scholarly journals Size Dependent CO2 Reduction Activity of Ag Nanoparticle Electrocatalysts

2021 ◽  
Author(s):  
Xingyi Deng ◽  
Dominic Alfonso ◽  
Thuy-Duong Nguyen-Phan ◽  
Douglas Kauffman
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Particle Diameter ◽  
Small Diameter ◽  
Co2 Reduction ◽  
High Population ◽  
Structure Property ◽  
Size Dependent ◽  
Catalyst Utilization ◽  
Ag Catalysts

Abstract Coinage metals (Au, Cu and Ag) are state-of-the-art electrocatalysts for the CO2 reduction reaction (CO2RR). Size-dependent CO2RR activity of Au and Cu has been studied, and increased H2 evolution reaction (HER) activity is expected for small catalyst particles with high population of undercoordinated corner sites. A similar consensus is still lacking for Ag catalysts because the ligands and stabilizers typically used to control particle synthesis can block specific active sites and mask inherent structure-property trends. This knowledge gap is problematic because increased performance and catalyst utilization are still needed to improve economic viability. We combined density functional theory, microkinetic modeling, and experiment to demonstrate a strong size-dependence for pristine Ag particles in the sub-10 nm range. Small diameter particles with a high population of Ag edge sites were predicted to favor HER, whereas CO2RR selectivity increased towards that of bulk Ag for larger diameter particles as the population of Ag(100) surface sites grew. Experimental results validated these predictions and we identified an optimal particle diameter of 8-10 nm that balanced selectivity and activity. Particles below this diameter suffered from poor selectivity, while larger particles demonstrated bulk-like activity and reduced catalyst utilization. These results demonstrate the size-dependent CO2RR activity of pristine Ag catalysts and will help guide future development efforts.

scholarly journals Identification of different oxygen species in oxide nanostructures with 17O solid-state NMR spectroscopy

2015 ◽  
Vol 1 (1) ◽  
pp. e1400133 ◽  
Author(s):  
Meng Wang ◽  
Xin-Ping Wu ◽  
Sujuan Zheng ◽  
Li Zhao ◽  
Lei Li ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Strong Dependence ◽  
Critical Role ◽  
Oxygen Species ◽  
Structure Property ◽  
Diverse Range ◽  
Oxygen Ions ◽  
Surface Sites ◽  
Nanostructured Oxides

Nanostructured oxides find multiple uses in a diverse range of applications including catalysis, energy storage, and environmental management, their higher surface areas, and, in some cases, electronic properties resulting in different physical properties from their bulk counterparts. Developing structure-property relations for these materials requires a determination of surface and subsurface structure. Although microscopy plays a critical role owing to the fact that the volumes sampled by such techniques may not be representative of the whole sample, complementary characterization methods are urgently required. We develop a simple nuclear magnetic resonance (NMR) strategy to detect the first few layers of a nanomaterial, demonstrating the approach with technologically relevant ceria nanoparticles. We show that the 17O resonances arising from the first to third surface layer oxygen ions, hydroxyl sites, and oxygen species near vacancies can be distinguished from the oxygen ions in the bulk, with higher-frequency 17O chemical shifts being observed for the lower coordinated surface sites. H217O can be used to selectively enrich surface sites, allowing only these particular active sites to be monitored in a chemical process. 17O NMR spectra of thermally treated nanosized ceria clearly show how different oxygen species interconvert at elevated temperature. Density functional theory calculations confirm the assignments and reveal a strong dependence of chemical shift on the nature of the surface. These results open up new strategies for characterizing nanostructured oxides and their applications.

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 Theoretical Investigation on Structure-Property Relationship of Asymmetric Clusters (CH3FBN3)n (n = 1– 6)

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Deng-Xue Ma ◽  
Yao-Yao Wei ◽  
Yun-Zhi Li ◽  
Guo-Kui Liu ◽  
Qi-Ying Xia
Keyword(s):  
Thermodynamic Properties ◽  
Density Functional ◽  
Dft Method ◽  
Energy Difference ◽  
Structure Property ◽  
Functional Theory ◽  
Size Dependent ◽  
Stable Clusters ◽  
Chemical Inertness ◽  
Relationship Of

The structural, relative stability, electronic, IR vibrational, and thermodynamic properties of asymmetric clusters (CH3FBN3)n (n = 1–6) are systematically investigated using density functional theory (DFT) method. Results show that clusters (CH3FBN3)n (n = 2–6) form a cyclic structure with a B atom and a Nα atom binding together. Five main characteristic regions are observed and assigned for the calculated IR spectra. The size-dependent second-order energy difference shows that clusters (CH3FBN3)3 and (CH3FBN3)5 have relatively higher stability and enhanced chemical inertness compared with the neighboring clusters. These two clusters may serve as the cluster-assembled materials. The variations of thermodynamic properties with temperature T or cluster size n are analyzed, respectively. Based on enthalpies in the range of 200–800 K, the formations of the most stable clusters (CH3FBN3)n (n = 2–6) from monomer are thermodynamically favorable. These data are helpful to design and synthesize other asymmetric boron azides.

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 Active sites for tandem reactions of CO2 reduction and ethane dehydrogenation

2018 ◽  
Vol 115 (33) ◽  
pp. 8278-8283 ◽  
Author(s):  
Binhang Yan ◽  
Siyu Yao ◽  
Shyam Kattel ◽  
Qiyuan Wu ◽  
Zhenhua Xie ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Raw Materials ◽  
Co2 Reduction ◽  
Tandem Reactions ◽  
In Situ Characterization ◽  
Functional Theory ◽  
Ethane Dehydrogenation ◽  
Ethylene Selectivity

Ethylene (C2H4) is one of the most important raw materials for chemical industry. The tandem reactions of CO2-assisted dehydrogenation of ethane (C2H6) to ethylene creates an opportunity to effectively use the underutilized ethane from shale gas while mitigating anthropogenic CO2 emissions. Here we identify the most likely active sites over CeO2-supported NiFe catalysts by using combined in situ characterization with density-functional theory (DFT) calculations. The experimental and theoretical results reveal that the Ni–FeOx interfacial sites can selectively break the C–H bonds and preserve the C–C bond of C2H6 to produce ethylene, while the Ni–CeOx interfacial sites efficiently cleave all of the C–H and C–C bonds to produce synthesis gas. Controlled synthesis of the two distinct active sites enables rational enhancement of the ethylene selectivity for the CO2-assisted dehydrogenation of ethane.

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.

scholarly journals Steering elementary steps towards efficient alkaline hydrogen evolution via size-dependent Ni/NiO nanoscale heterosurfaces

2019 ◽  
Vol 7 (1) ◽  
pp. 27-36 ◽  
Author(s):  
Lu Zhao ◽  
Yun Zhang ◽  
Zhonglong Zhao ◽  
Qing-Hua Zhang ◽  
Lin-Bo Huang ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Active Sites ◽  
Density Functional ◽  
Surface Composition ◽  
Underlying Mechanism ◽  
Water Dissociation ◽  
Elementary Steps ◽  
Size Dependent ◽  
Extra Energy ◽  
Nio Nanocrystals

Abstract Alkaline hydrogen evolution reaction (HER), consisting of Volmer and Heyrovsky/Tafel steps, requires extra energy for water dissociation, leading to more sluggish kinetics than acidic HER. Despite the advances in electrocatalysts, how to combine active sites to synergistically promote both steps and understand the underlying mechanism remain largely unexplored. Here, Density Functional Theory (DFT) calculations predict that NiO accelerates the Volmer step while metallic Ni facilitates the Heyrovsky/Tafel step. A facile strategy is thus developed to control Ni/NiO heterosurfaces in uniform and well-dispersed Ni-based nanocrystals, targeting both reaction steps synergistically. By systematically modulating the surface composition, we find that steering the elementary steps through tuning the Ni/NiO ratio can significantly enhance alkaline HER activity, and Ni/NiO nanocrystals with a Ni/NiO ratio of 23.7% deliver the best activity, outperforming other state-of-the-art analogues. The results suggest that integrating bicomponent active sites for elementary steps is effective for promoting alkaline HER, but they have to be balanced.

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.

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>

Towards a Design of Active Oxygen Evolution Catalysts: Insights from Automated Density Functional Theory Calculations and Machine Learning

2019 ◽  
Author(s):  
Seoin Back ◽  
Kevin Tran ◽  
Zachary Ulissi
Keyword(s):  
Machine Learning ◽  
Oxygen Evolution ◽  
Active Sites ◽  
Density Functional ◽  
Chemical Space ◽  
Density Functional Theory Calculations ◽  
Catalyst Design ◽  
Transition Metal Catalysts ◽  
Oxide Materials ◽  
Design Strategies

<div> <div> <div> <div><p>Developing active and stable oxygen evolution catalysts is a key to enabling various future energy technologies and the state-of-the-art catalyst is Ir-containing oxide materials. Understanding oxygen chemistry on oxide materials is significantly more complicated than studying transition metal catalysts for two reasons: the most stable surface coverage under reaction conditions is extremely important but difficult to understand without many detailed calculations, and there are many possible active sites and configurations on O* or OH* covered surfaces. We have developed an automated and high-throughput approach to solve this problem and predict OER overpotentials for arbitrary oxide surfaces. We demonstrate this for a number of previously-unstudied IrO2 and IrO3 polymorphs and their facets. We discovered that low index surfaces of IrO2 other than rutile (110) are more active than the most stable rutile (110), and we identified promising active sites of IrO2 and IrO3 that outperform rutile (110) by 0.2 V in theoretical overpotential. Based on findings from DFT calculations, we pro- vide catalyst design strategies to improve catalytic activity of Ir based catalysts and demonstrate a machine learning model capable of predicting surface coverages and site activity. This work highlights the importance of investigating unexplored chemical space to design promising catalysts.<br></p></div></div></div></div><div><div><div> </div> </div> </div>

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