Unraveling a Single-Step Simultaneous Two-Electron Transfer Process from Semiconductor to Molecular Catalyst in a CoPy/CdS Hybrid System for Photocatalytic H₂ Evolution under Strong Alkaline Conditions

Abstract

Electron transfer processes from semiconductor to molecular catalysts was studied in a model hybrid photocatalytic hydrogen evolution system composed of [Co((III))(dmgH)2PyCl] (CoPy) and CdS under different pH conditions. Thermodynamic and kinetic studies revealed that photocatalytic H2 evolution under high pH conditions (pH 13.5) can only account for the thermodynamically more favorable single-step simultaneous two-electron transfer from photoirradiated CdS to Co(III)Py to produce unavoidable intermediate Co(I)Py, rather than a two-step successive one-electron transfer process. This finding not only provides new insight into the charge transfer processes between semiconductors and molecular catalysts but also opens up a new avenue for the assembly and optimization of semiconductor-molecular catalyst hybrid systems processed through multielectron transfer processes.

Solar‐to‐Hydrogen Energy Conversion Based on Water Splitting

“…[44][45][46][47][48][49][50] Domen and co-workers demonstrated the role of the sacrificial reagents in the enhancement of the solar conversion efficiency using the solid solution of GaN and ZnO for visible-light-driven H 2 and O 2 evolution in the presence of methanol and silver nitrate, respectively. [70,71] These QDs have the advantages of broad and efficient absorbance of the visible light, the superior photostability under irradiation and the good dispersion in aqueous solutions. [51] Efficient semiconductors for photocatalytic water splitting include not only the many metal-containing inorganic solids, but also the well-known graphitic carbon nitride (g-C 3 N 4 ).…”

“…They found that both the thermodynamics and kinetics of the redox reactions have an impact on the photocatalytic efficiency. [70] The surface defects are the trapping and recombination sites of the photoexcited carriers, but they are also helpful for the electron transfer from QDs to molecular catalysts. [52][53][54][55][56][57][58][59] The g-C 3 N 4 material has been studied intensively for photocatalytic hydrogen evolution as well as overall water splitting.…”

Recent Advances in First‐Row Transition Metal Clusters for Photocatalytic Water Splitting

“…Cadmium sulfide (CdS) has been studied extensively for use as a H 2 evolution photocatalyst because of the excellent visible‐light response and relatively adequate position of conduction band . However, the applications of single CdS was greatly restricted due to the rapid recombination of photoinduced electron‐hole pairs, severe photocorrosion, and scarce catalytic sites.…”

“…Cadmium sulfide (CdS) has been studied extensively for use as a H 2 evolution photocatalyst because of the excellent visiblelight response and relatively adequate position of conduction band. [6,[120][121][122][123][124] However, the applications of single CdS was greatly restricted due to the rapid recombination of photoinduced electron-hole pairs, severe photocorrosion, and scarce catalytic sites. Various methods, such as coupling CdS with cocatalysts, [123] incorporating doping elements, joining porous 14 (OH) 2 (W 3 O 10 ) 2 (α-SbW 9 O 33 ) 6 ] 27À .…”

Reversibility‐Dependent Photovoltammetric Behavior of Electroactive Compounds on a CdS–Graphene Hybrid Film Electrode

“…In essence, there are two critical factors, namely mass transfer rate and electron transfer rate, which affect the shape of the CV curve . As an n‐type semiconductor, CdS has a flat band potential of −0.69 V (vs. NHE) at pH 6.0, which is much more negative than the half‐wave potential ( E 1/2 ) estimated from the average value of the anodic and cathodic peak potentials for either HQ or K 3 [Fe(CN) 6 ] system, suggesting that the electron transfer from photoirradiated CdS to the oxidized species of HQ and K 3 [Fe(CN) 6 ] is thermodynamically allowed. Meanwhile, the reduction rates of oxidized species of HQ and K 3 [Fe(CN) 6 ] are fast because their reactions are quasi‐reversible and reversible.…”