Electrochemical interfacial influences on deoxygenation and hydrogenation reactions in CO reduction on a Cu(100) surface.

Electroreduction of CO2 to hydrocarbons on a copper surface has attracted much attention in the last few decades for providing a sustainable way for energy storage. During the CO2 and further CO electroreduction processes, deoxygenation that is C-O bond dissociation, and hydrogenation that is C-H bond formation, are two main types of surface reactions catalyzed by the copper electrode. In this work, by performing the state-of-the-art constrained ab initio molecular dynamics simulations, we have systematically investigated deoxygenation and hydrogenation reactions involving two important intermediates, COHads and CHOads, under various conditions of (i) on a Cu(100) surface without water molecules, (ii) at the water/Cu(100) interface and (iii) at the charged water/Cu(100) interface, in order to elucidate the electrochemical interfacial influences. It has been found that the electrochemical interface can facilitate considerably the C-O bond dissociation via changing the reaction mechanisms. However, C-H bond formation has not been affected by the presence of water or electrical charge. Furthermore, the promotional roles of an aqueous environment and negative electrode potential in deoxygenation have been clarified, respectively. This fundamental study provides an atomic level insight into the significance of the electrochemical interface towards electrocatalysis, which is of general importance for understanding electrochemistry

Elucidation of the surface structure-selectivity relationship in ethanol electro-oxidation over platinum by density functional theory

We have successfully built a general framework to comprehend the structure-selectivity relationship in ethanol electrooxidation on platinum by density functional theory calculations. Based on the reaction mechanisms on three basal planes and five stepped surfaces, it was found that only (110) and n(111) × (110) sites can enhance CO2 selectivity but other non-selective step sites are more beneficial to activity

New insights into electrocatalytic ozone generation via splitting of water over PbO2 electrode: A DFT study

© 2016 Elsevier B.V. All rights reserved. The viable mechanisms for O3 generation via the electrocatalytic splitting of H2O over β-PbO2 catalyst were identified through Density Functional Theory calculations. H2O adsorbed onto the surface was oxidized to form OH then O; the latter reacted with a surface bridging O to form O2 which in turn reacted with another surface O to form O3. The final step of the mechanisms occurs via an Eley-Rideal style interaction where surface O2 desorbs and then attacks the surface bridging oxygen, forming O3. A different reaction pathway via an O3H intermediate was found less favoured both thermodynamically and kinetically

Insights into the mechanism of electrochemical ozone production via water splitting on the Ni and Sb Doped SnO2 catalyst

The H2O splitting mechanism is a very attractive alternative used in electrochemistry for the formation of O3. The most efficient catalysts employed for this reaction at room temperature are SnO2-based, in particular the Ni/Sb-SnO2 catalyst. In order to investigate the H2O splitting mechanism Density Functional Theory (DFT) was performed on a Ni/Sb-SnO2 surface with oxygen vacancies. By calculating different SnO2 facets, the (110) facet was deemed most stable, and further doped with Sb and Ni. On this surface, the H2O splitting mechanism was modelled paying particular attention to the final two steps, the formation of O2 and O3. Previous studies on β-PbO2 have shown that the final step in the reaction (the formation of O3) occurs via an Eley-Rideal style interaction where surface O2 desorbs before attacking surface O to form O3. It is revealed that for Ni/Sb-SnO2, although the overall reaction is the same the surface mechanism is different. The formation of O3 is found to occur through a Langmuir-Hinshelwood mechanism as opposed to Eley-Rideal. In addition to this the relevant adsorption energies (Eads), Gibb’s free energy (ΔGrxn) and activation barriers (Eact) for the final two steps modelled in the gas phase have been shown; providing the basis for a tool to develop new materials with higher current efficiencies

An insight into methanol oxidation mechanisms on RuO2(100) under an aqueous environment by DFT calculations

In this work, we have studied methanol oxidation mechanisms on RuO2(100) by using density functional theory (DFT) calculations and ab initio molecular dynamics (MD) simulations with some explicit interfacial water molecules. The overall mechanisms are identified as: CH3OH* → CH3O* → HCHO* → HCH(OH)2* → HCHOOH* → HCOOH* → mono-HCOO* → CO2*, without CO formation. This study provides a theoretical insight into C1 molecule oxidation mechanisms at atomic levels on metal oxide surfaces under an aqueous environment

Supplementary information files for A strategy for CO₂ capture and utilization towards methanol production at industrial scale: an integrated highly efficient process based on multi-criteria assessment

© the Authors CC-BY 4.0Supplementary files for article A strategy for CO2 capture and utilization towards methanol production at industrial scale: an integrated highly efficient process based on multi-criteria assessmentCO2 capture and utilization are an effective solution to the problem of CO2 emissions, and a combination of ammonia-based CO2 capture and its use for methanol production is a highly feasible strategy. However, the uses of conventional technologies have resulted in a high demand for energy, with limited use of hydrogen. To address these problems, an innovative strategy is proposed and demonstrated in this study that enhances the conventional design, i.e., to use ammonia-based CO2 capture with double tower absorption and solvent split, along with wet hydrogen for methanol production at industrial scale. The process is further improved through a multi-criteria assessment that considered the CO2 capture rate, NH3 loss rate, CO2 conversion rate, and energy saving factors, in which the latter is based on two components, namely the reboiler duty and the condenser duty. Moreover, an exergy analysis method is used to optimize the improved process, and a highly efficient integrated process is finally established. It has been found that the use of a double-tower absorption process ensures high rates of CO2 capture and low rates of NH3 loss. Additionally, adjusting the molar ratio of H2 to CO2 leads to an impressive 8% increase in the CO2 conversion rate, reaching 25%. In terms of energy savings, the average reboiler duty was reduced from 13.39 to 11.85 MJ/kgCO2, i.e., by 11.50%; while the condenser duty was reduced by 11.36%; both contributed to the overall energy savings. In the I-ACCMP process, the total exergy loss is 437.24 kW, of which the exergy loss of the heat exchangers accounts for 16%, and the desorption tower (DES) accounts for 48%. After optimization, the exergy loss of the heat exchangers decreases from 70.02 kW to 40.45 kW, the exergy loss of the DES decreases from 209.29 kW to 180.91 kW, and the reboiler duty is reduced from 10.60 MJ/kgCO2 to 7.71 MJ/kgCO2. The total exergy loss decreases from 437.24 kW to 372.68 kW, which is a reduction by 14.8%.</p

Insight into CO activation over Cu(100) under electrochemical conditions

The reduction of CO2 on copper electrodes has attracted great attentions in the last decades, since it provides a sustainable approach for energy restore. During the CO2 reduction process, the electron transfer to COads is experimentally suggested to be the crucial step. In this work, we examine two possible pathways in CO activation, i.e. to generate COHads and CHOads, respectively, by performing the state-of-the-art constrained ab initio molecular dynamics simulations on the charged Cu(100) electrode under aqueous conditions, which is close to the realistic electrochemical condition. The free energy profile in the formation of COHads via the coupled proton and electron transfer is plotted. Furthermore, by Bader charge analyses, a linear relationship between C-O bond distance and the negative charge in CO fragment is unveiled. The formation of CHOads is identified to be a surface catalytic reaction, which requires the adsorption of H atom on the surface first. By comparing these two pathways, we demonstrate that kinetically the formation of COHads is more favored than that of CHOads, while CHOads is thermodynamically more stable. This work reveals that CO activation via COHads intermediate is an important pathway in electrocatalysis, which could provide some insights into CO2 electroreduction over Cu electrodes

Electrocatalytic oxidation of ethanol and ethylene glycol on cubic, octahedral and rhombic dodecahedral palladium nanocrystals

Cubic, octahedral and rhombic dodecahedral Pd nanocrystals were synthesized and examined as nanocatalysts for electro-oxidation of ethanol and ethylene glycol. Combined electrochemical measurements and density functional theory calculations reveal that nanofacet-dependent affinity and reactivity of OHads and COads are closely linked to the C2 alcohol oxidation activities, with the highest reactivity found on the Pd nanocubes bounded by {100} facets

Effect of mass transport on the electrochemical oxidation of alcohols over electrodeposited film and carbon-supported pt electrodes

© 2018 The Author(s) Electrochemical oxidation of four different alcohol molecules (methanol, ethanol, n-butanol and 2-butanol) at electrodeposited Pt film and carbon-supported Pt catalyst film electrodes, as well as the effect of mass transport on the oxidation reaction, has been studied systematically using the rotating disk electrode (RDE) technique. It was shown that oxidation current decreased with an increase in the rotation rate (ω) for all alcohols studied over electrodeposited Pt film electrodes. In contrast, the oxidation current was found to increase with an increase in the ω for Pt/C in ethanol and n-butanol-containing solutions. The decrease was found to be nearly reversible for ethanol and n-butanol at the electrodeposited Pt film electrode ruling out the possibility of intermediate CO ads poisoning being the sole cause of the decrease and was attributed to the formation of soluble intermediate species which diffuse away from the electrode at higher ω. In contrast, an increase in the current with an increase in ω for the carbon supported catalyst may suggest that the increase in residence time of the soluble species within the catalyst layer, results in further oxidation of these species. Furthermore, the reversibility of the peak current on decreasing the ω could indicate that the surface state has not significantly changed due to the sluggish reaction kinetics of ethanol and n-butanol

Designing Pt-based electrocatalysts with high surface energy

The reactivity of an electrocatalyst depends strongly on its surface structure. Pt-based electrocatalysts of nanocrystals (NCs) enclosed with high-index facets contain a large density of catalytically active sites formed from step and kink atoms on the facets and exhibit intrinsically superior activity. However, the Pt-based NCs of high-index facets do possess a high surface energy and are thermodynamically metastable, leading to a big challenge in their shape-controlled synthesis. To overcome the challenge, kinetic–thermodynamic control of crystal growth is indispensable and is currently realized mainly by electrochemical methods and surfactant-based wet chemical approaches. This Perspective reviews recent progresses in Pt-based electrocatalysts of monometallic and bimetallic NCs of high surface energy with different morphologies of convex or concave tetrahexahedron, trapezohedron, trisoctahedron, hexoctahedron, etc. Remarkable electrocatalytic performance of these NCs has been demonstrated. Despite the considerable progress already made, the electrocatalysts of NCs with high surface energy still hold significant future opportunities in both fundamental understanding and practical applications