Pyridine‐functionalized N‐heterocyclic carbene gold(I) binuclear complexes as molecular electrocatalysts for oxygen evolution reactions

Abstract

N‐heterocyclic carbene (NHC) complexes of gold(I/III) attained immense interest in catalytic organic transformations and as anticancer agents against several types of human cancers; however, their potential as electrocatalysts is scarce. The electrocatalytic oxygen evolution reaction was performed for the first time using pyridine‐functionalized NHC gold(I) binuclear metallacycles (8 and 9) possessing aptly designed ligand field. Complexes were prepared by the transmetallation of corresponding silver(I) NHC complexes, which were prepared by in situ deprotonation of pyridine and aryl substituted 1,2,4‐triazolium hexafluorophosphate salts (6 and 7) with Ag2O under dark. Both triazolium salts and binuclear gold(I) metallacycles were thoroughly characterised by NMR and ATR‐IR spectral and elemental analyses. A bromide salt 4 and a binuclear gold complex 9 were elucidated for structure by single crystal X‐ray diffraction analysis. Complex 9 possesses distorted linear coordination geometry around the gold atoms by the coordination of carbene carbon and pyridine nitrogen atoms bearing close Au–Au interaction (3.251 Å). The binuclear gold complexes 8 and 9 (along with 10 wt% conductive mesoporous carbon) were investigated as molecular electrocatalysts in oxygen evolution reaction (OER), which evidenced an oxygen evolution overpotential of 2.422 and 2.370 V versus reversible hydrogen electrode (RHE), respectively, to attain a current density of 10 mA.cm−2. The Tafel slope values of 40.9 and 30.4 mV dec−1 for 8 and 9, respectively, indicate the reaction mechanism involved and the suitability of these complexes as apt electrocatalysts for OER. The stability of the prepared molecular electrocatalysts was investigated by cyclic voltammetry and chronoamperometry techniques.

Augmenting the Electrocatalytic Activities of Metal–N-Heterocyclic Carbene Complexes as Bifunctional Electrocatalysts for Hydrogen and Oxygen Evolution Reactions by Carbon Composite Strategy

“…This forecasting is on the basis of stability and their typical activity as molecular electrocatalysts, and their combination with carbon composites would lead to the achievement of promising electrocatalytic HER and OER activities. Recently, a series of metal–NHC complexes have been reported for the electrocatalytic activity, , and here is the resumption of our work derived from the functionalized NHC ligand. We narrate the synthesis and a combination of structural characterization techniques and electrocatalytic activity of a series of metal–NHCs as bifunctional electrocatalysts along with carbon supports to accomplish the promising activity.…”

Comprehensive enhancement in electrocatalytic oxygen evolution performance of nickel and cobalt complexes derived from π-conjugated N-heterocyclic carbene ligands through carbon composite strategy

“…Recently, a series of metal–NHC complexes have been reported to exhibit good catalytic performance in the OER. 15 These metal–NHC complexes have found to be stable in alkaline electrolyte and the diversity of the metal atoms and the varying ligand systems adds to the activity of the resulting complexes as electrocatalysts. 15 The synthesis of metal–NHC complexes from the azolium salts leads to an enormous reinforcement in the interest of the ease in preparation methods to obtain diverse structural motifs of metal NHC-complexes.…”

“…15 These metal–NHC complexes have found to be stable in alkaline electrolyte and the diversity of the metal atoms and the varying ligand systems adds to the activity of the resulting complexes as electrocatalysts. 15 The synthesis of metal–NHC complexes from the azolium salts leads to an enormous reinforcement in the interest of the ease in preparation methods to obtain diverse structural motifs of metal NHC-complexes. 16 The focus on transition-metal compounds of heterocyclic carbenes has its roots in the peculiar properties of carbenes when attached to a metal.…”

Palladium(II)–N-Heterocyclic Carbene Complex-Based Electrocatalysts for Hydrogen Evolution Reaction

“…The viable variations that can be observed in its stereo-electronic characteristics by alternating and tuning the NHC backbone and the wingtip substitutions are also added advantages . Notably, the advantage of employing NHC complexes is their low metal content with maximum efficiency in catalysis, and also, the modification of the electrode in electrocatalysis is more homogeneous since the NHC complexes form an ink in highly polar solvents . Palladium–NHC metal complexes as heterogeneous electrocatalysts are rather unusual and unconventional; however, given their advantages as mentioned, it is not unexpected that these class of catalysts have eventually been found under the lens of electrochemistry.…”