Recent findings and future directions in photosynthetic hydrogen evolution using polypyridine cobalt complexes

Abstract

The production of hydrogen gas using water as the molecular substrate currently represents one of the most challenging and appealing reaction schemes in the context of Artificial Photosynthesis (AP), i.e.,...

Rethinking Electronic Effects in Photochemical Hydrogen Evolution Using CuInS2@ZnS Quantum Dots Sensitizers

“…A fixed concentration of both QDs (0.11 mM) and ascorbate (0.5 M) was used in all photochemical tests. The experimental data obtained in terms of moles of hydrogen produced as a function of the irradiation time (kinetic traces) were properly employed in order to extract the relevant photocatalytic parameters [ 5 ]: (i) the maximum turnover number (TON) calculated as the ratio between the maximum quantity of hydrogen produced (in moles) and the quantity of catalyst employed (in moles), (ii) the maximum turnover frequency (TOF/h −1 ) calculated as the ratio between the initial rate of hydrogen production (in mol/h, estimated in the linear portion of the kinetic trace) and the moles of catalyst, and (iii) the quantum efficiency (QE/%) calculated as the ratio between two-times the initial rate of hydrogen formation (in mol/h) and the absorbed photon flux (in Einstein/h).…”

“…Hydrogen production via light-driven water splitting is recognized as a candidate fundamental reaction for the generation of clean fuels [ 1 , 2 ]. For this purpose, one of the simplest approaches envisions the coupling in an aqueous solution of three molecular components, namely a light-harvesting sensitizer, a hydrogen evolving catalyst (HEC), and an electron donor [ 3 , 4 , 5 ]. Ideally, this latter component should be constituted by the water molecule itself, leading to the production of oxygen.…”

“…Within the aforementioned three-component system, the reaction scheme usually requires a sequence of events involving (i) the excitation of the sensitizer, (ii) reductive quenching of the excited state by the sacrificial electron donor, (iii) activation of the HEC via two step-wise electron transfer processes from the reduced sensitizer [ 5 ]. Common light-harvesting units employed for the light-driven HER are molecular sensitizers such as coordination compounds, e.g., [Ru(bpy) 3 ] 2+ (where bpy = 2,2′-bipyridine), [ 7 , 8 , 9 , 10 , 11 ], copper(I) or iridium(III) complexes [ 12 , 13 ], or metalloporphyrins [ 4 , 14 ].…”

“…The stability of a photochemical system for hydrogen evolution requires specific care on the catalytic routine as well. Within this framework, cobalt polypyridine complexes have demonstrated improved stability over molecular analogues under operation in aqueous conditions [ 5 ]. We have recently reported on a series of cobalt polypyridine complexes C0–4 featuring hexadentate ligands with diverse electronic substituents on either the bipyridine or the pyridine groups ( Figure 1 a) [ 27 ].…”

A Stable Alkylated Cobalt Catalyst for Photocatalytic H2 Generation in Liposomes

“…Control experiments performed in absence of one of each component (Table 1, Figure S3) confirmed that no H 2 evolved when any one of them were absent from the catalytic mixture. Notably, no photocatalytic activity was observed in absence of TCEP, although many hydrogen evolution systems based on ruthenium‐based photosensitisers and cobalt‐based catalysts are reported to operate with solely HAsc – as sacrificial electron donor [30] …”