Photoelectrochemical Reduction of CO_2 at Poly(4- Vinylpyridine)-Stabilized Copper(Ⅰ) Oxide Semiconductor: Feasibility of Interfacial Decoration with Palladium Cocatalyst

摘要

Poly(4-vinylpyridine)-modified copper(Ⅰ) oxide photocathodes, bare or decorated with palladium nanoparticles, can be used for the visible-light-driven selective reduction of CO_2, mostly to methanol and carbon monoxide (in the absence of Pd cocatalyst) or formic acid and carbon monoxide (in the presence of Pd cocatalyst). The photocathode materials, which are composed of hierarchically deposited (onto transparent fluorine-doped conducting glass electrode) Cu_2O (inner layer) and poly(4-vinylpyridine) (P4VP) polyelectrolyte film (outer-layer), with or without dispersed Pd nanoparticles, have been fabricated and examined using electrochemical methodology, atomic force microscopy, and various spectroscopic techniques, including the Raman approach. While the physicochemical characteristics of Cu_2O, including the oxide identity and its semiconducting properties, are not largely affected by the interfacial modification with P4VP, the photostability of the hybrid photocathode is significantly improved. The P4VP-modified Cu_2O exhibits reasonable durability during photoelectrochemical reduction of CO_2 upon illumination with sunlight in semi-neutral medium (Na_2SO_4). While Cu_2O can be identified using Raman spectroscopy as the sole bulk component of the semiconducting film, the XPS data imply that the Cu_2O surface is likely to be partially reduced during prolonged operation. Introduction of palladium cocatalyst seems to improve distribution (collection and transport) of photoelectrons at the photoelectrochemical interface and affects the CO_2-electroreduction mechanism.