Utilization of CO2 as a carbon source for production of CO and syngas using a ruthenium(II) electrocatalyst

Abstract

A new mononuclear Ru(II) complex, [Ru(phen-dione)(CH3CN)4](PF6)2 (phen-dione = 1,10-phenanthroline-5,6-dione), (I), has been synthesized and structurally characterized revealing a distorted octahedral environment around the central ruthenium(II) cation. The electrocatalytic activity of the complex was investigated for the reduction CO2 to CO in an acetonitrile solution using cyclic voltammetry under different reaction conditions (concentration of electrocatalyst, temperature, and scan rate). An increase in the complex concentration, or the scan rate led to a higher CO2 reduction peak current. Moreover, the electrocatalytic activity of (I) decreased at lower temperatures, because the activation energy is inversely temperature-dependent. Further, (I) was used for the electrocatalytic reduction of CO2 to CO and simultaneous reduction of H2PO4– as a hydrogen source to produce syngas with a tunable mole ratio of H2:CO by changing and controlling the H2PO4– concentration whereby the mole ratio of H2:CO increases with increasing amount of added H2PO4–. Consequently, the produced syngas had a wide range with respect to the H2:CO mole ratio (0–2.4). The proposed mechanisms for the electrocatalytic reduction of CO2 to CO and H2 evolution from H2PO4– in the presence of (I) were confirmed using density functional theory (DFT) calculations.