Self-Assembled Liposomes Enhance Electron Transfer for Efficient Photocatalytic CO₂ Reduction

Light-driven conversion
of CO2 to chemicals provides
a sustainable alternative to fossil fuels, but homogeneous systems
are typically limited by cross reactivity between different redox
half reactions and inefficient charge separation. Herein, we present
the bioinspired development of amphiphilic photosensitizer and catalyst
pairs that self-assemble in lipid membranes to overcome some of these
limitations and enable photocatalytic CO2 reduction in
liposomes using precious metal-free catalysts. Using sodium ascorbate
as a sacrificial electron source, a membrane-anchored alkylated cobalt
porphyrin demonstrates higher catalytic CO production (1456 vs 312
turnovers) and selectivity (77 vs 11%) compared to its water-soluble
nonalkylated counterpart. Time-resolved and steady-state spectroscopy
revealed that self-assembly facilitates this performance enhancement
by enabling a charge-separation state lifetime increase of up to two
orders of magnitude in the dye while allowing for a ninefold faster
electron transfer to the catalyst. Spectroelectrochemistry and density
functional theory calculations of the alkylated Co porphyrin catalyst
support a four-electron-charging mechanism that activates the catalyst
prior to catalysis, together with key catalytic intermediates. Our
molecular liposome system therefore benefits from membrane immobilization
and provides a versatile and efficient platform for photocatalysis.