Lattice-Matched CoP/CoS2 Heterostructure Cocatalyst to Boost Photocatalytic H2 Generation

CdS-based Schottky junctions for efficient visible light photocatalytic hydrogen evolution

Heterojunctions photocatalysts play a crucial role in achieving high solar-hydrogen conversion efficiency. In this work, we mainly focus on the charge transfer dynamics and pathways for sulfides-based Schottky junctions in the photocatalytic water splitting process to clarify the mechanism of heterostructures photocatalysis. Sulfides-based Schottky junctions (CdS/CoP and CdS/1T-MoS2) were successfully constructed for photocatalytic water splitting. Because of the higher work function of CdS than that of CoP and 1T-MoS2, the direction of the built-in electric field is from CoP or 1T-MoS2 to semiconductor. Therefore, CoP and 1T-MoS2 can act as electrons acceptors to accelerate the transfer of photo-generated electron on the surface of CdS, thus improving the charge utilization efficiency. Meanwhile, CoP and 1T-MoS2 as active sites can also promote the water dissociation and lower the H+ reduction overpotential, thus contributing to the excellent photocatalytic hydrogen production activity (23.59 mmol·h-1·g-1 and 1195.8 mol·h-1·g-1 for CdS/CoP and CdS/1T-MoS2).

Interfacial tuning in FeP/ZnIn2S4 Ohm heterojunction: Enhanced photocatalytic hydrogen production via Zn-P charge bridging

Interfacial regulation is key to photocatalytic performance, yet modulating interfacial charge transfer in heterostructures remains challenging. Herein, a novel nanoflower-like FeP/ZnIn2S4 Ohm heterostructure is first designed, with Zn atoms in ZnIn2S4 (ZIS) acting as potential anchoring sites around P atoms, forming liganded Zn-P bonds. Combining 1D FeP nanowires and 2D ZIS nanosheets enhances the mobility of photogenerated electrons. The synergistic chain-type "electron pickup" mechanism of the Ohm heterojunction coupled with the Zn-P bond speeds up electron transport at the interface. The Ohm heterojunction initiates an internal electric field, creating a driving force to further transfer photogenerated electrons through the Zn-P rapid electron transport channel to FeP, which acts as a reservoir for active sites to release H2. The optimized FeP/ZIS demonstrates a remarkable H2 evolution rate at 4.36 mmol h-1 g-1, 3.6 times that of pristine ZIS. This work provides novel insights into optimizing photocarrier dynamics via interfacial microenvironment modulation.

Adjacent Mn site boosts photocatalytic hydrogen evolution of MnXCd1-XS solid solution through a dual-metal-site design

CdS has emerged as a possible candidate for photocatalytic hydrogen generation. However, further improvement in the performance of the Cd metal site is challenging due to limited optimization space. To solve this limitation, in this work, the Mn-Cd dual-metal photocatalyst was synthesized by a one-step solvothermal method, and the effects of different proportions of bimetals on hydrogen production activity were systematically studied. The ingenious design of the bimetallic sites enhances the carrier separation efficiency and the built-in electric field intensity, which leads to significant improvement in the photocatalytic hydrogen production performance of MCS0.19. Density functional theory (DFT) calculations confirm that the introduction of the Mn element can drive electrons through the Fermi level, resulting in enhanced conductivity of the catalyst. Meanwhile, electron channels are built between Mn and S, which speeds up the rate of electron transfer and is conducive to improving hydrogen production activity. This work provides a technical-methodological entrance to improve the photocatalytic hydrogen production performance of dual-metal S solid solutions and also promises to open a novel approach to creating high-efficiency solid solution photocatalysts.

Combined Analyses on Electronic Structure and Molecular Orbitals of d10 Bimetal Oxide In2Ge2O7 and Photocatalytic Performances for Overall Water Splitting and CO2 Reduction

Semiconducting photocatalytic overall water splitting and CO2 reduction are possible solutions to the emerging worldwide challenges of oil shortage and continual temperature increase, and the key is to develop an efficient photocatalyst. Most photocatalysts contain the d0, d10 or d10ns2 metals, and a guiding principle is desired to help to distinguish outstanding semiconductors. Here, the d10 bimetal oxide In2Ge2O7 was selected as the target. First, density functional theory (DFT) calculations point out that the nonbonding O 2p orbitals dominate the valence band maximum (VBM), and In 5s-O 2s and Ge 4s-O 2s antibonding orbitals are the major components of conduction band minimum (CBM). Moreover, the molecular orbitals were analyzed to consolidate the DFT calculations and make it more understandable for chemists. Due to the very small specific surface area (0.51 m2/g) and wide band gap (4.14 eV), as-prepared In2Ge2O7 did not exhibit any overall water splitting activity; nevertheless, when loading with 1 wt% cocatalyst (i.e., Pt, Pd), the surficial charge recombination can be greatly eliminated and the overall water splitting activity is significantly improved to 33.0(4) and 17.2(7) μmol/h for H2 and O2 generation, respectively. The apparent quantum yield (AQY) at 254 nm is 8.28%. This observation is proof that the inherent electronic structure of In2Ge2O7 is beneficial for the charge migration in bulk. Moreover, this catalyst also exhibits an observable CO2 reduction activity in pure water, which is a competition reaction with water splitting, anyway, the CH4 selectivity can be enhanced by loading Pd. This is a successful attempt to unravel the structure-property relationship by combining the analyses on electronic structure and molecular orbitals and is enlightening to further discover good candidates to photocatalysts.

Interface prompted highly efficient hydrogen evolution of MoS2/CoS2 heterostructures in a wide pH range

Interfacial electronic characteristics are crucial for the hydrogen evolution reaction (HER), especially in nanoscale heterogeneous catalysts. In this work, we found that the synergistic activation of CoS₂ and MoS₂ (2H-MoS₂ and 1T-MoS₂) greatly enhances the HER activity in a wide pH range compared to those of each component. The Gibbs free energies for hydrogen adsorption at interfacial Co sites are as low as -0.08 (-0.25) eV and -0.20 (0.01) eV for 2H-MoS₂/CoS₂ and 1T-MoS₂/CoS₂ heterostructures in acidic (alkaline) media, respectively, which are even superior to that of Pt(111) (-0.09 eV). Moreover, the theoretical exchange current density of MoS₂/CoS₂ can reach ∼1.98 × 10^-18 A site^-1 (∼8.43 A mg^-1). Experimentally, MoS₂/CoS₂ exhibits a greatly reduced overpotential of 54 (46) mV and a Tafel slope of 42 (50) mV dec^-1 under acidic (alkaline) conditions. The improved performance mainly originates from the synergistically activated interfacial Co atoms with better electron localization and local bonding. The interfacial effect enhances the electron conductivity and improves the H adsorption characteristics, making MoS₂/CoS₂ highly valuable as efficient HER electrocatalysts.

Deciphering the photocatalytic hydrogen generation process of Fresnoite Ba2TiGe2O8 by electronic structure and bond analyses

In addition to enhancing the activity of already-known photocatalysts, developing new ones is always desired in photocatalysis, giving more opportunities to approach practical applications. Most photocatalysts are composed of d⁰ (i.e. Sc³⁺, Ti⁴⁺, Zr⁴⁺) and/or d¹⁰ (i.e. Zn²⁺, Ga³⁺, In³⁺) metal cations, and a new target catalyst is Ba₂TiGe₂O₈ containing both. Experimentally, it exhibits a UV-driven catalytic H₂ generation rate of 0.5(1) μmol h^-1 in methanol aqueous solution, which could be enhanced to 5.4(1) μmol h^-1 by loading 1 wt% Pt as the cocatalyst. Most interestingly, theoretical calculations together with analyses on the covalent network could help us to decipher the photocatalytic process. The electrons in O 2p non-bonding orbitals are photo-excited to either Ti-O or Ge-O anti-bonding orbitals. The latter interconnect with each other to form an infinite two-dimensional network for electron migration to the catalyst surface, while the Ti-O anti-boding orbitals are rather localized because of the Ti⁴⁺ 3d orbitals; thus, those photo-excited electrons mostly recombine with holes. This study on Ba₂TiGe₂O₈ containing both d⁰ and d¹⁰ metal cations gives an interesting comparison, suggesting that a d¹⁰ metal cation is probably more useful to construct a favorable conduction band minimum for the migration of photo-excited electrons.

Bridging electrocatalyst and cocatalyst studies for solar hydrogen production via water splitting

Solar-driven water-splitting has been considered as a promising technology for large-scale generation of sustainable energy for succeeding generations. Recent intensive efforts have led to the discovery of advanced multi-element-compound water-splitting electrocatalysts with very small overpotentials in anticipation of their application to solar cell-assisted water electrolysis. Although photocatalytic and photoelectrochemical water-splitting systems are more attractive approaches for scaling up without much technical complexity and high investment costs, improving their efficiencies remains a huge challenge. Hybridizing photocatalysts or photoelectrodes with cocatalysts has been an effective scheme to enhance their overall solar energy conversion efficiencies. However, direct integration of highly-active electrocatalysts as cocatalysts introduces critical factors that require careful consideration. These additional requirements limit the design principle for cocatalysts compared with electrocatalysts, decelerating development of cocatalyst materials. This perspective first summarizes the recent advances in electrocatalyst materials and the effective strategies to assemble cocatalyst/photoactive semiconductor composites, and further discusses the core principles and tools that hold the key in designing advanced cocatalysts and generating a deeper understanding on how to further push the limits of water-splitting efficiency.

Dual plasmonic Au and TiN cocatalysts to boost photocatalytic hydrogen evolution

Employing a suitable cocatalyst is very important to improve photocatalytic H2 evolution activity. Herein, two plasmonic cocatalysts, Au nanoparticles and TiN nanoparticles were in-situ coupled over the g-C3N4 nanotube to form a ternary 0D/0D/1D Au/TiN/g-C3N4 composite via a successive thermal polycondensation and chemical reduction method. The g-C3N4 nanotube acted as a support for the growth of Au and TiN nanoparticles, leading to intimate contact between g-C3N4 nanotube with Au nanoparticles and TiN nanoparticles. As a result, multiple interfaces and dual-junctions of Au/g-C3N4 Schottky-junction and TiN/g-C3N4 ohmic-junction were constructed, which helped to promote the charged carriers' separation and enhanced the photocatalytic performance. Furthermore, loading plasmonic cocatalysts of Au nanoparticles and TiN nanoparticles can enhance the light absorption capacity. Consequently, the Au/TiN/g-C3N4 composite exhibited significantly enhanced photocatalytic H2 evolution activity (596 μmol g-1 h-1) compared to g-C3N4 or binary composites of Au/g-C3N4 and TiN/g-C3N4. This work highlights the significant role of cocatalysts in photocatalysis.