Molecular Organic Sensitizers for Photoelectrochemical Water Splitting

Abstract

The photoelectrochemical approach to photoinduced water splitting is gaining increasing interest for solar fuels generation. Dye‐sensitized photoelectrochemical cells (DS‐PEC) have been studied to improve the collection of the Vis range of solar radiation. Metal complexes have so far been the most investigated dyes but in recent years metal‐free organic dyes have emerged as a new frontier for the evolution of the sector. This Minireview systematically describes the use of organic sensitizers and has been organized in terms of dye‐sensitized photoactive electrode(s): photoanode; photocathode; tandem DS‐PEC with photoanode and photocathode. The main classes of dyes are introduced and described in their key properties, device performance, and water splitting data. Thanks to the increasing number of articles, this review highlights the growing importance of organic sensitizers and their molecular design for a more efficient solar generation of clean fuels.

Synthetic Organic Design for Solar Fuel Systems

“…Overcoming the parasitic, fast electron recombination in PS‐catalyst systems as well as suppressing the need for a SED are current challenges in colloidal and homogeneous schemes. Anchoring a dye and catalyst onto a p‐type SC (p‐SC) electrode to produce a dye‐sensitized photocathode (DSPC, Figure b) is a promising strategy inspired by p‐type DSCs to address these limitations . PS 9 (Figure ) was co‐anchored to a nanostructured NiO substrate together with a cobaloxime HEC .…”

Dye–catalyst dyads for photoelectrochemical water oxidation based on metal-free sensitizers

“…The photoelectrodes typically consist of a wide bandgap semiconductor (SC), which can be sensitized adequately by a dye to extend the absorbed spectrum into the visible region. 8,9 In the case of a DS-PEC with only a photoactive anode, a platinum wire is used as a passive cathode. The sensitizer is adsorbed or chemically bonded onto the SC surface, while the WOC, typically a ruthenium complex, could be either dispersed in aqueous media 10,11 or adsorbed onto the SCs surface.…”

“…[14][15][16] The absence in the literature of organic dyes in dye-WOC dyads for photoanodes is surprising, considering the emerging role of metal-free dyes in the elds of solar energy conversion. 8,[17][18][19] Only two examples of dyads containing organic dyes have been so far reported, but both referred to photoactive cathodes. 20,21 We thus decided to investigate a dyad where a metal-free sensitizer is covalently bonded to a typical WOC, oen used as a catalyst benchmark (a derivative of [Ru(bda)(pic) 2 ] (bda ¼ 2,2 0 -bipyridine-6,6 0 -dicarboxylate; pic ¼ 4-picoline)).…”

“…The CBZ donor building block has been selected as a versatile sulphur-free alternative to the commonly used phenothiazine scaffold. 8,18,26 The central pyrrole-like ring ensures the strong electron-donor character. 27 The presence of the two benzofused benzene rings can be exploited to easily build the two (p-A) arms carrying the terminal cyanoacrylic acceptor-anchoring groups.…”

A diketopyrrolopyrrole dye-based dyad on a porous TiO2 photoanode for solar-driven water oxidation

“…[12][13][14] However, dyad photoanodes typically rely on precious-metal chromophores, and the need for reduced cost has led to the exploration of earth-abundant chromophores with more intense visible light absorption, embodied by metal porphyrins 15 and organic dyes. 16 An example of a zinc porphyrin-based dyad has been reported, but the chromophoric unit lacks sufficient oxidation potential for light-activation of the [Ru(bda)]-based WOC. 15 Organic dyes, frequently designed with push-pull architectures, have been coimmobilised with [Ru II (bda)]-type catalysts on dye-sensitised photoanodes, albeit with low efficiencies.…”