Light to Hydrogen: Photocatalytic Hydrogen Generation from Water with Molecularly-Defined Iron Complexes

Abstract

Photocatalytic hydrogen generation is considered to be attractive due to its combination of solar energy conversion and storage. Currently-used systems are either based on homogeneous or on heterogeneous materials, which possess a light harvesting and a catalytic subunit. The subject of this review is a brief summary of homogeneous proton reduction systems using sacrificial agents with special emphasis on non-noble metal systems applying convenient iron(0) sources. Iridium photosensitizers, which were proven to have high quantum yields of up to 48% (415 nm), have been employed, as well as copper photosensitizers. In both cases, the addition or presence of a phosphine led to the transformation of the iron precursor with subsequently increased activities. Reaction pathways were investigated by photoluminescence, electron paramagnetic resonance (EPR), Raman, FTIR and mass spectroscopy, as well as time-dependent DFT-calculations. In the future, this knowledge will set the basis to design photo(electro)chemical devices with tailored electron transfer cascades and without the need for sacrificial agents.

Comprehensive review and future perspectives on the photocatalytic hydrogen production

“…More recently, interesting reviews have addressed separately each of the three system categories but there is no integrated and comparative analysis of the three systems. The present review provides such an integrated overview of the photocatalytic generation of H 2 , and the influence of the photocatalytic units and process variables on H 2 production rate and stability.…”

Structure–Activity and Stability Relationships for Cobalt Polypyridyl‐Based Hydrogen‐Evolving Catalysts in Water

“…For instance, quantities are strongly influenced even by subtle variations of the different components (e.g., SED, PS, pH, concentrations/ratios, and light source) . There is a great deal of reported information on the initial steps of photocatalysis in homogeneous solutions, that is, the study of the processes that follow excitation of the photosensitizer (reductive/oxidative quenching, first electron transfer to cobalt, and follow‐up reactions of oxidized electron donors), both in organic and aqueous media, as well as in mixtures . There are, from a spectroscopic point of view, only few studies focusing on the follow‐up reactions of the reduced cobalt species in water or organic solvents .…”

[FeFe]‐hydrogenase H‐cluster mimics mediated by mixed (S, Se) and (S, Te) bridging moieties: Insight into molecular structures and electrochemical characteristics

“…In recent years, the production of hydrogen catalyzed by first row transition metals like iron represents promising substitutes of the commonly used platinum, iridium, or rhenium catalysts . Green algae, such as Chlamydomonas reinhardtii , can produce hydrogen using [FeFe]‐hydrogenase system in a very efficient way with turnover frequencies over 10 000 H 2 /s .…”