Toward Stable Solar Hydrogen Generation Using Organic Photoelectrochemical Cells

Abstract

Organic photoactive materials are promising candidates for the generation of solar fuels in terms of efficiency and cost. However, their low stability in aqueous media constitutes a serious problem for technological deployment. Here we present organic photocathodes for the generation of hydrogen in aqueous media with outstanding stability. The device design relies on the use of water-resistant selective contacts, which protect a P3HT:PCBM photoactive layer. An insoluble cross-linked PEDOT:PSS hole-selective layer avoids delamination of the film, and an electron-selective TiO x layer in contact with the aqueous solution electrically communicates the organic layer with the hydrogen-evolving catalyst (Pt). We developed a novel method for the synthesis of the TiO x layer compatible with low-temperature conditions. Tuning the thickness of the TiO x /Pt layer leads to a trade-off between the achievable photocurrent (∼1 mAcm −2) and the stability of the photocathode (stable hydrogen generation of 1.5 μmol h −1 cm −2 for >3 h).

Molecular Catalyst Immobilized Photocathodes for Water/Proton and Carbon Dioxide Reduction

“…[43] The solution-processed fabrication methodm akes this kind of solar cell more promising and more recyclable than other types of solar cells. Some inorganic catalysts, such as MoS 3 [45] and Pt, [46] have been used to accept electrons from the OPV photocathode to perform H 2 evolution in water solution.Afew reports detail the use of molecular catalysts workingt ogether with OPVelectrodes for H 2 evolution. [44] On the basis of the OPV concept, it is also possible to build up ap hotocathode by combining the catalysts for H 2 evolutiona nd CO 2 reduction,a ss hown in Scheme 6.…”

Photoelectrochemical Hydrogen Evolution: Single-Layer, Conjugated Polymer Films Bearing Surface-Deposited Pt Nanoparticles

“…These multilayer systems are demonstrated to achieve photocurrents up to 1 mA cm −2 and a H 2 generation rate of 1.5 μmol h −1 cm −2 . 36 Given the advancements in the field an apparent need for catalysts to promote hydrogen evolution at irradiated conjugated films.…”

Electropolymerized polyaniline: A promising hole selective contact in organic photoelectrochemical cells

“…The observed low stability is similar to that obtained with cross-linked PSS:PEDOT hole selective layer when the same ESL/catalyst was used. [20] In that study, the stability was remarkably improved when a thicker electron selective layer was deposited, but increasing electron conductivity problems within the ESL. For this reason, the mechanisms of loss of performance and the development of protective electron selective layer are currently under investigation in our lab.…”

“…Compared to inorganic devices, usually synthesized by means of high vacuum/high temperature conditions, these devices take full advantage of the versatility and potential of organic semiconductor materials to provide a real low-cost alternative for the generation of solar fuels. [19][20][21] These devices consist of an organic semiconductor material with excellent light harvesting efficiency (in general a P3HT:PCBM bulk heterojunction film is employed) sandwiched by proper selective contacts, compatible with the relevant electrochemical potentials in order to carry out the desired reactions at the semiconductor/solution interface.…”

“…The device is taken outside the glovebox. The TiO x solution[20] was filtered through a nylon filter (0.45 μm pore size) and was spin-coated on the active layer in air at 1000 rpm for 60 s and kept in the ambient at room temperature for 2 h. A thermal treatment at 85 °C for 10 min was observed to be beneficial for the device performance. Thin platinum layer was sputtered by using a BALTEC (SCD 500) sputter coater by using a current of 50 mA for 2−5 s while keeping the distance between Pt source and substrates at ∼5 cm at a base pressure of 5 × 10 −3 mbar.…”