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

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.

First-Principles DFT Insights into the Mechanisms of CO2 Reduction to CO on Fe (100)-Ni Bimetals

2021 ◽  
Author(s):  
Caroline Kwawu ◽  
Albert Aniagyei ◽  
Destiny Konadu ◽  
Elliot Menkah ◽  
Richard Tia
Keyword(s):  
Carbon Monoxide ◽  
Binding Site ◽  
Active Sites ◽  
Density Functional ◽  
Co2 Reduction ◽  
Density Functional Theory Calculations ◽  
Hydrocarbon Fuel ◽  
Generalized Gradient ◽  
Efficient Catalyst ◽  
Stepped Surface

Abstract Iron and nickel are known active sites in the enzyme carbon monoxide dehydrogenases (CODH) which catalyzes CO2 to CO reversibly. The presence of nickel impurities in the earth abundant iron surface could provide a more efficient catalyst for CO2 degradation into CO, which is a feedstock for hydrocarbon fuel production. In the present study, we have employed spin-polarized dispersion-corrected density functional theory calculations within the generalized gradient approximation to elucidate the active sites on Fe (100)-Ni bimetals. We sort to ascertain the mechanism of CO2 dissociation to carbon monoxide on Ni deposited and alloyed surfaces at 0.25, 0.50 and 1 monolayer (ML) impurity concentrations. CO2 and (CO + O) bind exothermically i.e., -0.87 eV and − 1.51 eV respectively to the bare Fe (100) surface with a decomposition barrier of 0.53 eV. The presence of nickel generally lowers the amount of charge transferred to CO2 moiety. Generally, the binding strengths of CO2 were reduced on the modified surfaces and the extent of its activation was lowered. The barriers for CO2 dissociation increased mainly upon introduction of Ni impurities which is undesired. However, the 0.5 ML deposited (FeNi0.5(A)) surface is promising for CO2 decomposition, providing a lower energy barrier (of 0.32 eV) than the pristine Fe (100) surface. This active 1-dimensional defective FeNi0.5(A) surface provides a stepped surface and Ni-Ni bridge binding site for CO2 on Fe (100). Ni-Ni bridge site on Fe (100) is more effective for both CO2 binding or sequestration and dissociation compared to the stepped surface providing the Fe-Ni bridge binding site.

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

2020 ◽  
Vol 10 (10) ◽  
pp. 3487 ◽  
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.

scholarly journals Folic Acid Self-Assembly Enabling Manganese Single-Atom Electrocatalyst for Selective Nitrogen Reduction to Ammonia

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Xuewan Wang ◽  
Dan Wu ◽  
Suyun Liu ◽  
Jiujun Zhang ◽  
Xian-Zhu Fu ◽  
...  
Keyword(s):  
Folic Acid ◽  
Self Assembly ◽  
Active Sites ◽  
Density Functional ◽  
Carbon Matrix ◽  
Single Atom ◽  
Synthesis Process ◽  
Ambient Conditions ◽  
Hydrogen Electrode ◽  
Faradaic Efficiency

AbstractEfficient and robust single-atom catalysts (SACs) based on cheap and earth-abundant elements are highly desirable for electrochemical reduction of nitrogen to ammonia (NRR) under ambient conditions. Herein, for the first time, a Mn–N–C SAC consisting of isolated manganese atomic sites on ultrathin carbon nanosheets is developed via a template-free folic acid self-assembly strategy. The spontaneous molecular partial dissociation enables a facile fabrication process without being plagued by metal atom aggregation. Thanks to well-exposed atomic Mn active sites anchored on two-dimensional conductive carbon matrix, the catalyst exhibits excellent activity for NRR with high activity and selectivity, achieving a high Faradaic efficiency of 32.02% for ammonia synthesis at  − 0.45 V versus reversible hydrogen electrode. Density functional theory calculations unveil the crucial role of atomic Mn sites in promoting N2 adsorption, activation and selective reduction to NH3 by the distal mechanism. This work provides a simple synthesis process for Mn–N–C SAC and a good platform for understanding the structure-activity relationship of atomic Mn sites. Graphic Abstract

scholarly journals Altering the rate-determining step over cobalt single clusters leading to highly efficient ammonia synthesis

2020 ◽  
Author(s):  
Sisi Liu ◽  
Mengfan Wang ◽  
Haoqing Ji ◽  
Xiaowei Shen ◽  
Chenglin Yan ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Ammonia Synthesis ◽  
Density Functional Theory Calculations ◽  
High Energy ◽  
Ambient Conditions ◽  
Property A ◽  
Strong Electron ◽  
Faradaic Efficiency ◽  
Rate Determining Step

Abstract Activation of high-energy triple-bonds of N2 is the most significant bottleneck of ammonia synthesis under ambient conditions. Here, by importing cobalt single clusters as strong electron-donating promoter into the catalyst, the rate-determining step of ammonia synthesis is altered to the subsequent proton addition so that the barrier of N2 dissociation can be successfully overcome. As revealed by density functional theory calculations, the N2 dissociation becomes exothermic over the cobalt single cluster upon the strong electron backdonation from metal to the N2 antibonding orbitals. The energy barrier of the positively shifted rate-determining step is also greatly reduced. At the same time, advanced sampling molecular dynamics simulations indicate a barrier-less process of the N2 approaching the active sites that greatly facilitates the mass transfer. With suitable thermodynamic and dynamic property, a high ammonia yield rate of 76.2 μg h–1 mg$^{-1 }_{\rm cat.}$ and superior Faradaic efficiency of 52.9% were simultaneously achieved.

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

2019 ◽  
Vol 10 (1) ◽  
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.

scholarly journals Selective CO-to-acetate electroproduction via intermediate adsorption tuning on ordered Cu-Pd sites

2020 ◽  
Author(s):  
Yali Ji ◽  
Zheng Chen ◽  
Chao Yang ◽  
Yuhang Wang ◽  
Jie Xu ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Membrane Electrode Assembly ◽  
Membrane Electrode ◽  
Acetate Production ◽  
Faradaic Efficiency ◽  
Potential Alternative ◽  
Acetate Formation ◽  
Pure Cu

Abstract Electrochemical reduction of carbon monoxide (CO) has recently been emerging as a potential alternative for converting carbon emission into high-value multi-carbon products such as acetate. Nonetheless, the activity and selectivity for producing acetate have remained low. Herein, we developed an atomically ordered copper-palladium intermetallic compound (CuPd-IC) structure that achieved a high Faradaic efficiency of 70 ± 5% for CO-to-acetate production with a partial current density of 425 mA·cm− 2. This corresponded to an acetate production rate of 4.0 mmol·h− 1·cm− 2, and 5.3 times of enhancement in acetate production compared to pure Cu. Structural characterizations and density functional theory calculations suggested that CuPd-IC presents a high density of Cu-Pd pairs that act as the active sites to enrich the surface CO coverage, stabilize the surface ethenone as a key acetate-path intermediate, and inhibit hydrogen evolution reaction, thus promoting acetate formation. Using a membrane electrode assembly device, the CuPd-IC catalyst enabled 100 hours of CO-to-acetate operation at 500 mA·cm− 2 and an average acetate Faradaic efficiency of 43%, producing ~ 2 mol acetate.

scholarly journals Selective reduction of CO to acetaldehyde with CuAg electrocatalysts

2020 ◽  
Vol 117 (23) ◽  
pp. 12572-12575 ◽  
Author(s):  
Lei Wang ◽  
Drew C. Higgins ◽  
Yongfei Ji ◽  
Carlos G. Morales-Guio ◽  
Karen Chan ◽  
...  
Keyword(s):  
Density Functional ◽  
Selective Reduction ◽  
Density Functional Theory Calculations ◽  
Hydrogen Electrode ◽  
Reaction Conditions ◽  
Faradaic Efficiency ◽  
Catalyst Composition ◽  
Alkaline Reaction ◽  
Fuels And Chemicals ◽  
Co Reduction

Electrochemical CO reduction can serve as a sequential step in the transformation of CO2into multicarbon fuels and chemicals. In this study, we provide insights on how to steer selectivity for CO reduction almost exclusively toward a single multicarbon oxygenate by carefully controlling the catalyst composition and its surrounding reaction conditions. Under alkaline reaction conditions, we demonstrate that planar CuAg electrodes can reduce CO to acetaldehyde with over 50% Faradaic efficiency and over 90% selectivity on a carbon basis at a modest electrode potential of −0.536 V vs. the reversible hydrogen electrode. The Faradaic efficiency to acetaldehyde was further enhanced to 70% by increasing the roughness factor of the CuAg electrode. Density functional theory calculations indicate that Ag ad-atoms on Cu weaken the binding energy of the reduced acetaldehyde intermediate and inhibit its further reduction to ethanol, demonstrating that the improved selectivity to acetaldehyde is due to the electronic effect from Ag incorporation. These findings will aid in the design of catalysts that are able to guide complex reaction networks and achieve high selectivity for the desired product.

scholarly journals Dynamic restructuring of coordinatively unsaturated copper paddle wheel clusters drives CO2 reduction efficiently

2021 ◽  
Author(s):  
Wei Zhang ◽  
Chuqiang Huang ◽  
Jiexin Zhu ◽  
Qiancheng Zhou ◽  
Ruohan Yu ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Structural Changes ◽  
Metal Organic Framework ◽  
Co2 Reduction ◽  
Density Functional Theory Calculations ◽  
Operating Conditions ◽  
Paddle Wheel ◽  
The Real ◽  
Metal Organic

Abstract Coordinatively unsaturated metal sites in metal–organic frameworks (MOFs) hold promises for improving activity and selectivity of catalyst. As the building unit of many MOFs, copper paddle-wheel (CPW) is of great interest to function as activity sites for CO2 reduction due to the ability of copper cations to attract and activate CO2 molecules. However, little is known about the real structure of these active sites for their dynamic structural changes under realistic operating conditions. Here, we apply to design defect metal−organic framework HKUST-1 with coordinatively unsaturated copper paddle wheel through a facile “atomized trimesic acid” strategy, reveal its dynamic behaviour during electrochemical reconstruction and prove its superior CO2 reduction activity. Through comprehensive analysis of various in situ spectroscopy characterizations, it is demonstrated that unsaturated copper paddle wheel clusters [CU-CPWC, Cu2(HCOO)3] are finally formed during electrochemical reconstruction and act as the real active sites. Mechanistic studies based on density functional theory calculations reveal that the higher d band center in CU-CPWC compared with that in CPW accelerates the electron transport from copper atoms to CO2 molecules, which can be exploited to improve the CO2 reduction performance.

In situ study of surface species and structure over Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction

2020 ◽  
Author(s):  
Chunjun Chen ◽  
Xupeng Yan ◽  
Yahui Wu ◽  
Shoujie Liu ◽  
Xiaofu Sun ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Isotope Labeling ◽  
Copper Catalysts ◽  
Surface Enhanced Raman Spectroscopy ◽  
Surface Species ◽  
Faradaic Efficiency ◽  
Electrochemical Co2 Reduction ◽  
Cu Catalysts

Abstract The oxide-derived copper (OD-Cu) has been discovered as effective catalyst for electroreduction of CO2 to C2+ products. The real structure of the OD-Cu and surface species in the reaction process are interesting phenomena, which are not clear now. Herein, in situ surface-enhanced Raman spectroscopy (SERS), operando X-ray absorption spectroscopy (XAS), 18O isotope labeling experiments, and density functional theory were employed to investigate the surface speciation and structure of the OD-Cu catalysts during CO2 electroreduction. It was found that the OD-Cu catalysts were reduced to metallic Cu(0) in the reaction. CuOx species existed on the catalyst surfaces during CO2RR, which resulted from the chemisorption of CO2 instead of active sites of the catalyst. After removing potential, Cu2O was formed on the surface of the catalyst by reaction of Cu and H2O. It was also found that Cu (100) facet can be enhanced by redox cycling treatment of the catalyst, leading to outstanding performance of the catalyst. The Faradaic efficiency(FE) for C2+ products reached up to 83.8% at current density of 341.5 mA•cm-2 at -0.9 V vs RHE. The findings of this work are very interesting knowledge in the area in electrochemical reduction of CO2. The work also demonstrates advantage and necessity of in situ experimental methods in exploring the interesting phenomena in the process of CO2RR.

Field Effect Modulation of Electrocatalytic Hydrogen Evolution at Back-Gated Two-Dimensional MoS2 Electrodes

2019 ◽  
Author(s):  
Yan Wang ◽  
Sagar Udyavara ◽  
Matthew Neurock ◽  
C. Daniel Frisbie
Keyword(s):  
Electric Field ◽  
Hydrogen Evolution ◽  
Active Sites ◽  
Density Functional ◽  
Electrode Materials ◽  
Density Functional Theory Calculations ◽  
Electronic Charge ◽  
Back Side ◽  
Gate Electrode ◽  
Conventional Manner

<div> <div> <div> <p> </p><div> <div> <div> <p>Electrocatalytic activity for hydrogen evolution at monolayer MoS2 electrodes can be enhanced by the application of an electric field normal to the electrode plane. The electric field is produced by a gate electrode lying underneath the MoS2 and separated from it by a dielectric. Application of a voltage to the back-side gate electrode while sweeping the MoS2 electrochemical potential in a conventional manner in 0.5 M H2SO4 results in up to a 140-mV reduction in overpotential for hydrogen evolution at current densities of 50 mA/cm2. Tafel analysis indicates that the exchange current density is correspondingly improved by a factor of 4 to 0.1 mA/cm2 as gate voltage is increased. Density functional theory calculations support a mechanism in which the higher hydrogen evolution activity is caused by gate-induced electronic charge on Mo metal centers adjacent the S vacancies (the active sites), leading to enhanced Mo-H bond strengths. Overall, our findings indicate that the back-gated working electrode architecture is a convenient and versatile platform for investigating the connection between tunable electronic charge at active sites and overpotential for electrocatalytic processes on ultrathin electrode materials.</p></div></div></div><br><p></p></div></div></div>

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