A Stable Alkylated Cobalt Catalyst for Photocatalytic H₂ Generation in Liposomes

Abstract

Photocatalytic proton reduction is a promising way to produce dihydrogen (H 2 ) in a clean and sustainable manner, and mimicking nature by immobilising proton reduction catalysts and photosensitisers on liposomes is an attractive approach for biomimetic solar fuel production in aqueous solvents. Current photocatalytic proton reduction systems on liposomes are, however, limited by the stability of the catalyst. To overcome this problem, a new alkylated cobalt(II) polypyridyl complex (CoC 12 ) was synthesised and immobilised on the lipid bilayer of liposomes, and its performance was studied in a photocatalytic system containing an alkylated ruthenium photosensitiser (RuC 12 ) and a 1 : 1 mixture of sodium ascorbate and tris-2carboxyethylphosphine hydrochloride as sacrificial electron donors. Several parameters (concentration of CoC 12 and RuC 12 , pH, membrane composition) were changed to optimise the turnover number for H 2 production. Overall, CoC 12 was found to be photostable and the optimised turnover number (161) was limited only by the decomposition of the ruthenium-based photosensitiser.

Bioinspired photocatalytic systems towards compartmentalized artificial photosynthesis

“… a Liposome embedding a synthetic molecular CPQ triad, quinone and a F 0 -F 1 -ATP synthase for electron and proton transfer across the membrane with concomitant pH gradient generation coupled to the synthesis of ATP reported by A. Moore et al, 96 ( b ) proteoliposome embedding MtrCAB from S. oneidensis MR-1 and encapsulated N 2 O reductase for electron transfer across membrane with N 2 O-to-N 2 reduction reported by J. N. Butt et al, 58 ( c ) polymersome embedding donor and acceptor molecules at each domain of the membrane for transmembrane energy transfer reported by Y. Zheng, Y. Zhou et al, 119 ( d ) polymersome with embedded bacteriorhodopsin a F 0 -F 1 -ATP synthase for transmembrane proton transfer coupled to ATP synthesis reported by T. Vidaković-Koch et al, 99 ( e ) liposome containing a Ru-PS and a Ru-WOC for light-driven WO reported by L. Sun, B. König et al, 127 ( f ) liposome with a Ru-PS and a Co-HEC for light-driven HER reported by B. König et al, 132 ( g ) liposome with a Ru-PS and a Co-HEC for light-driven HER reported by S. Bonnet et al, 130 ( h ) liposome with a Ru-PS and a CoPc-CO 2 RC for light-driven CO 2 reduction to CO reported by L. Hammarström, E. Reisner et al, 93 ( i ) liposome with a HER-MOF embedded in the hydrophobic membrane and an encapsulated WO-MOF for overall light-driven WS reported by W. Lin, C. Wang et al 140 . …”

“…The potential of artificial vesicles to develop compartmentalized systems for reductive transformations has also garnered substantial attention. In this context, liposome- and other membrane-based systems for photocatalytic HER 130 – 133 , CO 2 R 93 , 134 – 136 , and organic transformations 58 , 103 , have been reported.…”

“…In another example, S. Bonnet et al developed 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (NaDSPE-PEG2K) based liposomes containing the modified hydrophobic [Ru(bpy) 3 ] 2+ PS together with an alkylated Co(II) polypyridyl HEC for photocatalytic HER. Mechanistic studies showed that the activity was limited to the decomposition of the Ru-PS 130 .…”

Gatekeeping Effect of Ancillary Ligand on Electron Transfer in Click Chemistry‐Linked Tris‐Heteroleptic Ruthenium(II) Donor–Photosensitizer–Acceptor Triads

“…This helps in understanding and improving, e.g., dye‐sensitized photocatalysis on surfaces, i.e., dye‐sensitized photoelectrochemical cells [ 1–4 ] or dye‐sensitized solar cells (DSSCs), [ 5–7 ] in light‐driven catalysis, [ 8,9 ] energy storage, [ 10–13 ] and biomimetic photocatalytic systems. [ 14–18 ]…”

“…This helps in understanding and improving, e.g., dyesensitized photocatalysis on surfaces, i.e., dye-sensitized photoelectrochemical cells [1][2][3][4] or dye-sensitized solar cells (DSSCs), [5][6][7] in light-driven catalysis, [8,9] energy storage, [10][11][12][13] and biomimetic photocatalytic systems. [14][15][16][17][18] Within the context of light-driven hydrogen formation, pioneering work by Kiwi and Grätzel [19] and subsequently, Sakai and Ozawa [20] did show that the combination of light absorption, charge transfer, and storage of redox equivalents on viologen-type molecules rendered highly active photocatalytic systems. Covalent linkage between viologen electron acceptors and catalytically active metal centers led to an overall improvement of catalytic activity with respect to attainable turnover numbers and frequencies.…”