To
realize the evolution of C2+ hydrocarbons like C2H4 from CO2 reduction in photocatalytic
systems remains a great challenge, owing to the gap between the relatively
lower efficiency of multielectron transfer in photocatalysis and the
sluggish kinetics of C–C coupling. Herein, with Cu-doped zeolitic
imidazolate framework-8 (ZIF-8) as a precursor, a hybrid photocatalyst
(CuOX@p-ZnO) with CuOX uniformly dispersed among
polycrystalline ZnO was synthesized. Upon illumination, the catalyst
exhibited the ability to reduce CO2 to C2H4 with a 32.9% selectivity, and the evolution rate was 2.7
μmol·g–1·h–1 with
water as a hole scavenger and as high as 22.3 μmol·g–1·h–1 in the presence of triethylamine
as a sacrificial agent, all of which have rarely been achieved in
photocatalytic systems. The X-ray absorption fine structure spectra
coupled with in situ FT-IR studies reveal that, in the original catalyst,
Cu mainly existed in the form of CuO, while a unique Cu+ surface layer upon the CuO matrix was formed during the photocatalytic
reaction, and this surface Cu+ site is the active site
to anchor the in situ generated CO and further perform C–C
coupling to form C2H4. The C–C coupling
intermediate *OC–COH was experimentally identified by in situ
FT-IR studies for the first time during photocatalytic CO2 reduction. Moreover, theoretical calculations further showed the
critical role of such Cu+ sites in strengthening the binding
of *CO and stabilizing the C–C coupling intermediate. This
work uncovers a new paradigm to achieve the reduction of CO2 to C2+ hydrocarbons in a photocatalytic system.