Light-driven electrocatalytic reduction of CO₂ on silicon nanowires using Mn bipyridyl complex catalysts

E.Torralba-Penalver^a, Sylvie Chardon^b and Bruno Fabre^a

^a Matière Condensée et Systèmes Electroactifs (MaCSE), UMR 6226 Institut des Sciences Chimiques de Rennes, Université de Rennes 1, 35042 Rennes Cedex, France

^b Université de Grenoble, Département de Chimie Moléculaire, UMR5250, Grenoble, France

Proton-assisted multielectron reduction potentials for CO₂ lie within the bandgap of several semiconductors, in such a way that their use as photocathodes for this reaction allows a substantial decrease in the energy input required [1-3]. In the present work, hydrogen-terminated silicon nanowires (SiNWs-H) are used as a photocathode for the electrocatalytic reduction of CO₂ in the presence of different metallic bipyridyl complexes. Due to its nanostructured surface, SiNWs are highly interesting as light-harvesting electrodes, being efficient in converting solar to electrical energy, easy to make and stable under reduction conditions [4]. Among the tested complexes, we have used Mn non-noble metal based complexes to catalyze CO₂-to-CO photoelectroreduction, which is a less expensive approach versus the traditionally used based on rare and noble metal complexes [5]. The photoelectrochemical reduction of CO₂ at p-type SiNWs-H was achieved at potentials significantly lower than those required with a glassy carbon electrode (GCE) [6]. Thus, for intermediate reduction potentials the photocurrent density values provided by silicon were noticeably higher than the current densities provided by GCE. Besides, impedance spectroscopic measurements were carried out and combined with cyclic voltammetry data to obtain the quantitative complete characterization of the energetics of all the systems studied. All the experiences were carried out at p-type flat silicon for comparison purposes and key electrocatalytic parameters such as fill factor (FF) and energy conversion efficiency (η) were determined. Finally, in order to develop technologically viable electrocatalytic devices, the elaboration of SiNWs−H photoelectrodes modified with a Mn-based complex has been successfully achieved from an electropolymerizable catalyst, and it was shown that the electrocatalytic activity of the complex was retained after immobilization. 

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