Département de chimie moléculaire

The electrocatalytic redn. of CO2 to CO in hydroorg. medium was studied at illuminated ($łambda$ {\textgreater} 600 nm; 20 mW cm-2) H-terminated Si nanowires (SiNWs-H) photocathodes using three Mn-based carbonyl bipyridyl complexes as homogeneous mol. catalysts ([Mn(L) (CO)3(MeCN)](PF6) and [Mn(bpy) (CO)3Br] with L = bpy = 2,2'-bipyridine and dmbpy = 4,4'-dimethyl-2,2'-bipyridine). Systematic comparison of their cyclic voltammetry characteristics with those obtained at flat H-terminated Si and traditional glassy C electrodes (GCE) enabled the authors to demonstrate the superior catalytic efficiency of SiNWs-H in terms of cathodic photocurrent densities and overpotentials. For example, the photocurrent densities measured at -1.0 V vs. SCE for [Mn(bpy) (CO)3(MeCN)](PF6) at SiNWs-H exceeded 1.0 mA cm-2 in CO2-satd. MeCN + 5{%} vol./vol. H2O, whereas almost zero current was measured at this potential at GCE. Such characteristics were supported by the energetic diagrams built for the different SiNWs|Mn-based catalyst interfaces. The fill factor FF and energy conversion efficiency $η$ calcd. under catalytic conditions were higher for [Mn(bpy or dmbpy) (CO)3(MeCN)](PF6) (FF = 0.35 and 0.34; $η$ = 3.0 and 2.0{%}, resp.). Further preparative-scale electrolysis at SiNWs-H photocathode with Mn-based complex catalysts in electrolytic soln. evidenced the quant. conversion of CO2 to CO with a higher stability of the [Mn(dmbpy) (CO)3(MeCN)](PF6) complex. Finally, to develop technol. viable electrocatalytic devices, the elaboration of SiNWs-H photoelectrodes modified with a Mn-based complex was successfully achieved from an electropolymerizable catalyst, and the electrocatalytic activity of the complex was retained after immobilization. [on SciFinder(R)]