Photoelectrochemical CO<sub>2</sub> Reduction to CO Enabled by a Molecular Catalyst Attached to High-Surface-Area Porous Silicon
Xiaofan Jia, Eleanor Stewart-Jones, Jose L. Alvarez-Hernandez, Gabriella P. Bein, Jillian L. Dempsey, Carrie L. Donley, Nilay Hazari, Madison N. Houck, Min Li, James M. Mayer, Hannah S. Nedzbala, Rebecca E. Powers
Abstract
A high-surface-area p -type porous Si photocathode containing a covalently immobilized molecular Re catalyst is highly selective for the photoelectrochemical conversion of CO 2 to CO. It gives Faradaic efficiencies of up to 90% for CO at potentials of −1.7 V (versus ferrocenium/ferrocene) under 1 sun illumination in an acetonitrile solution containing phenol. The photovoltage is approximately 300 mV based on comparisons with similar n -type porous Si cathodes in the dark. Using an estimate of the equilibrium potential for CO 2 reduction to CO under optimized reaction conditions, photoelectrolysis was performed at a small overpotential, and the onset of electrocatalysis in cyclic voltammograms occurred at a modest underpotential. The porous Si photoelectrode is more stable and selective for CO production than the photoelectrode generated by attaching the same Re catalyst to a planar Si wafer. Further, facile characterization of the porous Si-based photoelectrodes using transmission mode FTIR spectroscopy leads to highly reproducible catalytic performance.