Electrocatalytic CO₂ Reduction: Monitoring of Catalytically Active, Downgraded, and Upgraded Cobalt Complexes

Abstract

The premise of most studies on the homogeneous electrocatalytic CO 2 reduction reaction (CO 2 RR) is a good understanding of the reaction mechanisms. Yet, analyzing the reaction intermediates formed at the working electrode is challenging and not always attainable. Here, we present a new, general approach to studying the reaction intermediates applied for CO 2 RR catalyzed by a series of cobalt complexes. The cobalt complexes were based on the TPA-ligands (TPA = tris(2pyridylmethyl)amine) modified by amino groups in the secondary coordination sphere. By combining the electrochemical experiments, electrochemistry-coupled electrospray ionization mass spectrometry, with density functional theory (DFT) calculations, we identify and spectroscopically characterize the key reaction intermediates in the CO 2 RR and the competing hydrogen-evolution reaction (HER). Additionally, the experiments revealed the rarely reported in situ changes in the secondary coordination sphere of the cobalt complexes by the CO 2 -initiated transformation of the amino substituents to carbamates. This launched an even faster alternative HER pathway. The interplay of three catalytic cycles, as derived from the experiments and supported by the DFT calculations, explains the trends that cobalt complexes exhibit during the CO 2 RR and HER. Additionally, this study demonstrates the need for a molecular perspective in the electrocatalytic activation of small molecules efficiently obtained by the EC-ESI-MS technique.

Synthesis, Characterization, and Reactivity of a Synthetic End-On Cobalt(II) Alkyl Persulfide Complex as a Model Platform for Thiolate Persulfidation

“…Upon electrochemical reduction, we did not observe any notable reduction features in the cyclic voltammogram of 1 , suggesting that reduction of free RSS – to S 2– and RS – occurs at highly reducing and inaccessible potentials (Figure S35). The RSS – reduction, however, does appear to be accessible once coordinated to Co 2+ based on the two irreversible reduction features emerged in the cyclic voltammogram for 2 at −1420 and −1630 mV vs SCE, which are assigned as RSS – and Co 2+ → Co 1+ reduction events, respectively, after surveying known Co 2+ → Co 1+ reduction potentials for a number of Co 2+ TPA complexes with less donating halide ligands. − We anticipate that 2 with a more donating RSS – ligand would possess a more negative reduction potential than that of [Co II (TPA)(Cl)] + (−1540 mV vs SCE) for the Co 2+ → Co 1+ event.…”

Intricacies of Mass Transport during Electrocatalysis: A Journey through Iron Porphyrin-Catalyzed Oxygen Reduction

“…Insights into catalyst degradation pathways during these processes have been notably elusive. Understanding these degradation mechanisms is vital for developing more robust and efficient electrocatalytic systems. − …”

Constructing a Stable Built-In Electric Field in Bi/Bi2Te3 Nanowires for Electrochemical CO2 Reduction Reaction

“…It is well known that after CO 2 molecules are adsorbed on the surface of the catalyst, the O atom therein combines with the catalytic site through proton-coupled steps and then transform into *OCHO and *COOH, which are important intermediates for the generation of HCOOH and CO, respectively. − At present, however, the research of CO 2 RR electrocatalysts primarily focuses on facet control, defect engineering, and composition regulation, with limited exploration of key reaction intermediates . Therefore, achieving precise control of reaction intermediates to efficiently convert target products in the CO 2 RR process is urgent but challenging.…”