction. J Am Chem Soc 2023. [PMID: 37404139 PMCID: PMC10360055 DOI: 10.1021/jacs.3c04811] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/06/2023]
Abstract
Pulsed electrolysis can significantly improve carbon dioxide reduction on metal electrodes, but the effect of short (millisecond to seconds) voltage steps on molecular electrocatalysts is largely unstudied. In this work, we investigate the effect pulse electrolysis has on the selectivity and stability of the homogeneous electrocatalyst [Ni(cyclam)]2+ at a carbon electrode. By tuning the potential and pulse duration, we achieve a significant improvement in CO Faradaic efficiencies (85%) after 3 h, double that of the system under potentiostatic conditions. The improved activity is due to in situ catalyst regeneration from an intermediate that occurs as part of the catalyst's degradation pathway. This study demonstrates the wider opportunity to apply pulsed electrolysis to molecular electrocatalysts to control activity and improve selectivity.
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6
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Packing-induced selectivity switching in molecular nanoparticle photocatalysts for hydrogen and hydrogen peroxide production. NATURE NANOTECHNOLOGY 2023; 18:307-315. [PMID: 36702952 DOI: 10.1038/s41565-022-01289-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Accepted: 11/07/2022] [Indexed: 06/18/2023]
Abstract
Molecular packing controls optoelectronic properties in organic molecular nanomaterials. Here we report a donor-acceptor organic molecule (2,6-bis(4-cyanophenyl)-4-(9-phenyl-9H-carbazol-3-yl)pyridine-3,5-dicarbonitrile) that exhibits two aggregate states in aqueous dispersions: amorphous nanospheres and ordered nanofibres with π-π molecular stacking. The nanofibres promote sacrificial photocatalytic H2 production (31.85 mmol g-1 h-1) while the nanospheres produce hydrogen peroxide (H2O2) (3.20 mmol g-1 h-1 in the presence of O2). This is the first example of an organic photocatalyst that can be directed to produce these two different solar fuels simply by changing the molecular packing. These different packings affect energy band levels, the extent of excited state delocalization, the excited state dynamics, charge transfer to O2 and the light absorption profile. We use a combination of structural and photophysical measurements to understand how this influences photocatalytic selectivity. This illustrates the potential to achieve multiple photocatalytic functionalities with a single organic molecule by engineering nanomorphology and solid-state packing.
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7
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Hybrid photocathode based on a Ni molecular catalyst and Sb 2Se 3 for solar H 2 production. Chem Commun (Camb) 2023; 59:944-947. [PMID: 36597867 DOI: 10.1039/d2cc04810h] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
We report a H2 evolving hybrid photocathode based on Sb2Se3 and a precious metal free molecular catalyst. Through the use of a high surface area TiO2 scaffold, we successfully increased the Ni molecular catalyst loading from 7.08 ± 0.43 to 45.76 ± 0.81 nmol cm-2, achieving photocurrents of 1.3 mA cm-2 at 0 V vs. RHE, which is 81-fold higher than the device without the TiO2 mesoporous layer.
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8
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Monitoring Interfacial Electric Fields at a Hematite Electrode During Water Oxidation . Chem Sci 2023; 14:3182-3189. [PMID: 36970076 PMCID: PMC10034152 DOI: 10.1039/d2sc05628c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Accepted: 02/23/2023] [Indexed: 02/25/2023] Open
Abstract
To understand the mechanisms of a water oxidation on materials such as hematite it is important that accurate measurements and models of the interfacial fields at the semiconductor liquid junction...
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Dynamics of Solid‐Electrolyte Interphase Formation on Silicon Electrodes Revealed by Combinatorial Electrochemical Screening. Angew Chem Int Ed Engl 2022; 61:e202207184. [PMID: 35699678 PMCID: PMC9543478 DOI: 10.1002/anie.202207184] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Indexed: 11/29/2022]
Abstract
Revealing how formation protocols influence the properties of the solid‐electrolyte interphase (SEI) on Si electrodes is key to developing the next generation of Li‐ion batteries. SEI understanding is, however, limited by the low‐throughput nature of conventional characterisation techniques. Herein, correlative scanning electrochemical cell microscopy (SECCM) and shell‐isolated nanoparticles for enhanced Raman spectroscopy (SHINERS) are used for combinatorial screening of the SEI formation under a broad experimental space (20 sets of different conditions with several repeats). This novel approach reveals the heterogeneous nature and dynamics of the SEI electrochemical properties and chemical composition on Si electrodes, which evolve in a characteristic manner as a function of cycle number. Correlative SECCM/SHINERS has the potential to screen thousands of candidate experiments on a variety of battery materials to accelerate the optimization of SEI formation methods, a key bottleneck in battery manufacturing.
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Photocatalytic Overall Water Splitting Under Visible Light Enabled by a Particulate Conjugated Polymer Loaded with Palladium and Iridium. Angew Chem Int Ed Engl 2022; 61:e202201299. [PMID: 35377540 PMCID: PMC9321674 DOI: 10.1002/anie.202201299] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Indexed: 11/27/2022]
Abstract
Polymer photocatalysts have received growing attention in recent years for photocatalytic hydrogen production from water. Most studies report hydrogen production with sacrificial electron donors, which is unsuitable for large‐scale hydrogen energy production. Here we show that the palladium/iridium oxide‐loaded homopolymer of dibenzo[b,d]thiophene sulfone (P10) facilitates overall water splitting to produce stoichiometric amounts of H2 and O2 for an extended period (>60 hours) after the system stabilized. These results demonstrate that conjugated polymers can act as single component photocatalytic systems for overall water splitting when loaded with suitable co‐catalysts, albeit currently with low activities. Transient spectroscopy shows that the IrO2 co‐catalyst plays an important role in the generation of the charge separated state required for water splitting, with evidence for fast hole transfer to the co‐catalyst.
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11
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Dynamics of Solid‐Electrolyte Interphase Formation on Silicon Electrodes Revealed by Combinatorial Electrochemical Screening. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202207184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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12
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Photocatalytic Overall Water Splitting Under Visible Light Enabled by a Particulate Conjugated Polymer Loaded with Palladium and Iridium**. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202201299] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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13
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Zero-Gap Bipolar Membrane Electrolyzer for Carbon Dioxide Reduction Using Acid-Tolerant Molecular Electrocatalysts. J Am Chem Soc 2022; 144:7551-7556. [PMID: 35451834 PMCID: PMC9074102 DOI: 10.1021/jacs.1c13024] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The scaling-up of electrochemical CO2 reduction requires circumventing the CO2 loss as carbonates under alkaline conditions. Zero-gap cell configurations with a reverse-bias bipolar membrane (BPM) represent a possible solution, but the catalyst layer in direct contact with the acidic environment of a BPM usually leads to H2 evolution dominating. Here we show that using acid-tolerant Ni molecular electrocatalysts selective (>60%) CO2 reduction can be achieved in a zero-gap BPM device using a pure water and CO2 feed. At a higher current density (100 mA cm-2), CO selectivity decreases, but was still >30%, due to reversible product inhibition. This study demonstrates the importance of developing acid-tolerant catalysts for use in large-scale CO2 reduction devices.
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Manganese Carbonyl Complexes as Selective Electrocatalysts for CO 2 Reduction in Water and Organic Solvents. Acc Chem Res 2022; 55:955-965. [PMID: 35285618 PMCID: PMC9007415 DOI: 10.1021/acs.accounts.1c00692] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
The electrochemical
reduction
of CO2 provides a way
to sustainably generate carbon-based fuels and feedstocks. Molecular
CO2 reduction electrocatalysts provide tunable reaction
centers offering an approach to control the selectivity of catalysis.
Manganese carbonyl complexes, based on [Mn(bpy)(CO)3Br]
and its derivatives (bpy = 2,2′-bipyridine), are particularly
interesting due to their ease of synthesis and the use of a first-row
earth-abundant transition metal. [Mn(bpy)(CO)3Br] was first
shown to be an active and selective catalyst for reducing CO2 to CO in organic solvents in 2011. Since then, manganese carbonyl
catalysts have been widely studied with numerous reports of their
use as electrocatalysts and photocatalysts and studies of their mechanism. This class of Mn catalysts only shows CO2 reduction
activity with the addition of weak Brønsted acids. Perhaps surprisingly,
early reports showed increased turnover frequencies as the acid strength
is increased without a loss in selectivity toward CO evolution. It
may have been expected that the competing hydrogen evolution
reaction could have led to lower selectivity. Inspired by these works
we began to explore if the catalyst would work in protic solvents,
namely, water, and to explore the pH range over which it can operate.
Here we describe the early studies from our laboratory that first
demonstrated the use of manganese carbonyl complexes in water and
then go on to discuss wider developments on the use of these catalysts
in water, highlighting their potential as catalysts for use in aqueous
CO2 electrolyzers. Key to the excellent selectivity
of these catalysts in the presence
of Brønsted acids is a proton-assisted CO2 binding
mechanism, where for the acids widely studied, lower pKa values actually favor CO2 binding over Mn–H
formation, a precursor to H2 evolution. Here we discuss
the wider literature before focusing on our own contributions in validating
this previously proposed mechanism through the use of vibrational
sum frequency generation (VSFG) spectroelectrochemistry. This allowed
us to study [Mn(bpy)(CO)3Br] while it is at, or near, the
electrode surface, which provided a way to identify new catalytic
intermediates and also confirm that proton-assisted CO2 binding operates in both the “dimer” and primary (via
[Mn(bpy)(CO)3]−) pathways. Understanding
the mechanism of how these highly selective catalysts operate is important
as we propose that the Mn complexes will be valuable models to guide
the development of new proton/acid tolerant CO2 reduction
catalysts.
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15
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Tuning the local chemical environment of ZnSe quantum dots with dithiols towards photocatalytic CO 2 reduction. Chem Sci 2022; 13:5988-5998. [PMID: 35685808 PMCID: PMC9132019 DOI: 10.1039/d2sc00890d] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 04/11/2022] [Indexed: 11/30/2022] Open
Abstract
Sunlight-driven CO2 reduction to renewable fuels is a promising strategy towards a closed carbon cycle in a circular economy. For that purpose, colloidal quantum dots (QDs) have emerged as a versatile light absorber platform that offers many possibilities for surface modification strategies. Considerable attention has been focused on tailoring the local chemical environment of the catalytic site for CO2 reduction with chemical functionalities ranging from amino acids to amines, imidazolium, pyridines, and others. Here we show that dithiols, a class of organic compounds previously unexplored in the context of CO2 reduction, can enhance photocatalytic CO2 reduction on ZnSe QDs. A short dithiol (1,2-ethanedithiol) activates the QD surface for CO2 reduction accompanied by a suppression of the competing H2 evolution reaction. In contrast, in the presence of an immobilized Ni(cyclam) co-catalyst, a longer dithiol (1,6-hexanedithiol) accelerates CO2 reduction. 1H-NMR spectroscopy studies of the dithiol-QD surface interactions reveal a strong affinity of the dithiols for the QD surface accompanied by a solvation sphere governed by hydrophobic interactions. Control experiments with a series of dithiol analogues (monothiol, mercaptoalcohol) render the hydrophobic chemical environment unlikely as the sole contribution of the enhancement of CO2 reduction. Density functional theory (DFT) calculations provide a framework to rationalize the observed dithiol length dependent activity through the analysis of the non-covalent interactions between the dangling thiol moiety and the CO2 reduction intermediates at the catalytic site. This work therefore introduces dithiol capping ligands as a straightforward means to enhance CO2 reduction catalysis on both bare and co-catalyst modified QDs by engineering the particle's chemical environment. ZnSe quantum dots (yellow sphere) are modified with dithiols of various lengths for enhanced visible light-driven CO2 to CO reduction in either the absence or presence of a molecular Ni co-catalyst.![]()
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Time-Resolved Raman Spectroscopy of Polaron Formation in a Polymer Photocatalyst. J Phys Chem Lett 2021; 12:10899-10905. [PMID: 34730969 PMCID: PMC8591663 DOI: 10.1021/acs.jpclett.1c03073] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 10/28/2021] [Indexed: 06/13/2023]
Abstract
Polymer photocatalysts are a synthetically diverse class of materials that can be used for the production of solar fuels such as H2, but the underlying mechanisms by which they operate are poorly understood. Time-resolved vibrational spectroscopy provides a powerful structure-specific probe of photogenerated species. Here we report the use of time-resolved resonance Raman (TR3) spectroscopy to study the formation of polaron pairs and electron polarons in one of the most active linear polymer photocatalysts for H2 production, poly(dibenzo[b,d]thiophene sulfone), P10. We identify that polaron-pair formation prior to thermalization of the initially generated excited states is an important pathway for the generation of long-lived photoelectrons.
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17
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Noncovalent immobilization of a nickel cyclam catalyst on carbon electrodes for CO2 reduction using aqueous electrolyte. Electrochim Acta 2021. [DOI: 10.1016/j.electacta.2021.139015] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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18
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Thermal catalytic conversion: general discussion. Faraday Discuss 2021; 230:124-151. [PMID: 34226907 DOI: 10.1039/d1fd90045e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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19
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Emerging technologies: general discussion. Faraday Discuss 2021; 230:388-412. [PMID: 34231609 DOI: 10.1039/d1fd90048j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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20
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Electrochemical carbon dioxide reduction in ionic liquids at high pressure. Faraday Discuss 2021; 230:331-343. [PMID: 34259680 DOI: 10.1039/d0fd00140f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Imidazolium ionic liquids are potentially useful solvents for both carbon dioxide reduction conversion and capture. In particular electrocatalytic CO2 reduction has been shown to occur at low overpotentials using a 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTf]) and water mixed solvent. A limitation of such solvent systems is their viscosity, making it hard to maintain reasonable catalytic current densities without energy intensive stirring/agitation of the electrolyte. Here we explore the electrochemical reduction of CO2 at high pressures (0.1 to 5.1 MPa) and demonstrate a correlation between the volume of expansion of the ionic liquid and the achieved catalytic current density. The improved electrocatalytic behaviour is proposed to be due to both the increased bulk CO2 concentration and the improved mass transport properties of the gas-expanded ionic liquid. These initial studies at pressure represent a step towards realising an integrated CO2 capture and utilisation system based around a common ionic liquid.
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21
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Hybrid Photocathodes for Carbon Dioxide Reduction: Interfaces for Charge Separation and Selective Catalysis. CHEMPHOTOCHEM 2021. [DOI: 10.1002/cptc.202000309] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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22
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Alkaline Water Oxidation Using a Bimetallic Phospho-Boride Electrocatalyst. CHEMSUSCHEM 2020; 13:6534-6540. [PMID: 33112493 DOI: 10.1002/cssc.202002269] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Revised: 10/16/2020] [Indexed: 06/11/2023]
Abstract
New oxygen evolution reaction (OER) electrocatalysts based on low-cost elements, which set new benchmark levels of activity, are vital if water electrolysis is to be applied on a global scale. Herein, a low-cost bimetallic phospho-boride catalyst was developed that showed outstanding OER activity of approximately 195 mV to achieve 10 mA cm-2 in alkaline water electrolysis, with a minimal catalyst loading of 0.3 mg cm-2 . The contrasting electron transfer property of the metal borides and phosphides when combined in phospho-boride modulated the electron density of the Co atom, yielding highly active CoOOH species at lower potentials. The addition of Mo at low levels further enhanced the activity by increasing the surface area and by formation of nano-crystalline domains. The combined contributions from each of the components resulted in a new benchmark mass activity of 666 A g-1 at 300 mV overpotential. This work presents a new avenue towards fabricating electrode materials with exceptional performances.
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Potential and pitfalls: On the use of transient absorption spectroscopy for in situ and operando studies of photoelectrodes. J Chem Phys 2020; 153:150901. [PMID: 33092350 DOI: 10.1063/5.0022138] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Here, we discuss the application, advantages, and potential pitfalls of using transient UV/Vis (ultraviolet-visible) absorption spectroscopy to study photoelectrodes for water splitting. We revisit one of the most commonly studied water oxidation photoanodes (α-Fe2O3-x) to provide commentary and guidelines on experiment design and data analysis for transient absorption (TA) studies of photoelectrodes within a photoelectrochemical cell. We also assess the applicability of such in situ TA studies to understand photoelectrodes under operating conditions. A major limitation is that most, if not all, past in situ TA studies have been carried out using only pulsed light sources to generate carriers, with the electrode held in the dark at other times, which is shown to be a poor model for operating conditions. However, with a simple modification of existing TA experiments, a simple operando TA measurement is reported.
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24
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Water Oxidation with Cobalt-Loaded Linear Conjugated Polymer Photocatalysts. Angew Chem Int Ed Engl 2020; 59:18695-18700. [PMID: 32596879 PMCID: PMC7589379 DOI: 10.1002/anie.202008000] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Indexed: 11/25/2022]
Abstract
The first examples of linear conjugated organic polymer photocatalysts that produce oxygen from water after loading with cobalt and in the presence of an electron scavenger are reported. The oxygen evolution rates, which are higher than for related organic materials, can be rationalized by a combination of the thermodynamic driving force for water oxidation, the light absorption of the polymer, and the aqueous dispersibility of the relatively hydrophilic polymer particles. We also used transient absorption spectroscopy to study the best performing system and we found that fast oxidative quenching of the exciton occurs (picoseconds) in the presence of an electron scavenger, minimizing recombination.
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25
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26
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Strong Impact of Intramolecular Hydrogen Bonding on the Cathodic Path of [Re(3,3'-dihydroxy-2,2'-bipyridine)(CO) 3Cl] and Catalytic Reduction of Carbon Dioxide. Inorg Chem 2020; 59:5564-5578. [PMID: 32237729 PMCID: PMC7175459 DOI: 10.1021/acs.inorgchem.0c00263] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Herein, we present the cathodic paths of the Group-7 metal complex [Re(3,3'-DHBPY)(CO)3Cl] (3,3'-DHBPY = 3,3'-dihydroxy-2,2'-bipyridine) producing a moderately active catalyst of electrochemical reduction of CO2 to CO. The combined techniques of cyclic voltammetry and IR/UV-vis spectroelectrochemistry have revealed significant differences in the chemistry of the electrochemically reduced parent complex compared to the previously published Re/4,4'-DHBPY congener. The initial irreversible cathodic step in weakly coordinating THF is shifted toward much less negative electrode potentials, reflecting facile reductive deprotonation of one hydroxyl group and strong intramolecular hydrogen bonding, O-H···O-. The latter process occurs spontaneously in basic dimethylformamide where Re/4,4'-DHBPY remains stable. The subsequent reduction of singly deprotonated [Re(3,3'-DHBPY-H+)(CO)3Cl]- under ambient conditions occurs at a cathodic potential close to that of the Re/4,4'-DHBPY-H+ derivative. However, for the stabilized 3,3'-DHBPY-H+ ligand, the latter process at the second cathodic wave is more complex and involves an overall transfer of three electrons. Rapid potential step electrolysis induces 1e--reductive cleavage of the second O-H bond, triggering dissociation of the Cl- ligand from [Re(3,3'-DHBPY-2H+)(CO)3Cl]2-. The ultimate product of the second cathodic step in THF was identified as 5-coordinate [Re(3,3'-DHBPY-2H+)(CO)3]3-, the equivalent of classical 2e--reduced [Re(BPY)(CO)3]-. Each reductive deprotonation of the DHBPY ligand results in a redshift of the IR ν(CO) absorption of the tricarbonyl complexes by ca. 10 cm-1, facilitating the product assignment based on comparison with the literature data for corresponding Re/BPY complexes. The Cl- dissociation from [Re(3,3'-DHBPY-2H+)(CO)3Cl]2- was proven in strongly coordinating butyronitrile. The latter dianion is stable at 223 K, converting at 258 K to 6-coordinate [Re(3,3'-DHBPY-2H+)(CO)3(PrCN)]3-. Useful reference data were obtained with substituted parent [Re(3,3'-DHBPY)(CO)3(PrCN)]+ that also smoothly deprotonates by the initial reduction to [Re(3,3'-DHBPY-H+)(CO)3(PrCN)]. The latter complex ultimately converts at the second cathodic wave to [Re(3,3'-DHBPY-2H+)(CO)3(PrCN)]3- via a counterintuitive ETC step generating the 1e- radical of the parent complex, viz., [Re(3,3'-DHBPY)(CO)3(PrCN)]. The same alternative reduction path is also followed by [Re(3,3'-DHBPY-H+)(CO)3Cl]- at the onset of the second cathodic wave, where the ETC step results in the intermediate [Re(3,3'-DHBPY)(CO)3Cl]•- further reducible to [Re(3,3'-DHBPY-2H+)(CO)3]3- as the CO2 catalyst.
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Water oxidation intermediates on iridium oxide electrodes probed by in situ electrochemical SHINERS. Chem Commun (Camb) 2020; 56:1129-1132. [DOI: 10.1039/c9cc08284k] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is applied to the study of a state-of-the-art water oxidation electrocatalyst, IrOx, during oxygen evolution.
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A stable covalent organic framework for photocatalytic carbon dioxide reduction. Chem Sci 2019; 11:543-550. [PMID: 32206271 PMCID: PMC7069507 DOI: 10.1039/c9sc03800k] [Citation(s) in RCA: 147] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Accepted: 11/20/2019] [Indexed: 12/22/2022] Open
Abstract
A metal-decorated alkene-linked covalent organic framework is a robust, selective photocatalyst for CO2 reduction.
Photocatalytic conversion of CO2 into fuels is an important challenge for clean energy research and has attracted considerable interest. Here we show that tethering molecular catalysts—a rhenium complex, [Re(bpy)(CO)3Cl]—together in the form of a crystalline covalent organic framework (COF) affords a heterogeneous photocatalyst with a strong visible light absorption, a high CO2 binding affinity, and ultimately an improved catalytic performance over its homogeneous Re counterpart. The COF incorporates bipyridine sites, allowing for ligation of the Re complex, into a fully π-conjugated backbone that is chemically robust and promotes light-harvesting. A maximum rate of 1040 μmol g–1 h–1 for CO production with 81% selectivity was measured. CO production rates were further increased up to 1400 μmol g–1 h–1, with an improved selectivity of 86%, when a photosensitizer was added. Addition of platinum resulted in production of syngas, hence, the co-formation of H2 and CO, the chemical composition of which could be adjusted by varying the ratio of COF to platinum. An amorphous analog of the COF showed significantly lower CO production rates, suggesting that crystallinity of the COF is beneficial to its photocatalytic performance in CO2 reduction.
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Abstract
Post-polymerization ladderization is explored as a promising technique to boost the photo-catalytic activity of conjugated polymers.
Conjugated ladder polymers (cLaPs) are introduced as organic semiconductors for photocatalytic hydrogen evolution from water under sacrificial conditions. Starting from a linear conjugated polymer (cLiP1), two ladder polymers are synthesized via post-polymerization annulation and oxidation techniques to generate rigidified, planarized materials bearing dibenzo[b,d]thiophene (cLaP1) and dibenzo[b,d]thiophene sulfone subunits (cLaP2). The high photocatalytic activity of cLaP1 (1307 μmol h–1 g–1) in comparison to that of cLaP2 (18 μmol h–1 g–1) under broadband illumination (λ > 295 nm) in the presence of a hole-scavenger is attributed to a higher yield of long-lived charges (μs to ms timescale), as evidenced by transient absorption spectroscopy. Additionally, cLaP1 has a larger overpotential for proton reduction and thus an increased driving force for the evolution of hydrogen under sacrificial conditions.
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Advanced Spectroelectrochemical Techniques to Study Electrode Interfaces Within Lithium-Ion and Lithium-Oxygen Batteries. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2019; 12:323-346. [PMID: 31038984 DOI: 10.1146/annurev-anchem-061318-115303] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Lithium battery technologies have revolutionized mobile energy storage, but improvements in the technology are still needed. Critical to delivering new light weight, high capacity, safe devices is an improved understanding of the dynamic processes occurring at the electrode-electrolyte interfaces. Therefore, alongside advances in materials there has been a parallel progression in advanced characterization methods. Herein, recent developments for operando spectro-electrochemical techniques centered on Raman, infrared, and sum frequency generation are described within the context of lithium-ion and non-aqueous lithium-oxygen battery research. In particular, shell-isolated nanoparticles for enhanced Raman spectroscopy (SHINERS), surface-enhanced infrared absorption spectroscopy (SEIRAS), and near-field infrared are explained and critically evaluated, and future opportunities discussed. The aim is to introduce the wider community to the developing range of methodologies and tools now available in the hope that it encourages greater usage across the sector.
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In situ study of the low overpotential "dimer pathway" for electrocatalytic carbon dioxide reduction by manganese carbonyl complexes. Phys Chem Chem Phys 2019; 21:7389-7397. [PMID: 30906938 DOI: 10.1039/c9cp00504h] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The electrocatalytic reduction of CO2 using [fac-Mn(bpy)(CO)3Br] (bpy = 2,2'-bipyridine) and its derivatives has been the subject of numerous recent studies. However the mechanisms of catalysis are still debated. Here we carry out in situ vibrational sum-frequency generation (VSFG) spectroelectrochemistry to examine how this catalyst behaves at an electrode surface. In particular, a low overpotential pathway involving a dimeric manganese has been reported in several studies using substituted bipyridine ligands. Here, we find that the "dimer pathway" can also occur with the unsubstuituted bipyridine complexes. Specifically we can observe spectroscopic evidence of the interaction between [Mn2(bpy)2(CO)6] with CO2 in the presence of a suitable acid. Detailed VSFG studies of [Mn2(bpy)2(CO)6], including of the potential dependence of the surface ν(CO) mode, allow us to construct a model of how it accumulates and behaves at the electrode surface under potentiostatic control.
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Vibrational sum-frequency generation spectroscopy of electrode surfaces: studying the mechanisms of sustainable fuel generation and utilisation. Phys Chem Chem Phys 2019; 21:12067-12086. [DOI: 10.1039/c9cp02225b] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The electrocatalytic oxidation of water coupled to the reduction of carbon dioxide, to make carbon based products, or the reduction of protons to provide hydrogen, offers a sustainable route to generating useful fuels.
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Gelation enabled charge separation following visible light excitation using self-assembled perylene bisimides. Phys Chem Chem Phys 2019; 21:26466-26476. [PMID: 31774419 DOI: 10.1039/c9cp05839g] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Perylene bisimides (PBIs) can be functionalised to enable controlled aggregation into complex supramolecular structures and are promising materials for photovoltaic and solar fuel applications.
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Detection of catalytic intermediates at an electrode surface during carbon dioxide reduction by an earth-abundant catalyst. Nat Catal 2018. [DOI: 10.1038/s41929-018-0169-3] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Directing the mechanism of CO 2 reduction by a Mn catalyst through surface immobilization. Phys Chem Chem Phys 2018; 20:6811-6816. [PMID: 29480315 DOI: 10.1039/c7cp08537k] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Immobilization of a Mn polypyridyl CO2 reduction electrocatalyst on nanocrystalline TiO2 electrodes yields an active heterogeneous system and also significantly triggers a change in voltammetric and catalytic behaviour, relative to in solution. A combination of spectroelectrochemical techniques are presented here to elucidate the mechanism of the immobilized catalyst in situ.
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ZnSe quantum dots modified with a Ni(cyclam) catalyst for efficient visible-light driven CO 2 reduction in water. Chem Sci 2018; 9:2501-2509. [PMID: 29732127 PMCID: PMC5911736 DOI: 10.1039/c7sc04429a] [Citation(s) in RCA: 100] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Accepted: 01/24/2018] [Indexed: 12/22/2022] Open
Abstract
A precious metal and Cd-free photocatalyst system for efficient CO2 reduction in water is reported. The hybrid assembly consists of ligand-free ZnSe quantum dots (QDs) as a visible-light photosensitiser combined with a phosphonic acid-functionalised Ni(cyclam) catalyst, NiCycP. This precious metal-free photocatalyst system shows a high activity for aqueous CO2 reduction to CO (Ni-based TONCO > 120), whereas an anchor-free catalyst, Ni(cyclam)Cl2, produced three times less CO. Additional ZnSe surface modification with 2-(dimethylamino)ethanethiol (MEDA) partially suppresses H2 generation and enhances the CO production allowing for a Ni-based TONCO of > 280 and more than 33% selectivity for CO2 reduction over H2 evolution, after 20 h visible light irradiation (λ > 400 nm, AM 1.5G, 1 sun). The external quantum efficiency of 3.4 ± 0.3% at 400 nm is comparable to state-of-the-art precious metal photocatalysts. Transient absorption spectroscopy showed that band-gap excitation of ZnSe QDs is followed by rapid hole scavenging and very fast electron trapping in ZnSe. The trapped electrons transfer to NiCycP on the ps timescale, explaining the high performance for photocatalytic CO2 reduction. With this work we introduce ZnSe QDs as an inexpensive and efficient visible light-absorber for solar fuel generation.
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Abstract
Graphitic carbon nitride (g-C3N4) synthesised from a urea precursor is an excellent CO2 reduction photocatalyst using [Co(bpy)n]2+ as a co-catalyst. A five-fold increase in activity for the highly polymerised urea derived g-C3N4 is achieved compared to alternative precursors. Transient absorption, time-resolved and steady-state emission studies indicate that the enhanced activity is related to both an increased driving force for photoelectron transfer and a greater availability of photogenerated charges.
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A Randomised Controlled Trial of a Universal Bonding Agent at Three Years: Self Etch vs Total Etch. THE EUROPEAN JOURNAL OF PROSTHODONTICS AND RESTORATIVE DENTISTRY 2017; 25:220-227. [PMID: 29182212 DOI: 10.1922/ejprd_01692burke08] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Accepted: 09/19/2017] [Indexed: 11/11/2022]
Abstract
General dental practice is increasingly being recognised as the ideal situation for the conduct of clinical trials into the longevity of restorations. The aim of this study was to investigate the survival of 64 nanofilled resin composite (Filtek Supreme XTE) restorations placed principally in loadbearing cavities using a Universal dentine bonding agent (Scotchbond Universal), in five UK dental practices by members of the UK-based practice-based research group, the PREP Panel. A split mouth design was used, comprising patients who required two restorations, with one of the restorations receiving a total etch approach using phosphoric acid and the other being placed using a self-etch approach. The results indicated good performance of the restorations examined, with no difference, in terms of marginal characteristics, between the restorations which received total etching and those which did not.
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Stable Ta2
O5
Overlayers on Hematite for Enhanced Photoelectrochemical Water Splitting Efficiencies. CHEMPHOTOCHEM 2017. [DOI: 10.1002/cptc.201700156] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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The Role of Electrode-Catalyst Interactions in Enabling Efficient CO 2 Reduction with Mo(bpy)(CO) 4 As Revealed by Vibrational Sum-Frequency Generation Spectroscopy. J Am Chem Soc 2017; 139:13791-13797. [PMID: 28895400 DOI: 10.1021/jacs.7b06898] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Group 6 metal carbonyl complexes ([M(bpy)(CO)4], M = Cr, Mo, W) are potentially promising CO2 reduction electrocatalysts. However, catalytic activity onsets at prohibitively negative potentials and is highly dependent on the nature of the working electrode. Here we report in situ vibrational SFG (VSFG) measurements of the electrocatalyst [Mo(bpy)(CO)4] at platinum and gold electrodes. The greatly improved onset potential for electrocatalytic CO2 reduction at gold electrodes is due to the formation of the catalytically active species [Mo(bpy)(CO)3]2- via a second pathway at more positive potentials, likely avoiding the need for the generation of [Mo(bpy)(CO)4]2-. VSFG studies demonstrate that the strength of the interaction between initially generated [Mo(bpy)(CO)4]•- and the electrode is critical in enabling the formation of the active catalyst via the low energy pathway. By careful control of electrode material, solvent and electrolyte salt, it should therefore be possible to attain levels of activity with group 6 complexes equivalent to their much more widely studied group 7 analogues.
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Abstract
Self-sorting between n-type and p-type gelators results in effective visible-active photoconductive xerogels.
We show that a perylene bisimide (PBI)-based gelator forms self-sorted mixtures with a stilbene-based gelator. To form the self-sorted gels, we use a slow pH change induced by the hydrolysis of glucono-δ-lactone (GdL) to gluconic acid. We prove that self-sorting occurs using NMR spectroscopy, UV-Vis spectroscopy, rheology, and viscometry. The corresponding xerogels are photoconductive. Importantly, the wavelength dependence of the photoconductive films is different to that of the films formed from the perylene bisimide alone. Transient absorption spectroscopy of the xerogels reveals changes in the spectrum of the PBI on the picosecond timescale in the presence of stilbene with a PBI radical anion being formed within 10 ps when the stilbene is present. The ability to form the PBI radical anion under visible light leads to the enhanced spectral response of the multicomponent gels. These systems therefore have potential as useful visible-active optoelectronics.
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Improving the efficiency of electrochemical CO2 reduction using immobilized manganese complexes. Faraday Discuss 2016; 183:147-60. [PMID: 26375151 DOI: 10.1039/c5fd00071h] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Immobilization of [Mn(bpy)(CO)3Br], (1) and [Mn(bpy((t)Bu)2)(CO)3Br] (2, where (bpy((t)Bu)2) = 4,4'-di-tert-butyl-2,2'-bipyridine) in Nafion/multi-walled carbon nanotubes (MWCNT) on glassy carbon yielded highly active electrodes for the reduction of CO2 to CO in aqueous solutions at pH 7. Films incorporating have significantly improved selectivity towards CO2, with CO : H2 ∼ 1 at -1.4 V vs. SCE, exceeding that for the previously reported /MWCNT/Nafion electrode. Furthermore, we report the synthesis and subsequent electrochemical characterization of two new substituted Mn(i) bipyridine complexes, [Mn(bpy(COOH)2)(CO)3Br] (3) and [Mn(bpy(OH)2)(CO)3Br] (4) (where (bpy(COOH)2) = 4,4'-di-carboxy-2,2'-bipyridine and (bpy(OH)2) = 4,4'-di-hydroxy-2,2'-bipyridine). Both 3 and 4 were found to have some activity towards CO2 in acetonitrile solutions; however once immobilized in Nafion membranes CO2 reduction was found to not occur at significant levels.
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Acid Treatment Enables Suppression of Electron-Hole Recombination in Hematite for Photoelectrochemical Water Splitting. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201510869] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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46
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Acid Treatment Enables Suppression of Electron-Hole Recombination in Hematite for Photoelectrochemical Water Splitting. Angew Chem Int Ed Engl 2016; 55:3403-7. [DOI: 10.1002/anie.201510869] [Citation(s) in RCA: 111] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Revised: 12/22/2015] [Indexed: 11/11/2022]
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Photochemical CO2 reduction in water using a co-immobilised nickel catalyst and a visible light sensitiser. Chem Commun (Camb) 2016; 52:14200-14203. [DOI: 10.1039/c6cc08590c] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Dye-sensitised photocatalytic CO2 reduction in water using an immobilised Nickel catalyst operates with efficiencies greatly exceeding the equivalent solution based system.
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A highly active nickel electrocatalyst shows excellent selectivity for CO 2 reduction in acidic media. Chem Sci 2015; 7:1521-1526. [PMID: 28808529 PMCID: PMC5530941 DOI: 10.1039/c5sc03225c] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 11/20/2015] [Indexed: 12/12/2022] Open
Abstract
The development of selective electrocatalysts for CO2 reduction in water offers a sustainable route to carbon based fuels and feedstocks.
The development of selective electrocatalysts for CO2 reduction in water offers a sustainable route to carbon based fuels and feedstocks. However, molecular catalysts are typically studied in non-aqueous solvents, in part to avoid competitive H2 evolution. [Ni(cyclam)]2+ (1) is one of the few known electrocatalysts that operate in water and 30 years after its report its activity remains a rarely surpassed benchmark. Here we report that [Ni(cyclam-CO2H)]2+ (cyclam-CO2H = 1,4,8,11-tetraazacyclotetradecane-6-carboxylic acid (2)) shows greatly enhanced activity versus1 for CO production. At pHs < pKa of the pendant carboxylic acid a large increase in catalytic activity occurs. Remarkably, despite the high proton concentration (pH 2), 2 maintains selectivity for CO2 reduction and is believed to be unique in operating selectively in such acidic aqueous solutions.
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Oxygen deficient α-Fe 2O 3 photoelectrodes: a balance between enhanced electrical properties and trap-mediated losses. Chem Sci 2015; 6:4009-4016. [PMID: 28717462 PMCID: PMC5497273 DOI: 10.1039/c5sc00423c] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Accepted: 04/28/2015] [Indexed: 12/18/2022] Open
Abstract
Intrinsic doping of hematite through the inclusion of oxygen vacancies (VO) is being increasingly explored as a simple, low temperature route to preparing active water splitting α-Fe2O3–x photoelectrodes.
Intrinsic doping of hematite through the inclusion of oxygen vacancies (VO) is being increasingly explored as a simple, low temperature route to preparing active water splitting α-Fe2O3–x photoelectrodes. Whilst it is widely accepted that the introduction of VO leads to improved conductivities, little else is verified regarding the actual mechanism of enhancement. Here we employ transient absorption (TA) spectroscopy to build a comprehensive kinetic model for water oxidation on α-Fe2O3–x. In contrast to previous suggestions, the primary effect of introducing VO is to block very slow (ms) surface hole – bulk electron recombination pathways. In light of our mechanistic research we are also able to identify and address a cause of the high photocurrent onset potential, a common issue with this class of electrodes. Atomic layer deposition (ALD) of Al2O3 is found to be particularly effective with α-Fe2O3–x, leading to the photocurrent onset potential shifting by ca. 200 mV. Significantly TA measurements on these ALD passivated electrodes also provide important insights into the role of passivating layers, that are relevant to the wider development of α-Fe2O3 photoelectrodes.
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A functionalised nickel cyclam catalyst for CO2 reduction: electrocatalysis, semiconductor surface immobilisation and light-driven electron transfer. Phys Chem Chem Phys 2015; 17:1562-6. [DOI: 10.1039/c4cp04871g] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Covalent immobilisation of a low cost electrocatalyst leads to an enhanced rate of photoelectron transfer from a light absorbing semiconductor.
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