Immobilization of molecular electrocatalysts with retention of catalytic activity is necessary if they will be incorporated into functional photoelectrochemical devices. Most often, immobilization diminishes catalytic performance. Glassy-carbon electrodes covalently modified with [Fe 4 N(CO) 12 ] − are active for electrocatalytic formate production from CO 2 at −1.2 V vs SCE in aqueous solutions buffered at pH 5−9. The modified electrodes are stable for at least 4 days, as demonstrated using cyclic voltammetry experiments. Electrode modification was performed via cycloaddition of alkyne-functionalized [Fe 4 N(CO) 12 ] − with azide-modified glassy-carbon electrodes.
Fe 4 N(CO) 12 ] − is a first-row transition element electrocatalyst that selectively produces C−H bonds to give formate from CO 2 in water at −1.2 V vs SCE. We present a thermochemical analysis which probes the possibility that [H-Fe 4 N(CO) 12 ] 2− ((H-1) 2− ) is an intermediate in this process: we show that (H-1) 2− is accessible at −1.2 V vs SCE, but if it were formed, we predict that it would generate H 2 .[Fe 4 N(CO) 12 ] 3− and (H-1) 2− were interrogated spectroscopically, and the product of CO loss, [Fe 4 N(CO) 9 (μ-CO) 2 ] 3− , was synthesized and characterized. Ultimately, we demonstrate that (H-1) 2− is an unlikely participant in the catalytic transformation of CO 2 to formate.
Metrics & More Article Recommendations * sı Supporting Information ABSTRACT: [Fe 4 N(CO) 12 ] − and [Fe 3 MnO(CO) 12 ] − have the same total electron count and overall charge, as well as similar reduction potentials of −1.21 and −1.17 V vs SCE in MeCN, respectively. Both clusters form the reduced hydride upon single electron transfer (ET) and proton transfer (PT). It is known that [Fe 4 N(CO) 12 ] − is an electrocatalyst for selective CO 2 reduction to formate at −1.2 V vs SCE in either pH 7 buffered water or in MeCN/ H 2 O (95:5) and an effective electrocatalyst for H + reduction to H 2 under N 2 under the same conditions. In contrast, [Fe 3 MnO(CO) 12 ] − affords no products upon electrolysis, beyond [H-Fe 3 MnO(CO) 12 ] − . We determine that [H-Fe 3 MnO(CO) 12 ] − is a weaker hydride donor than [H-Fe 4 N(CO) 12 ] − by about 4 kcal mol −1 , and this is a breaking of the hydricity versus reduction potential scaling relationship previously established for a series of metal carbonyl clusters electrocatalysts.
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