Molecular Engineering of Photocathodes based on Polythiophene Organic Semiconductors for Photoelectrochemical Hydrogen Generation

Abstract

Organic semiconductors provide significant potentials for the construction of photoelectrochemical (PEC) cells for solar hydrogen production because of their highly tunable properties. Herein, on carbon fiber paper (CFP) surface, pyridyl (Py), and 4,4′-bipyridin-1-ium (Py2 +) groups were introduced into polythiophene (pTH) semiconductor by electrochemical copolymerization, respectively. After assembly with the Co­(dmgBF2)2 type catalyst (CoB, dmgBF2 = difluoroboryldimethylglyoximate), the CoB@Py2 +-pTH/CFP photocathode displayed nearly twice the photocurrent enhancement (550 μA cm–2 at 0.15 V vs reversible hydrogen electrode, RHE) comparing to that generated by the CoB@Py-pTH/CFP photocathode (290 μA cm–2 at 0.15 V vs RHE) for light-driven H2 generation under AM 1.5 solar illumination. Investigation of the mechanism revealed that the introduction of the positively charged pyridinium groups could improve the intrinsic Co­(dmgBF2)2 catalyst activity for the H2 generation reaction. Meanwhile, the positively charged pyridinium groups serve as p-type dopants to increase the semiconductor bulk charge transfer rate and act as electron transfer mediators to promote the interfacial charge transfer kinetics between the catalyst and the pTH-based organic semiconductor.

Molecular-Modified Photocathodes for Applications in Artificial Photosynthesis and Solar-to-Fuel Technologies

“…The construction of molecular-based light-harvesting complexes and electron donor–acceptors has provided fundamental insights regarding energy and charge transfer processes. This includes the fabrication of purely molecular assemblies ,− as well as molecular components interfaced with solid-state, inorganic materials to form dye-sensitized solar cells and dye-sensitized photo­electrosynthetic cells. − However, this review specifically focuses on photo­electrosynthetic cells featuring solid-state, visible-light-absorbing semiconductors (Figure ) modified with molecular fuel-forming electrocatalysts.…”

HfCoS/rGO Bifunctional Electrocatalysts for Efficient Water Splitting in Alkaline Media

“…Several research groups are attempting to develop effective combinations of transition-metal-based catalysts to address this problem, including metal sulfides, phosphides, selenides, and chalcogenides. − Many groups have attempted inorganic- and organic-based catalysts for the HER and OER with partial accomplishment in producing commercially viable H 2 and O 2 . Nevertheless, low-cost and highly stable active electrocatalysts for H 2 and O 2 production have been reported. − Among the transition metals, Co-based compounds have bifunctional activities. Co-based electrocatalysts are well known for overall water splitting owing to their high stability, low cost, and excellent performance toward HERs and OERs. , Hafnium-based catalysts are potential electrocatalytic materials, particularly for sluggish OERs, and they can be excellent hydrogen storage materials.…”

Bulk Heterojunction Organic Semiconductor Photoanodes: Tuning Energy Levels to Optimize Electron Injection

“…11 This makes the choice of OSCs in PEC devices important to ensure proper thermodynamic driving force for photogenerated charge transfer and necessitates proper interfacial engineering to ensure sufficient charge transfer rates and to avoid charge accumulation. While these aspects are beginning to become apparent in recent literature on the H 2 -producing OSC-based photocathodes, 14,15 the optimization of OSC materials and interfaces for O 2 -producing BHJ photoanodes remains underdeveloped and is particularly challenging given the harsh PEC environment of water oxidation. From a thermodynamic point of view, for an OSC to successfully oxidize water, its highest occupied molecular orbital (HOMO) needs to be less than −5.67 eV vs vacuum (eV vac ) or 1.23 V vs the normal hydrogen electrode (V NHE ) at pH 0, which is the standard water oxidation redox potential (…”

“…This makes the choice of OSCs in PEC devices important to ensure proper thermodynamic driving force for photogenerated charge transfer and necessitates proper interfacial engineering to ensure sufficient charge transfer rates and to avoid charge accumulation. While these aspects are beginning to become apparent in recent literature on the H 2 -producing OSC-based photocathodes, , the optimization of OSC materials and interfaces for O 2 -producing BHJ photoanodes remains underdeveloped and is particularly challenging given the harsh PEC environment of water oxidation.…”