A donor-chromophore-catalyst assembly for solar CO2 reduction

摘要

We describe here the preparation and characterization of a photocathode assembly for CO _(2) reduction to CO in 0.1 M LiClO _(4) acetonitrile. The assembly was formed on 1.0 μm thick mesoporous films of NiO using a layer-by-layer procedure based on Zr( IV )–phosphonate bridging units. The structure of the Zr( IV ) bridged assembly, abbreviated as NiO|-DA-RuCP _(2) ~(2+) -Re( I ), where DA is the dianiline-based electron donor ( N , N , N ′, N ′-((CH _(2) ) _(3) PO _(3) H _(2) ) _(4) -4,4′-dianiline), RuCP ~(2+) is the light absorber [Ru((4,4′-(PO _(3) H _(2) CH _(2) ) _(2) -2,2′-bipyridine)(2,2′-bipyridine)) _(2) ] ~(2+) , and Re( I ) is the CO _(2) reduction catalyst, Re ~(I) ((4,4′-PO _(3) H _(2) CH _(2) ) _(2) -2,2′-bipyridine)(CO) _(3) Cl. Visible light excitation of the assembly in CO _(2) saturated solution resulted in CO _(2) reduction to CO. A steady-state photocurrent density of 65 μA cm ~(?2) was achieved under one sun illumination and an IPCE value of 1.9% was obtained with 450 nm illumination. The importance of the DA aniline donor in the assembly as an initial site for reduction of the RuCP ~(2+) excited state was demonstrated by an 8 times higher photocurrent generated with DA present in the surface film compared to a control without DA. Nanosecond transient absorption measurements showed that the expected reduced one-electron intermediate, RuCP ~(+) , was formed on a sub-nanosecond time scale with back electron transfer to the electrode on the microsecond timescale which competes with forward electron transfer to the Re( I ) catalyst at t _(1/2) = 2.6 μs ( k _(ET) = 2.7 × 10 ~(5) s ~(?1) ).