Enhancement of electrocatalytic abilities toward CO reduction by tethering redox-active metal complexes to the active site.

Tethering metal complexes, like [Ru(bpy)Cl] (bpy = 2,2'-bipyridine), which are redox-active at low reduction potentials and have the ability to transfer electrons to another complex, to a [Ni(cyclen)] electrocatalyst enhanced the reduction of CO to CO at low overpotentials. The [Ni(cyclen)] electrocatalyst was modified by tethering redox-active metal complexes 4-methylpyridyl linkers. The redox-active metal complexes were reduced after CO bound to the active site. In controlled potential electrolysis (CPE) experiments in 95 : 5 (v/v) CHCN/HO, [{([Ru]pic)cyclen}NiCl] ([Ru] = {Ru(bpy)Cl}; pic = 4-methylpyridyl) could be used to reduce CO into CO at a turnover frequency (TOF) of 708 s with a faradaic efficiency (FE) of 80% at an onset potential of -1.60 V . NHE. At the same time, this electrocatalyst was active at an onset potential of -1.25 V . NHE, which is the reduction potential of one of the bpy ligands of the [Ru] moieties, with FE = 84% and TOF = 178 s. When the electrocatalysis was performed using [bncyclenNiCl]Cl (bn = benzyl) without tethered redox-active metal complexes, the TOF value was determined to be 8 s with FE = 77% at an onset potential of -1.45 V . NHE. The results show that tethering redox-active metal complexes significantly improves the electrocatalytic activities by lowering the potential needed to reduce CO.