| 1. |
- Chen, Xiaoyu, et al.
(författare)
-
Deconstructing the Enhancing Effect on CO2 Activation in the Electric Double Layer with EVB Dynamic Reaction Modeling
- 2020
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:41, s. 22479-22487
-
Tidskriftsartikel (refereegranskat)abstract
- The reactivities of the same molecular electrocatalyst under homogeneous and heterogeneous conditions can be dramatically different, highlighting that the reaction environment plays an important role in catalysis. For catalysis on solid electrodes, reactions take place in the electric double layer (EDL), where a strong electric field is experienced. In this work, empirical valence bond molecular dynamics (EVB-MD) was used to explore CO2binding in the EDL. It allows explicit descriptions of the solvent, electrolyte, catalyst–reactant, and the electrode surface material, as well as an unbiased description of the applied electric field. The strong local electric field concentrates cations, which in turn stabilizes the bound CO2. Furthermore, controlled computational experiments suggest that neither the electric field nor the cations alone can produce significant stabilization, but that the combination leads to a dramatic stabilization of the CO2 bound state.
|
|
| 2. |
- Chen, Xiaoyu, 1993-
(författare)
-
Theoretical Studies on CO2 Reduction Electrocatalysts
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The atmospheric CO2 concentration has increased by more than 20% since 1980s and has now reached the highest level than at any point in the past 800 000 years. Electrochemical CO2 reductions are receiving particular in- terest as the apparatus are relatively easy to maintain and cheap to operate. However, the direct reduction of CO2 into CO2 radical requires a very high over-potential, meaning a substantial waste in energy. In order to lower the over-potential required, a large number of catalysts has been synthesised and studied. Among these catalysts, three are studied in this work due to their interesting reactivities. We believe the further understanding gained in our studies will benefit the development of new and better catalysts.Ru(6-Mebpy)(tBu3-tpy) reduces CO2 at its first reduction potential and can therefore lower the over-potential required significantly. This observation is unique for Ru(tpy)(bpy) type of catalysts. Density functional theory (DFT) cal- culations revealed that the steric hindrance provided by the 6-methyl group weakens Ru-solvent interactions and hence allows solvent detachment to take place after only one reduction, which is otherwise not possible. Furthermore, we proposed a new mechanism for CO2 to CO reduction at the first reduc- tion potential and identified a cyclic intermediate by Infra-red spectroscopy in collaboration with experimentalists. Such intermediate was not reported pre- viously for Ru-based electrocatalysts.Co(TPP)/CNTs as a heterogenous catalyst exhibits superior reactivity as compared to in solution. DFT calculations with implicit solvent model ac- counts its enhanced reactivity to the increased proton concentration in water. The inverse-loading effect was studied by potential mean force (PME) sam- pling. Our results suggest that aggregation is triggered by the strong inter- molecular p - p interactions among the catalysts. Flatter nanotubes have better contact with Co(TPP) and hence reduces aggregation tendency. The same cat- alyst was also used as an example to study catalysis at interfaces in an electric field. Our full-explicit EVB -MD (Empirical Valence Bond-Molecular Dynam- ics) model illustrates that the electric double layer concentrates cations, which significantly stabilises polarised CO2 at a higher concentration and hence eases CO2 binding. Furthermore, we have also shown that either the electric field or the cations along provides only a minor, almost negligible stabilisation.In 2019, CoPc/CNTs was reported to be the first early-period transition metal complex that can catalyse CO2-to-CH3OH conversion at a decent yield. Literature search on previous work suggests that the presence of well-dispersed, monomeric CoPc is crucial to further reduce CO into CH3OH. We calculated the reaction profiles for both monomeric CoPc and dimeric CoPc, which is the simplest form of aggregates. Our DFT results demonstrate that after the formation of catalyst-CO- complex, monomers tend to go though further reac- tions to afford CH3OH while dimers tend to dissociate CO as reductions are slightly harder, which in turn, is raised from a less degree of solvation stabili- sation upon reductions.
|
|
| 3. |
- Chen, Xiaoyu, et al.
(författare)
-
Understanding the Enhanced Catalytic CO2 Reduction upon Adhering Cobalt Porphyrin to Carbon Nanotubes and the Inverse Loading Effect
- 2020
-
Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 39:9, s. 1634-1641
-
Tidskriftsartikel (refereegranskat)abstract
- Adhering a cobalt porphyrin (Co(TPP)) catalyst on a carbon nanotube (CNT) supporting material greatly enhances its reactivity and enables catalysis in water, which is otherwise impossible. However, the effect of solvent as well as supporting materials on catalysis is still elusive. On the basis of computational results we found that water as a reaction medium lowers the reductive potential required due to the stabilization of intermediates and transition states, and provides higher availability of protons. To understand the effect of the support materials, we combine computations and experiments and illustrate that the curvature of the nanotubes plays an essential role in aggregation through the competition between the Ï-πinteractions between the porphyrin rings as well as between the Co(TPP) and the nanotube, providing an insight into lessening the degree of aggregation.
|
|
| 4. |
- Guo, Yaxiao, et al.
(författare)
-
Molybdenum and boron synergistically boosting efficient electrochemical nitrogen fixation
- 2020
-
Ingår i: Nano Energy. - : Elsevier Ltd. - 2211-2855 .- 2211-3282. ; 78
-
Tidskriftsartikel (refereegranskat)abstract
- Ammonia production consumes ~2% of the annual worldwide energy supply, therefore strategic alternatives for the energy-intensive ammonia synthesis through the Haber-Bosch process are of great importance to reduce our carbon footprint. Inspired by MoFe-nitrogenase and the energy-efficient and industrially feasible electrocatalytic synthesis of ammonia, we herein establish a catalytic electrode for artificial nitrogen fixation, featuring a carbon fiber cloth fully grafted by boron-doped molybdenum disulfide (B-MoS2/CFC) nanosheets. An excellent ammonia production rate of 44.09 μg h–1 cm–2 is obtained at −0.2 V versus the reversible hydrogen electrode (RHE), whilst maintaining one of the best reported Faradaic efficiency (FE) of 21.72% in acidic aqueous electrolyte (0.1 M HCl). Further applying a more negative potential of −0.25 V renders the best ammonia production rate of 50.51 μg h–1 cm–2. A strong-weak electron polarization (SWEP) pair from the different electron accepting and back-donating capacities of boron and molybdenum (2p shell for boron and 5d shell for molybdenum) is proposed to facilitate greatly the adsorption of non-polar dinitrogen gas via N≡N bond polarization and the first protonation with large driving force. In addition, for the first time a visible light driven photo-electrochemical (PEC) cell for overall production of ammonia, hydrogen and oxygen from water + nitrogen, is demonstrated by coupling a bismuth vanadate BiVO4 photo-anode with the B-MoS2/CFC catalytic cathode.
|
|
| 5. |
- Juan Angel, de Gracia Triviño, 1989-, et al.
(författare)
-
Oxide Relay: An Efficient Mechanism for Catalytic Water Oxidation at Hydrophobic Electrode Surfaces
- 2020
-
Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:17, s. 7383-7387
-
Tidskriftsartikel (refereegranskat)abstract
- In order to combine the advantages of molecular catalysts with the stability of solid-state catalysts, hybrid systems with catalysts immobilized on carbon nanotubes are prominent candidates. Here we explore our recent mechanistic proposal for Ru(tda)(py)2, the oxide relay mechanism, in a hybrid system from an experimental study. It reacts with the same efficiency but with increased stability compared to the homogeneous molecular catalyst. We used the empirical valence bond method and molecular dynamics with enhanced sampling approaches to investigate the two key steps in the mechanism: the intramolecular O–O bond formation and the OH– nucleophilic attack. The results on these calculations show that the oxide relay mechanism remains unaltered in the new environment. We believe that the principles should apply to other oxide containing dangling groups and to other metal centers, opening new possibilities of future developments on hybrid molecular catalyst-based water splitting devices.
|
|
| 6. |
- Li, Ge, et al.
(författare)
-
Utilizing the Surface Electrostatic Potential to Predict the Interactions of Pt and Ni Nanoparticles with Lewis Acids and Bases-sigma-Lumps and sigma-Holes Govern the Catalytic Activities
- 2020
-
Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:27, s. 14696-14705
-
Tidskriftsartikel (refereegranskat)abstract
- An improved understanding of the interactions of transition-metal (TM) nanoparticles with Lewis acids/bases will facilitate the design of more efficient catalysts. Therefore, Pt-14, Pt-13, Pt-12, and Ni-12 nanoparticles have been studied at the TPSSh/Def2-TZVP level of density functional theory (DFT). Surface electrostatic potential [V-S(r)] maps are used to analyze the Lewis acidic and basic properties of all nanoparticles and indicate that the interactions of Pt and Ni nanoparticles are governed by sigma(d)-holes and sigma(s) -holes, respectively. Lewis acids (Na+, HF) and a Lewis base (H2O) have been tested as ligands to probe the local interaction proficiencies. The comparison between binding energies and V-S(r) shows that the lowest minimum (V-S,V-min) and highest maximum (V-S,V-max) of V-S(r) on each particle can predict the most favorable binding site for the Lewis acids and base, respectively. V(S,min )can also rank the different binding strengths of Na+ and HF with the nanoparticles. For H2O, the binding strength versus V-S,V-max correlation is better for Ni-12 than for the Pt nanoparticles. This observation is discussed in relation to charge transfer/polarization and structural deformation upon interaction. In light of our findings, we compare the catalytic potential of Ni to the less abundant but more commonly used Pt.
|
|
| 7. |
- Nie, Wan, et al.
(författare)
-
Mechanistic study on the regioselective Ni-catalyzed dicarboxylation of 1,3-dienes with CO2
- 2020
-
Ingår i: ORGANIC CHEMISTRY FRONTIERS. - : Royal Society of Chemistry (RSC). - 2052-4129. ; 7:24, s. 4080-4088
-
Tidskriftsartikel (refereegranskat)abstract
- Ni-Catalyzed dicarboxylation of 1,3-dienes with CO2 provides a regioselective method for the construction of adipic acids. Here, density functional theory (DFT) calculations have been carried out to elucidate the detailed mechanisms of this reaction and the origin of regioselectivity. The computed results reveal that the catalytic cycle mainly proceeds via Ni(0)-catalyzed 1(st) carboxylation, followed by a reduction of the Ni(ii) to Ni(i) intermediate and finally a Ni(i)-catalyzed 2(nd) carboxylation. The first and second carboxylations are rate- and regioselectivity-determining steps, respectively. In the first carboxylation, a new activation mode of CO2 by insertion into the uncoordinated alkene group has been found to be optimal. This is in contrast to other mechanisms described in the literature. Furthermore, we found that the interaction between the allyl group and nickel center in the alkyl Ni(i) intermediate significantly stabilizes the d(9) electron configuration. This stabilizing interaction results in the preferential 1,4-dicarboxylation.
|
|
| 8. |
- Zhan, Shaoqi, et al.
(författare)
-
Hydrophobic/Hydrophilic Directionality Affects the Mechanism of Ru-Catalyzed Water Oxidation Reaction
- 2020
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 10:22, s. 13364-13370
-
Tidskriftsartikel (refereegranskat)abstract
- From the study of supramolecular dimers of [(RuO)-O-V(pda)](+) (pda = 1,10-phenanthroline-2,9-dicarboxylic acid) and [(RuO)-O-V(bda)](+) (bda = 2,2'-bipyridine-6,6'-dicarboxylate) complexes, the O-O bond-forming intermediates in water oxidation, we found orientational distinction induced by the pda and bda ligands. The bda complex prefers the front-to-front geometry, while the pda complex favors the front-to-back geometry in the formation of prereactive geometry. In the bda complex, the hydrophobic oxo will point at another oxo with the bda directed toward water, which favors the I2M mechanism. In the pda complex, the hydrophobic oxo instead is directed toward a more hydrophobic phenanthroline moiety of the pda of another species, which disfavors I2M. The binding free energy of the nonproductive front-to-back of pda is 3 kcal mol(-1) more stable than that of the prereactive dimer. This incorrect orientation leads to an additional rearrangement required before the O-O bond can be formed. Estimation of the rate constant shows 2 orders of magnitude lower reactivity for the I2M mechanism of the pda complex relative to the bda complex, which makes the water nucleophilic attack mechanism competitive.
|
|
