Electron-Reservoir Effect on a Perylene Diimide Tethered Rhenium Bipyridine Complex for CO2 Reduction

Here we report on a molecular catalyst with a built-in electron-reservoir for enhanced CO2 conversion. The synthesis and characterization of this N-annulated perylene diimide (PDI) photosensitized Re(bpy) supramolecular dyad [Re(bpy-TAz-PDI)], as well as successful electro- and photocatalytic CO2-to-CO conversion, are detailed herein. Upon electrochemical reduction in the presence of CO2 and a proton source, Re(bpy-TAz-PDI) exhibited significant current enhancement, where the onset of electrocatalytic CO2 reduction for Re(bpy-TAz-PDI) occurred at a much less negative potential than standard Re(bpy) complexes. At an applied potential of -1.8 V vs. Fc+/0, 400 mV lower than the benchmark Re(dmbpy) catalyst, Re(bpy-TAz-PDI) was able to achieve the same catalytic activity (TONco = 24) and Faradaic efficiency (FE = 92 %) during controlled potential electrolysis (CPE) experiments. Through a combination of UV-visible-nearIR spectroelectrochemistry (SEC), FTIR SEC, and chemical reduction experiments, it was shown that the PDI-moiety served as an electron-reservoir for Re(bpy), thereby allowing catalytic activity at lower overpotentials. Density functional theory (DFT) studies probing the optimized geometries, frontier molecular orbitals, and spin-densities of various catalytic intermediates revealed that the geometric configuration of PDI, relative to the Re(bpy)-moiety, plays a critical role in accessing electrons from the electron-reservoir. The near identical performance of Re(bpy-TAz-PDI) at lower overpotentials relative to the benchmark Re(dmbpy) catalyst highlights the utility of organic chromophore electron-reservoirs as a method for lowering the required overpotential for CO2 conversion.

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Improving the Catalytic CO2 Reduction on Cs2AgBiBr6 by Halide Defect Engineering: A DFT Study

Materials ◽

10.3390/ma14102469 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2469

Author(s):

Pengfei Chen ◽

Yiao Huang ◽

Zuhao Shi ◽

Xingzhu Chen ◽

Neng Li

Keyword(s):

Gas Adsorption ◽

Catalytic Reduction ◽

Deep Level ◽

Critical Role ◽

Co2 Reduction ◽

First Principles Calculation ◽

Bandgap Energy ◽

Practical Implementation ◽

Co2 Conversion ◽

Defect Engineering

Pb-free double halide perovskites have drawn immense attention in the potential photocatalytic application, due to the regulatable bandgap energy and nontoxicity. Herein, we first present a study for CO2 conversion on Pb-free halide perovskite Cs2AgBiBr6 under state-of-the-art first-principles calculation with dispersion correction. Compared with the previous CsPbBr3, the cell parameter of Cs2AgBiBr6 underwent only a small decrease of 3.69%. By investigating the adsorption of CO, CO2, NO, NO2, and catalytic reduction of CO2, we found Cs2AgBiBr6 exhibits modest adsorption ability and unsatisfied potential determining step energy of 2.68 eV in catalysis. We adopted defect engineering (Cl doping, I doping and Br-vacancy) to regulate the adsorption and CO2 reduction behavior. It is found that CO2 molecule can be chemically and preferably adsorbed on Br-vacancy doped Cs2AgBiBr6 with a negative adsorption energy of −1.16 eV. Studying the CO2 reduction paths on pure and defect modified Cs2AgBiBr6, Br-vacancy is proved to play a critical role in decreasing the potential determining step energy to 1.25 eV. Finally, we probe into the electronic properties and demonstrate Br-vacancy will not obviously promote the process of catalysis deactivation, as there is no formation of deep-level electronic states acting as carrier recombination center. Our findings reveal the process of gas adsorption and CO2 reduction on novel Pb-free Cs2AgBiBr6, and propose a potential strategy to improve the efficiency of catalytic CO2 conversion towards practical implementation.

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Clam-shaped cyclam-functionalized porphyrin for electrochemical reduction of carbon dioxide

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424619500548 ◽

2019 ◽

Vol 23 (04n05) ◽

pp. 453-461

Author(s):

Sumana Tawil ◽

Hathaichanok Seelajaroen ◽

Amorn Petsom ◽

Niyazi Serdar Sariciftci ◽

Patchanita Thamyongkit

Keyword(s):

Carbon Dioxide ◽

Carbon Monoxide ◽

Cyclic Voltammetry ◽

Catalytic Activity ◽

Electrochemical Reduction ◽

Target Compound ◽

Faradaic Efficiency ◽

Controlled Potential Electrolysis ◽

Improved Stability ◽

Controlled Potential

A clam-shaped molecule comprising a Zn(II)-porphyrin and a Zn(II)-cyclam is synthesized and characterized. Its electrochemical behavior and catalytic activity for homogeneous electrochemical reduction of carbon dioxide (CO[Formula: see text] are investigated by cyclic voltammetry and compared with those of Zn(II)-meso-tetraphenylporphyrin and Zn(II)-cyclam. Under N2-saturated conditions, cyclic voltammetry of the featured complex has characteristics of its two constituents, but under CO2-saturated conditions, the target compound exhibits significant current enhancement. Iterative reduction under electrochemical conditions indicated the target compound has improved stability relative to Zn(II)-cyclam. Controlled potential electrolysis demonstrates that, without addition of water, methane (CH[Formula: see text] is the only detectable product with 1% Faradaic efficiency (FE). The formation of CH4 is not observed under the catalysis of the Zn(II)-porphyrin benchmark compound, indicating that the CO2-capturing function of the Zn(II)-cyclam unit contributes to the catalysis. Upon addition of 3% v/v water, the electrochemical reduction of CO2 in the presence of the target compound gives carbon monoxide (CO) with 28% FE. Dominance of CO formation under these conditions suggests enhancement of proton-coupled reduction. Integrated action of these Zn(II)-porphyrin and Zn(II)-cyclam units offers a notable example of a molecular catalytic system where the cyclam ring captures and brings CO2 into the proximity of the porphyrin catalysis center.

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Photoelectrochemical Reduction of CO2 to Syngas by Reduced Ag Catalysts on Si Photocathodes

Applied Sciences ◽

10.3390/app10103487 ◽

2020 ◽

Vol 10 (10) ◽

pp. 3487 ◽

Cited By ~ 1

Author(s):

Changyeon Kim ◽

Seokhoon Choi ◽

Min-Ju Choi ◽

Sol A Lee ◽

Sang Hyun Ahn ◽

...

Keyword(s):

Catalytic Activity ◽

Active Sites ◽

Co2 Reduction ◽

Reduction Reaction ◽

Hydrogen Electrode ◽

Faradaic Efficiency ◽

Onset Potential ◽

Reduction Of Co2 ◽

Co2 Reduction Reaction ◽

Ag Catalysts

The photoelectrochemical reduction of CO2 to syngas that is used for many practical applications has been emerging as a promising technique to relieve the increase of CO2 in the atmosphere. Si has been considered to be one of the most promising materials for photoelectrodes, but the integration of electrocatalysts is essential for the photoelectrochemical reduction of CO2 using Si. We report an enhancement of catalytic activity for CO2 reduction reaction by Ag catalysts of tuned morphology, active sites, and electronic structure through reducing anodic treatment. Our proposed photocathode structure, a SiO2 patterned p-Si photocathode with these reduced Ag catalysts, that was fabricated using electron-beam deposition and electrodeposition methods, provides a low onset-potential of −0.16 V vs. the reversible hydrogen electrode (RHE), a large saturated photocurrent density of −9 mA/cm2 at −1.23 V vs. RHE, and faradaic efficiency for CO of 47% at −0.6 V vs. RHE. This photocathode can produce syngas in the ratio from 1:1 to 1:3, which is an appropriate proportion for practical application. This work presents a new approach for designing photocathodes with a balanced catalytic activity and light absorption to improve the photoelectrochemical application for not only CO2 reduction reaction, but also water splitting or N2 reduction reaction.

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In Search of the Active Sites for the Selective Catalytic Reduction on Tungsten-Doped Vanadia Monolayer Catalysts supported by TiO2

10.26434/chemrxiv.14363567.v1 ◽

2021 ◽

Author(s):

Mengru Li ◽

Sung Sakong ◽

Axel Gross

Keyword(s):

Catalytic Activity ◽

Selective Catalytic Reduction ◽

Active Sites ◽

Density Functional ◽

Catalytic Reduction ◽

Computational Study ◽

Critical Role ◽

Operating Conditions ◽

High Catalytic Activity ◽

Atomistic Structure

Tungsten-doped vanadia-based catalysts supported on anatase TiO2 are used to reduce hazardous NO emissions through the selective catalytic reduction of ammonia, but their exact atomistic structure is still largely unknown. In this computational study, the atomistic structure of mixed tungsta-vanadia monolayers on TiO2 support under typical operating conditions has been addressed by periodic density functional theory calculations. The chemical environment has been taken into account in a grand-canonical approach. We evaluate the stable catalyst structures as a function of the oxygen chemical potential and vanadium and tungsten concentrations. Thus we determine structural motifs of tungsta-vanadia/TiO2 catalysts that are stable under operating conditions. Furthermore, we identify active sites that promise high catalytic activity for the selective catalytic reduction by ammonia. Our calculations reveal the critical role of the stoichiometry of the tungsta-vanadia layers with respect to their catalytic activity in the selective catalytic reduction.

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Fast operando spectroscopy tracking in situ generation of rich defects in silver nanocrystals for highly selective electrochemical CO2 reduction

Nature Communications ◽

10.1038/s41467-021-20960-8 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Xinhao Wu ◽

Yanan Guo ◽

Zengsen Sun ◽

Fenghua Xie ◽

Daqin Guan ◽

...

Keyword(s):

Active Sites ◽

Density Functional ◽

Co2 Reduction ◽

Density Functional Theory Calculations ◽

Defect Concentration ◽

Hydrogen Electrode ◽

Efficient Catalyst ◽

Faradaic Efficiency ◽

Electrochemical Co2 Reduction ◽

Cell Reactor

AbstractElectrochemical CO2 reduction (ECR) is highly attractive to curb global warming. The knowledge on the evolution of catalysts and identification of active sites during the reaction is important, but still limited. Here, we report an efficient catalyst (Ag-D) with suitable defect concentration operando formed during ECR within several minutes. Utilizing the powerful fast operando X-ray absorption spectroscopy, the evolving electronic and crystal structures are unraveled under ECR condition. The catalyst exhibits a ~100% faradaic efficiency and negligible performance degradation over a 120-hour test at a moderate overpotential of 0.7 V in an H-cell reactor and a current density of ~180 mA cm−2 at −1.0 V vs. reversible hydrogen electrode in a flow-cell reactor. Density functional theory calculations indicate that the adsorption of intermediate COOH could be enhanced and the free energy of the reaction pathways could be optimized by an appropriate defect concentration, rationalizing the experimental observation.

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Atomic-thin hexagonal CuCo nanocrystals with d-band tuning for CO2 reduction

Journal of Materials Chemistry A ◽

10.1039/d0ta12022g ◽

2021 ◽

Vol 9 (12) ◽

pp. 7496-7502

Author(s):

Yibo Yan ◽

Zhengping Zhao ◽

Jun Zhao ◽

Wenfei Tang ◽

Wei Huang ◽

...

Keyword(s):

Density Functional Theory ◽

Binding Energy ◽

Density Functional ◽

Co2 Reduction ◽

Functional Theory ◽

Faradaic Efficiency

Hexagonal CuCo nanocrystals are exploited for CO2 reduction at high faradaic efficiency. Density functional theory calculates the structure-oriented binding energy of intermediates for catalyst optimization.

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Isolated copper–tin atomic interfaces tuning electrocatalytic CO2 conversion

Nature Communications ◽

10.1038/s41467-021-21750-y ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Wenhao Ren ◽

Xin Tan ◽

Jiangtao Qu ◽

Sesi Li ◽

Jiantao Li ◽

...

Keyword(s):

Surface Science ◽

Interface Design ◽

Density Functional ◽

High Surface ◽

Critical Role ◽

Single Atom ◽

Surface Alloys ◽

Functional Theory ◽

Faradaic Efficiency ◽

Pure Cu

AbstractDirect experimental observations of the interface structure can provide vital insights into heterogeneous catalysis. Examples of interface design based on single atom and surface science are, however, extremely rare. Here, we report Cu–Sn single-atom surface alloys, where isolated Sn sites with high surface densities (up to 8%) are anchored on the Cu host, for efficient electrocatalytic CO2 reduction. The unique geometric and electronic structure of the Cu–Sn surface alloys (Cu97Sn3 and Cu99Sn1) enables distinct catalytic selectivity from pure Cu100 and Cu70Sn30 bulk alloy. The Cu97Sn3 catalyst achieves a CO Faradaic efficiency of 98% at a tiny overpotential of 30 mV in an alkaline flow cell, where a high CO current density of 100 mA cm−2 is obtained at an overpotential of 340 mV. Density functional theory simulation reveals that it is not only the elemental composition that dictates the electrocatalytic reactivity of Cu–Sn alloys; the local coordination environment of atomically dispersed, isolated Cu–Sn bonding plays the most critical role.

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Colloidal silver diphosphide (AgP2) nanocrystals as low overpotential catalysts for CO2 reduction to tunable syngas

Nature Communications ◽

10.1038/s41467-019-13388-8 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 10

Author(s):

Hui Li ◽

Peng Wen ◽

Dominique S. Itanze ◽

Zachary D. Hood ◽

Xiao Ma ◽

...

Keyword(s):

Density Functional ◽

Co2 Reduction ◽

Intermediate Formation ◽

Density Functional Theory Calculations ◽

Photocurrent Density ◽

Faradaic Efficiency ◽

Onset Potential ◽

Fold Reduction ◽

Co Conversion ◽

Co Reduction

AbstractProduction of syngas with tunable CO/H2 ratio from renewable resources is an ideal way to provide a carbon-neutral feedstock for liquid fuel production. Ag is a benchmark electrocatalysts for CO2-to-CO conversion but high overpotential limits the efficiency. We synthesize AgP2 nanocrystals (NCs) with a greater than 3-fold reduction in overpotential for electrochemical CO2-to-CO reduction compared to Ag and greatly enhanced stability. Density functional theory calculations reveal a significant energy barrier decrease in the formate intermediate formation step. In situ X-ray absorption spectroscopy (XAS) shows that a maximum Faradaic efficiency is achieved at an average silver valence state of +1.08 in AgP2 NCs. A photocathode consisting of a n+p-Si wafer coated with ultrathin Al2O3 and AgP2 NCs achieves an onset potential of 0.2 V vs. RHE for CO production and a partial photocurrent density for CO at −0.11 V vs. RHE (j−0.11, CO) of −3.2 mA cm−2.

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Fabrication of Large Area Ag Gas Diffusion Electrode via Electrodeposition for Electrochemical CO2 Reduction

Coatings ◽

10.3390/coatings10040341 ◽

2020 ◽

Vol 10 (4) ◽

pp. 341

Author(s):

Seonhwa Oh ◽

Hyanjoo Park ◽

Hoyoung Kim ◽

Young Sang Park ◽

Min Gwan Ha ◽

...

Keyword(s):

Co2 Reduction ◽

Gas Diffusion ◽

Gas Diffusion Electrode ◽

Carbon Paper ◽

Membrane Electrode ◽

Co2 Conversion ◽

Large Area ◽

Faradaic Efficiency ◽

Electrochemical Co2 Reduction ◽

Galvanostatic Deposition

For the improvement for the commercialization of electrochemical carbon dioxide (CO2) conversion technology, it is important to develop a large area Ag gas diffusion electrode (GDE), that exhibits a high electrochemical CO2 conversion efficiency and high cell performance in a membrane electrode assembly (MEA)-type CO2 electrolyzer. In this study, the electrodeposition of Ag on a carbon-paper gas diffusion layer was performed to fabricate a large area (25.5 and 136 cm2) Ag GDE for application to an MEA-type CO2 electrolyzer. To achieve uniformity throughout this large area, an optimization of the electrodeposition variables, such as the electrodes system, electrodes arrangement, deposition current and deposition time was performed with respect to the total electrolysis current, CO production current, Faradaic efficiency (FE), and deposition morphology. The optimal conditions, that is, galvanostatic deposition at 0.83 mA/cm2 for 50 min in a horizontal, two-electrode system with a working-counter electrode distance of 4 cm, did ensure a uniform performance throughout the electrode. The position-averaged CO current densities of 2.72 and 2.76 mA/cm2 and FEs of 83.78% (with a variation of 3.25%) and 82.78% (with a variation of 8.68%) were obtained for 25.5 and 136 cm2 Ag GDEs, respectively. The fabricated 136 cm2 Ag GDE was further used in MEA-type CO2 electrolyzers having an active geometric area of 107.44 cm2, giving potential-dependent CO conversion efficiencies of 41.99%–57.75% at Vcell = 2.2–2.6 V.

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