Abstract
The reactivity of the same molecular electrocatalyst under homogenous 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 CO2 binding 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 at the interface, which in turn stabilises the bound CO2. Furthermore, controlled computational experiments suggest that neither the electric field nor the cations alone can produce significant stabilisation, but that the combination led to a dramatic stabilisation of the CO2 bound state.
Highlights
It is well known that homogeneous catalysts offer the possibility of molecular engineering, making high activity and selectivity[1−3] possible
We found that the catalyst−nanotube interaction was important: a stronger tendency for aggregation was found for smaller nanotubes due to the better catalyst−catalyst π−π interactions as compared to the catalyst−smaller carbon nanotubes (CNTs) interactions
We present an EVB study of the CO2 binding process for a Co(TPP)−CNT system at the once reduced state, which serves as an example to understand the roles that the beforementioned three factors played in reactions at the interfaces
Summary
It is well known that homogeneous catalysts offer the possibility of molecular engineering, making high activity and selectivity[1−3] possible. Carbon materials with large surface areas, such as carbon nanotubes (CNTs),[6] graphene,[7] and even carbon black,[8] act as good supporting materials for molecular catalysts, enabling them to function in reaction media such as water, which is otherwise impossible Due to their high electrical conductivity, such catalyst/support combination has been found to create excellent electrocatalytic materials.[9,10] The easiest strategy for immobilization is physical adsorption, which relies on the π−π contact and/or electrostatic interactions between the catalyst and the electrode, either with or without an extra supporting material.[11] Several studies[6,12,13] demonstrate the same trend; when the catalysts are immobilized on a carbon supporting material,[14] such as CNTs or a graphene nanofiber, and react in a heterogeneous fashion, their performances, in terms of turnover frequency (TOF), increased dramatically. It was reported in 2017 that adhering Co(TPP)
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