Phenyl-incorporated carbon nitride photocatalyst with extended visible-light-absorption for enhanced hydrogen production from water splitting.

Developing and employing photocatalysts with extended visible-light-absorption has emerged as a fundamental issue for the enhanced capability of photocatalytic H2 evolution from water splitting. Herein, a wide-spectrum light-responsive phenyl-grafted carbon nitride photocatalyst was synthesized. It was found that benzonquanmine-derived g-C3N4 (BCN) exhibits significantly extended light absorption (∼670 nm) compared with conventional melamine-derived g-C3N4 (MCN). Correspondingly, the photocatalytic H2-evolution rate of BCN (2846 µmol h-1 g-1) is five times as that of MCN under visible-light irradiation. Particularly, an impressive H2-evolution rate of 58 µmol h-1 g-1 could be achieved on BCN even under light irradiation beyond 620 nm. The outstanding photocatalytic H2-evolution performance could be not only attributed to the enriched photons generated from the enhanced solar energy harvesting, but also to the distinctly inhibited rapid recombination of photogenerated electron-hole pairs resulting from the incorporation of phenyl groups. This work furnishes a new train of thought for the designing of carbon-nitride-based photocatalysts with enhanced capability of visible-light-utilization.

Operational Spectroelectrochemical Investigation on the Interfacial Charge Dynamics of Copper Bismuth Oxide Based Photocathode.

Copper bismuth oxide (CBO) is an emerging photocathode in photoelectrochemical (PEC) water splitting but exhibits limited performance due to the severe recombination of photogenerated charges at the semiconductor-liquid junction (SCLJ). For the first time, a set of operational spectroelectrochemical experiments including electrochemical impedance spectroscopy (EIS), transient photocurrent spectroscopy (TPS), and intensity-modulated photocurrent/voltage spectroscopy (IMVS, IMPS) are designed to investigate the charge dynamics at the SCLJ. It is indicated that there are dense surface states above the valence band of CBO, inducing the "Fermi level pinning" (FLP) effect at the SCLJ. The kinetic parameters speculated by IMVS and IMPS indicate the charge transfer efficiency of below 10% with even a bias of ∼0.7 V applied. TPS confirms the sluggish dynamics because of the charging behavior of the surface states. It is expected that this work would provide new connotations of charge dynamics at the SCLJ for the further optimization of CBO-based PEC systems.

Instability Issues and Stabilization Strategies of Lead Halide Perovskites for Photo(electro)catalytic Solar Fuel Production.

Photo(electro)catalysis is a promising route to utilizing solar energy to produce valuable chemical fuels. In recent years, lead halide perovskites (LHPs) as a class of high-performance semiconductor materials have been extensively used in photo(electro)catalytic solar fuel production because of their excellent photophysical properties. However, instability issues make it arduous for LHPs to achieve their full potential in photo(electro)catalysis. This Perspective discusses the instability issues and summarizes the stabilization strategies employed for prolonging the stability or durability of LHPs in photo(electro)catalytic solar fuel production. The strategies for particulate photocatalytic systems (including composition engineering, surface passivation, core-shell structures construction, and solvent selection) and for thin-film PEC systems (including physical protective coating, A site cation additive, and surface/interface passivation) are introduced. Finally, some challenges and opportunities regarding the development of stable and efficient LHPs for photo(electro)catalysis are proposed.

Photocatalytic overall water splitting without noble-metal: Decorating CoP on Al-doped SrTiO3.

CoP, a noble-metal-free cocatalyst, was first introduced onto the surface of Al-doped SrTiO3 (Al:STO) via an in situ photodeposition-phosphorization method for photocatalytic overall water splitting (POWS) into stoichiometric H2 and O2. Compared with pure Al:STO, the POWS activity was enhanced by a factor of ~ 421 over 1.0%CoP/Al:STO, with the highest evolution rates of 2106 and 1002 µmol h-1 g-1 for H2 and O2, respectively. The mechanism for the remarkably boosted POWS activity was systematically analyzed based on the comprehensive characterization. On the one hand, benefiting from the in situ photodeposition process, CoP with metallic character were intimately decorated onto the surface of Al:STO and accelerated the separation and migration of photoinduced charge carriers. On the other hand, CoP, serving as reactive sites for H2 evolution reaction, lowered the overpotential and facilitated the surface reduction reaction, thereby enhancing the POWS activity. Furthermore, Cr2O3 was photodeposited on the surface of 1.0%CoP/Al:STO composite to suppress the undesired reverse reaction and the POWS activity was further enhanced up to 3558 and 1722 µmol h-1 g-1 for H2 and O2, respectively, with apparent quantum yield of 7.1% at 350 ± 10 nm. This work presents a new avenue for designing POWS system without noble-metal cocatalyst.

Integrated Z-Scheme Nanosystem Based on Metal Sulfide Nanorods for Efficient Photocatalytic Pure Water Splitting.

Developing efficient metal sulfides for pure water splitting is a challenging topic in the field of photocatalysis. Herein, inspired by natural photosynthesis, an all-solid-state Z-scheme photocatalyst was constructed with Cd0.9 Zn0.1 S (CZS) for water reduction, red phosphorus (RP) for water oxidation, and metallic CoP as the electron mediator. RP@CoP core-shell nanostructures were uniformly attached on the CZS nanorods, which gave rise to multiple monodispersed nanojunctions. The integrated Z-scheme nanosystem exhibited an apparent quantum efficiency of 6.4 % at 420 nm for pure water splitting. Theoretical analysis and femtosecond transient absorption results revealed that the impressive performance was mainly due to efficient hole transfer of CZS, resulting from the intimate atomic contacts between CoP mediator and photocatalysts, together with favorable band alignment. Meanwhile, the multiple monodispersed Z-scheme nanojunctions could provide abundant reaction sites, which was also important for the boosted activity.

First-Principles Investigation of ß-FeOOH for Hydrogen Evolution: Identifying Reactive Sites and Boosting Surface Reactions.

Akaganeite (ß-FeOOH) is a widely investigated candidate for photo(electro)catalysis, such as water splitting. Nevertheless, insights into understanding the surface reaction between water and ß-FeOOH, in particular, the hydrogen evolution reaction (HER), are still insufficient. Herein, a set of first-principles calculations on pristine ß-FeOOH and halogen-substituted ß-FeOOH are applied to evaluate the HER performance through the computational hydrogen electrode model. The results show that the HER on ß-FeOOH tends to occur at Fe sites on the (010) surface, and palladium and nickel are found to serve as excellent co-catalysts to boost the HER process, due to the remarkably reduced free energy change of hydrogen adsorption upon loading on the surface of ß-FeOOH, demonstrating great potential for efficient water splitting.