Investigation of the Initial Steps of the Electrochemical Reduction of CO₂ on Pt Electrodes

Abstract

The initial steps of the electrochemical reduction of CO2 at Pt electrodes were computationally investigated at the molecular level. Simulations were performed with density functional theory using the B3LYP functional and effective core potential basis sets. The surface was modeled through two clusters comprising 13 and 20 atoms. An implicit solvation model was used to describe solvation effects for two different solvents: water and acetonitrile. It was found that CO2 adsorption is highly favored on negatively charged clusters and takes place passing from a well-defined transition state. The computational evidence suggests that the electrodic CO2 adsorption reaction may be described as a concerted process in which an electron-transfer reaction takes place contextually to CO2 adsorption. Also, the present results suggest that the formation of the CO2(•–) aqueous species is significantly unfavored from an energetic standpoint and that its main fate, if formed, would be most likely that of getting adsorbed again on the Pt surface. The calculation of the pKa of adsorbed CO2(–) showed that its protonation reaction is thermodynamically favored in most electrochemical conditions used for CO2 reduction. Also, it was found that the free-energy difference between adsorbed formate and adsorbed COOH favors the latter, suggesting that the interconversion kinetics of these two species at a Pt surface may play an important role in determining the system reactivity. A tentative global mechanism able to describe the CO2 reactivity on Pt surfaces is proposed.

Evaluating Solvent Effects at the Aqueous/Pt(111) Interface

“…In the literature, properties such as adsorption and reaction energies in the gas phase have often been used to assess cluster‐size effects . However, a relatively limited amount of work is available on understanding the effect of cluster size on surface processes in the presence of implicit solvation. We first sought to determine which Pt cluster would be appropriate for this work.…”

CO2 hydrogenation on Pt, Pt/SiO2 and Pt/TiO2: Importance of synergy between Pt and oxide support

“…Indeed, the *HOCO intermediate has also been predicted to be formed on Pt-based catalysts for CO 2 hydrogenation according to the previous theoretical studies. [43,44] In addition, for the sequential reactions along the RWGS + CO-Hydro pathways the highest E a is 1.29 eV for *CO hydrogenation, much lower than that along the formate pathways via *HCOO (1.80 eV for the *HCOOH hydrogenation). Such big difference in the highest E a suggests that CO 2 hydrogenation is likely to prefer the RWGS + CO-hydro pathways rather than the format pathways on the Pt NP.…”

“…It has displayed its potential applications as a catalyst for reforming reactions such as reforming of ethanol (C 2 H 5 OH) [27,28] and n-Hexane [29], the water-gas-shift (WGS) reaction at low temperature [30][31][32], the direct oxidation of CH 4 to syngas [33][34][35][36][37], and CO oxidation. [38][39][40][41] CO 2 activation by H 2 undergoes the RWGS reaction on Pt(111) and leads to the production of CO via the *HOCO intermediate [42][43][44], while the produced CO can be further hydrogenated to CH 4 via C-O bond cleavage. [43] However, in practice Pt catalysts are in the form of nanoparticles (NPs) supported primarily on oxides, which can behave differently from Pt(111).…”

Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide

“…In fact, besides the aforementioned Au, Ag, and Cu electrodes, some other metals like Sn, Pd, Bi, Pb, In, and Pt have also been investigated as potential electrocatalysts for CO 2 conversion. To have a better understanding of these metal catalysts, several of them, such as Sn, Pd, and Bi, are presented here.…”