Impact of the Dissolved Anion on the Electrocatalytic Reduction of CO₂ to CO with Ruthenium CNC Pincer Complexes

Abstract

The reactivity of three ruthenium electrocatalysts is shown to be modulated through the addition of anions for more selective and faster electrocatalysis. Controlled potential electrolysis studies confirm the generation of CO from CO 2. The Faradaic efficiency increased for the three ruthenium catalysts studied through the introduction of Clto the reaction solution. Interestingly, a neutral ruthenium coordination complex with an associated chloride also gave equal or faster rates of catalysis upon Cl À addition. In this report, a systematic study on the effects of added halides (I À , Br À , Cl À , and F À) with varied counter cations (K + and TBA +) with and without water is examined. Computational analysis provides insights into this interesting increase in FE based on anion addition. These results show anion addition to electrocatalysis reaction mixtures add an additional parameter to increase both rate and selectivity of catalysis with one example improving from 19 % FE to 91 % FE for CO production.

Probing the Effects of Electron Deficient Aryl Substituents and a π‐System Extended NHC Ring on the Photocatalytic CO2 Reduction Reaction with Re‐pyNHC‐Aryl Complexes**

“…Interestingly, these complexes show increased current at the first reduction wave under CO 2 . This is a property that has been observed by several NHC complexes during the electrocatalytic CO 2 RR in the literature [8] and is hypothesized to be due to the second reduction occurring after association to CO 2 and being less thermodynamically demanding than the first reduction prior to CO 2 association to the catalyst [9] …”

“…This is a property that has been observed by several NHC complexes during the electrocatalytic CO 2 RR in the literature [8] and is hypothesized to be due to the second reduction occurring after association to CO 2 and being less thermodynamically demanding than the first reduction prior to CO 2 association to the catalyst. [9] The energetic position of the excited-state reduction potentials (E (S*/SÀ ) ) of the catalysts are important to evaluate when considering possible sacrificial electron donor (SED) materials to drive the PCO 2 RR. The E (S*/SÀ ) values were estimated to be 0.88 V to 1.07 V from the equation E (S*/SÀ ) = E (MLCT-GS) + E (S/ SÀ ) .…”

“…13 C NMR (100 MHz, CD 3 CN): δ 144. 9,143.3,140.3,133.7,129.3 (q,J = 32.5 Hz),127.72 (q,J = 3.8 Hz),124.8,124.5,123.3,122.1 (q, J = 269.0 Hz), 111.3 ppm. One signal may not be unique.…”

N-Heterocyclic Carbene Gold Complexes in a Photocatalytic CO2 Reduction Reaction

“…Chloride-ligated complexes being faster CO 2 reduction catalysts than the presumably MeCN-ligated complexes has been previously attributed to a more easily dissociated anionic ligand upon reduction of the complex. 42 After 72 h, all catalysts retain some activity with TOF F values ranging from 0.1 to 0.5 h −1 . A chloride-labile ligand is compared to a phenyl group via complexes 4 Cl and 4 Ph .…”

“…A proposed catalytic cycle is shown in Figure with the roles of Ir(ppy) 3 , BIH, TEA, and the Au catalyst depicted. Addition of a Au catalyst to CO 2 upon opening a reactive site is proposed based on prior cyclic voltammetry studies on 1 Cl and common observations in the literature that NHC-ligated metals favor the addition of CO 2 after a single electron reduction of the metal complex leading to the opening of a reactive site. − The series of catalysts being probed in this study also allow analysis of how varied labile ligands promote entry into the catalytic cycle. Additionally, NHC ligand variations allow for probing of how the addition of Au complexes to CO 2 and the subsequent protonation, C–O bond cleavage, and CO dissociation steps are affected in the catalytic cycle.…”