Active Cocatalysts for Photocatalytic Hydrogen Evolution Derived from Nickel or Cobalt Amine Complexes

Accelerating Nickel-Based Molecular Construction via DFT Guidance for Advanced Photocatalytic Hydrogen Production

Understanding the nickel-based molecular catalyst structure and functional relationship is crucial for catalytic hydrogen production in aqueous solutions. Density functional theory (DFT) provides mature theoretical knowledge for efficient catalyst design, significantly reducing catalyst synthesis time and energy consumption. In the present work, three molecular catalysts, Ni(qbz)(pys)₂ (qbz = 2-quinoline benzimidazole) (NQP 1), Ni(qbo)(pys)₂ (qbo = 2-quinoline benzothiazole) (NQP 2), and Ni(pbz)(pys)₂ (pbz = 4-chloro-2,2-pyridylbenzimidazole) (NQP 3) (pys = 2-mercaptopyridine), were designed and synthesized and exhibit a high performance for H₂ generation in aqueous solution with a lamp (λ ≥ 400 nm) under visible light irradiation. Under the optimal conditions, a H₂ evolution rate as high as 1190 μmol h^-1 can be obtained over 25 mg of NQP 1 with the best catalytic performance. DFT has been adopted in this study to unveil the relationship between the ligand qbz and catalyst NQP 1─an efficient step in the design of catalysts with an excellent catalytic performance. We show that, in addition to the presence of the triphenyl ring increasing the overall electron density, rapid electron transfer (ET) from excited fluorescein (Fl) to NQP 1 significantly improves the chance of photogenerated electrons transferring to the active site, ultimately increasing the catalytic activity for H₂ production. This work on understanding the correlation between structures and properties of complexes provides a new idea for manufacturing high-performance photocatalysts.

Optimizing Atomic Hydrogen Desorption of Sulfur-Rich NiS1+ x Cocatalyst for Boosting Photocatalytic H2 Evolution

Low-cost transition-metal chalcogenides (MS_x ) are demonstrated to be potential candidate cocatalyst for photocatalytic H₂ generation. However, their H₂ -generation performance is limited by insufficient quantities of exposed sulfur (S) sites and their strong bonding with adsorbed hydrogen atoms (SH_ads ). To address these issues, an efficient coupling strategy of active-site-enriched regulation and electronic structure modification of active S sites is developed by rational design of core-shell Au@NiS_{1+ x} nanostructured cocatalyst. In this case, the Au@NiS_{1+ x} cocatalyst can be skillfully fabricated to synthesize the Au@NiS_{1+ x} modified TiO₂ (denoted as TiO₂ /Au@NiS_{1+ x} ) by a two-step route. Photocatalytic experiments exhibit that the resulting TiO₂ /Au@NiS_{1+ x} (1.7:1.3) displays a boosted H₂ -generation rate of 9616 µmol h^-1 g^-1 with an apparent quantum efficiency of 46.0%  at 365 nm, which is 2.9 and 1.7 times the rate over TiO₂ /NiS_{1+ x} and TiO₂ /Au, respectively. In situ/ex situ XPS characterization and density functional theory calculations reveal that the free-electrons of Au can transfer to sulfur-enriched NiS_{1+ x} to induce the generation of electron-enriched S^{δ -} active centers, which boosts the desorption of H_ads for rapid hydrogen formation via weakening the strong SH_ads bonds. Hence, an electron-enriched S^{δ -} -mediated mechanism is proposed. This work delivers a universal strategy for simultaneously increasing the active site number and optimizing the binding strength between the active sites and hydrogen adsorbates.

Red Phosphorus: An Up-and-Coming Photocatalyst on the Horizon for Sustainable Energy Development and Environmental Remediation

Photocatalysis is a perennial solution that promises to resolve deep-rooted challenges related to environmental pollution and energy deficit through harvesting the inexhaustible and renewable solar energy. To date, a cornucopia of photocatalytic materials has been investigated with the research wave presently steered by the development of novel, affordable, and effective metal-free semiconductors with fascinating physicochemical and semiconducting characteristics. Coincidentally, the recently emerged red phosphorus (RP) semiconductor finds itself fitting perfectly into this category ascribed to its earth abundant, low-cost, and metal-free nature. More notably, the renowned red allotrope of the phosphorus family is spectacularly bestowed with strengthened optical absorption features, propitious electronic band configuration, and ease of functionalization and modification as well as high stability. Comprehensively detailing RP's roles and implications in photocatalysis, this review article will first include information on different RP allotropes and their chemical structures, followed by the meticulous scrutiny of their physicochemical and semiconducting properties such as electronic band structure, optical absorption features, and charge carrier dynamics. Besides that, state-of-the-art synthesis strategies for developing various RP allotropes and RP-based photocatalytic systems will also be outlined. In addition, modification or functionalization of RP with other semiconductors for promoting effective photocatalytic applications will be discussed to assess its versatility and feasibility as a high-performing photocatalytic system. Lastly, the challenges facing RP photocatalysts and future research directions will be included to propel the feasible development of RP-based systems with considerably augmented photocatalytic efficiency. This review article aspires to facilitate the rational development of multifunctional RP-based photocatalytic systems by widening the cognizance of rational engineering as well as to fine-tune the electronic, optical, and charge carrier properties of RP.

Photocatalytic Hydrogen Evolution Coupled with Production of Highly Value-Added Organic Chemicals by a Composite Photocatalyst CdIn2 S4 @MIL-53-SO3 Ni1/2

Photocatalytic water splitting coupled with the production of highly value-added organic chemicals is of significant importance, which represents a very promising pathway for transforming green solar energy into chemical energy. Herein, we report a composite photocatalyst CdIn₂ S₄ @MIL-53-SO₃ Ni_1/2 , which is highly efficient on prompting water splitting for the production of H₂ in the reduction half-reaction and selective oxidation of organic molecules for the production of highly value-added organic chemicals in the oxidation half-reaction under visible light irradiation. The superior photocatalytic properties of the composite photocatalyst CdIn₂ S₄ @MIL-53-SO₃ Ni_1/2 should be ascribed to coating suspended ion catalyst (SIC), consisting of redox-active Ni^II ions in the anionic pores of coordination network MIL-53-SO₃ ^- , on the surface of photoactive CdIn₂ S₄ , which endows photogenerated electron-hole pairs separate more efficiently for high rate production of H₂ and selective production of highly value-added organic products, demonstrating great potential for practical applications.

Boosting photocatalytic hydrogen production activity by a microporous II nanoribbon decorated with Pt nanoparticles

Due to the synergistic effect between photoactive Cu^II and Pt sites, the Pt(4.38 wt%)/Cu^II-MOF nanoribbon exhibits an enhanced hydrogen production rate, obviously higher by 4.7 and 1.9 times than those of the individual Pt nanoparticle and Cu^II-MOF.

Copper catalysts for photo- and electro-catalytic hydrogen production

Square planar 1, square pyramidal 2 and trigonal bipyramidal 3 copper complexes are poor catalysts for hydrogen evolution (HER) under photocatalytic conditions, whereas 1 is, or forms, a good and enduring electrocatalyst for HER, but 2 and 3 do not.

MoS2-Stratified CdS-Cu2-xS Core-Shell Nanorods for Highly Efficient Photocatalytic Hydrogen Production

Heterojunction photocatalysts are widely adopted for efficient water splitting, but ion migration can seriously threaten the stability of heterojunctions, as with the well-known low stability of CdS-Cu_2-xS due to intrinsic Cu⁺ ion migration. Here, we utilize Cu⁺ migration to design a stratified CdS-Cu_2-xS/MoS₂ photocatalyst, in which Cu^I@MoS₂ (Cu^I-intercalated within the MoS₂ basal plane) is created by Cu⁺ migration and intercalation to the adjacent MoS₂ surface. The epitaxial vertical growth of the Cu^I@MoS₂ nanosheets on the surface of one-dimensional core-shell CdS-Cu_2-xS nanorods forms catalytic and protective layers to simultaneously enhance catalytic activity and stability. Charge transfer is verified by kinetics measurements with femtosecond time-resolved transient absorption spectroscopy and direct mapping of the surface charge distribution with a scanning ion conductance microscope. This design strategy demonstrates the potential of utilizing hybridized surface layers as effective catalytic and protective interfaces for photocatalytic hydrogen production.

A Z-scheme ZnIn2S4/Nb2O5 nanocomposite: constructed and used as an efficient bifunctional photocatalyst for H2 evolution and oxidation of 5-hydroxymethylfurfural

A bifunctional Z-scheme ZnIn₂S₄/Nb₂O₅ photocatalyst was fabricated, which can be used both for hydrogen evolution and HMF oxidation.

Conjugated nanoporous polycarbazole bearing a cobalt complex for efficient visible-light driven hydrogen evolution

A conjugated nanoporous polycarbazole (CNP) cross-linked by pyridine and coordinated to Co(iii) displays high catalytic performance for visible light-driven H₂ generation.

Boosting Photocatalytic Hydrogen Production by Modulating Recombination Modes and Proton Adsorption Energy

Solar-driven production of renewable energy (e.g., H₂) has been investigated for decades. To date, the applications are limited by low efficiency due to rapid charge recombination (both radiative and nonradiative modes) and slow reaction rates. Tremendous efforts have been focused on reducing the radiative recombination and enhancing the interfacial charge transfer by engineering the geometric and electronic structure of the photocatalysts. However, fine-tuning of nonradiative recombination processes and optimization of target reaction paths still lack effective control. Here we show that minimizing the nonradiative relaxation and the adsorption energy of photogenerated surface-adsorbed hydrogen atoms are essential to achieve a longer lifetime of the charge carriers and a faster reaction rate, respectively. Such control results in a 16-fold enhancement in photocatalytic H₂ evolution and a 15-fold increase in photocurrent of the crystalline g-C₃N₄ compared to that of the amorphous g-C₃N₄.

In situ construction of WO3/g-C3N4 composite photocatalyst with 2D–2D heterostructure for enhanced visible light photocatalytic performance

A WO₃/g-C₃N₄ composite photocatalyst with 2D–2D heterostructure was designed and constructed by an in situ preparation strategy.

Self-template synthesis of double-layered porous nanotubes with spatially separated photoredox surfaces for efficient photocatalytic hydrogen production

Improving charge carriers separation to achieve high photoconversion efficiency in heterogeneous photocatalysts is highly desirable. Herein, heterostructured ZnS@CdS double-layered porous nanotubes (PNTs), in which the spatially separated reduction and oxidation reaction sites lie on the outer and inner shell, respectively, are fabricated through a robust self-template conversion strategy. After selective photo-deposition of Ni and CoO_x as dual cocatalysts, Ni nanoparticles as electron collectors and reduction reaction sites are loaded on the outer shell, while CoO_x nanoparticles as hole collectors and oxidation reaction sites are loaded on the inner shells. As a result, a novel CoO_x/ZnS@CdS/Ni photocatalyst is obtained and shows high visible-light-driven photocatalytic hydrogen production activity owing to the synergistic effect of self-template-derived thin mesoporous heterojunctions and photo-deposition-derived spatially separated dual cocatalysts, which can significantly provide driving force for the ordered transfer of photogenerated electrons and holes toward opposite direction and promote the surface catalytic reaction. Additionally, the facile strategy can be broadened to the preparation of CoO_x/ZnSe@CdSe/Ni PNTs with enhanced photocatalytic activity.

Photocatalytic Deuteration of Halides Using D2 O over CdSe Porous Nanosheets: A Mild and Controllable Route to Deuterated Molecules

A facile and efficient method for deuterium incorporation has been developed by merging photocatalytic C-X bond dissociation and water splitting with porous CdSe nanosheets as the photocatalyst under mild reaction conditions. This reaction displays good functional group tolerance and high selectivity with regard to the number and position of incorporated deuterium atoms, and can be used for the construction of complex molecules in tandem processes.