phore-catalyst assembly for solar CO 2 reduction †

We describe here the preparation and characterization of a photocathode assembly for CO2 reduction to CO in 0.1 M LiClO4 acetonitrile. The assembly was formed on 1.0 mm 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-RuCP2 -Re(I), where DA is the dianiline-based electron donor (N,N,N0,N0-((CH2)3PO3H2)4-4,40-dianiline), RuCP 2+ is the light absorber [Ru((4,40-(PO3H2CH2)2-2,20bipyridine)(2,20-bipyridine))2] , and Re(I) is the CO2 reduction catalyst, Re ((4,40-PO3H2CH2)2-2,20bipyridine)(CO)3Cl. Visible light excitation of the assembly in CO2 saturated solution resulted in CO2 reduction to CO. A steady-state photocurrent density of 65 mA 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 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 t1/2 1⁄4 2.6 ms (kET 1⁄4 2.7 10 s ).