Molecular Engineering of Conjugated Acetylenic Polymers for Efficient Cocatalyst-free Photoelectrochemical Water Reduction.

Conjugated polymers featuring tunable band gaps/positions and tailored active centers, are attractive photoelectrode materials for water splitting. However, their exploration falls far behind their inorganic counterparts. Herein, we demonstrate a molecular engineering strategy for the tailoring aromatic units of conjugated acetylenic polymers from benzene- to thiophene-based. The polarized thiophene-based monomers of conjugated acetylenic polymers can largely extend the light absorption and promote charge separation/transport. The C≡C bonds are activated for catalyzing water reduction. Using on-surface Glaser polycondensation, as-fabricated poly(2,5-diethynylthieno[3,2-b]thiophene) on commercial Cu foam exhibits a record H2 -evolution photocurrent density of 370 µA cm-2 at 0.3 V vs. reversible hydrogen electrode among current cocatalyst-free organic photocathodes (1-100 µA cm-2 ). This approach to modulate the optical, charge transfer, and catalytic properties of conjugated polymers paves a critical way toward high-activity organic photoelectrodes.

Simultaneously Accelerating Carrier Transfer and Enhancing O2/CH4 Activation via Tailoring the Oxygen-Vacancy-Rich Surface Layer for Cocatalyst-Free Selective Photocatalytic CH4 Conversion.

Solar energy-driven direct CH4 conversion to liquid oxygenates provides a promising avenue toward green and sustainable CH4 industry, yet still confronts issues of low selectivity toward single oxygenate and use of noble-metal cocatalysts. Herein, for the first time, we report a defect-engineering strategy that rationally regulates the defective layer over TiO2 for selective aerobic photocatalytic CH4 conversion to HCHO without using noble-metal cocatalysts. (Photo)electrochemical and in situ EPR/Raman spectroscopic measurements reveal that an optimized oxygen-vacancy-rich surface disorder layer with a thickness of 1.37 nm can simultaneously promote the separation and migration of photogenerated charge carriers and enhance the activation of O2 and CH4, respectively, to •OH and •CH3 radicals, thereby synergistically boosting HCHO production in aerobic photocatalytic CH4 conversion. As a result, a HCHO production rate up to 3.16 mmol g-1 h-1 with 81.2% selectivity is achieved, outperforming those of the reported state-of-the-art photocatalytic systems. This work sheds light on the mechanism of O2-participated photocatalytic CH4 conversion on defective metal oxides and expands the application of defect engineering in designing low-cost and efficient photocatalysts.

Switching charge transfer process of carbon nitride and bismuth vanadate by anchoring silver nanoparticle toward cocatalyst free water reduction.

With the aim of exploring and modulating the interfacial charge kinetics, a ternary g-C3N4/Ag/BiVO4 was constructed with excellent photocatalytic performance and preferable stability toward H2 evolution in absence of cocatalyst. Both density functional theory (DFT) and experimental results implied that the type II g-C3N4/BiVO4 composite can be switched to Z-scheme via Ag nanoparticles as the electron shuttle. The optimal photocatalytic H2 yield rate achieved for g-C3N4/Ag/BiVO4 was 57.4 µmol·g-1·h-1, being far surpassed the H2 harvest rate of g-C3N4/BiVO4, Ag/g-C3N4 and g-C3N4, which is 2.9, 14.8 and 1.7 µmol·g-1·h-1, respectively. The apparent quantum efficiency of g-C3N4/Ag/BiVO4 photocatalyst was also determined to be 1.23%. Besides, the photocatalytic performance of g-C3N4/Ag/BiVO4 well preserved over 5 runs in 50 h. The improved H2 production performance is considered as the consequence of promoted segregation of photoexcited charge carriers and SPR effects of Ag nanoparticles. In combination with photocurrent measurement, examination of active species and DFT calculation, it is found that Ag nanoparticles as an electron mediator can highly promote the Z-scheme carrier migration that electrons come from conduction band of BiVO4 will quickly assemble with the photo-induced holes from valence band of g-C3N4, leaving electrons in the conduction band of g-C3N4 and holes in valence band of BiVO4 that could greatly enhance the charge separation efficiency.