Exceptional Catalytic Nature of Quantum Dots for Photocatalytic Hydrogen Evolution without External Cocatalysts

The catalytic nature of semiconducting quantum dots (QDs) for photocatalytic hydrogen (H₂) evolution can be thoroughly aroused, not because of coupling with external cocatalysts, but through partially covering controlled amount of ZnS shell on the surface. Specifically, CdSe QDs, with an optimal coverage of ZnS (≈46%), can produce H₂ gas with a constant rate of ≈306.3 ± 21.1 µmol mg^?1 h^?1 during 40 h, thereby giving a turnover number of ≈(4.4 ± 0.3) × 10⁵, which is ≈110‐fold to that of unmodified CdSe QDs under identical conditions. The performance of H₂ evolution is comparable to or even better than the commonly used external cocatalysts, e.g., metal complexes, noble metals assisted photosystems. Mechanistic insights indicate that the dramatically enhanced activity and stability of bare QDs for photocatalytic H₂ production are derived from (i) inhibiting exciton annihilation at trap states, (ii) preventing the photo‐oxidation of core frameworks, and (iii) retaining tunneling efficiencies of photogenerated electrons and holes to reactive sites with partial ZnS coverage.     

Modulating the Photocatalytic Activity of Graphene Quantum Dots via Atomic Tailoring for Highly Enhanced Photocatalysis under Visible Light

Precise control over doping of photocatalysts is required to modulate their photocatalytic activity in visible light‐driven reactions. Here, a single precursor‐employing bottom‐up approach is developed to produce different heteroatom‐doped graphene quantum dots (GQDs) with unique photocatalytic activities. The solvothermal reaction of a norepinephrine precursor with redox active and condensable moieties effectively produces both nitrogen/sulfur codoped GQDs (NS‐GQDs) and nitrogen‐doped GQDs (N‐GQDs) by simply varying solvents (from dimethyl sulfoxide to water) under microwave irradiation. As‐prepared NS‐GQDs and N‐GQDs show similar lateral sizes (3–4 nm) and heights (1–2 nm), but they include different dopant types and doping constitution and content, which lead to changes in photocatalytic activity in aerobic oxidative coupling reactions of various amines. NS‐GQDs exhibit much higher photocatalytic activity in reactions under visible light than N‐GQDs and oxygen‐doped GQDs (O‐GQDs). The mechanism responsible for the outstanding photocatalytic activity of NS‐GQDs in visible light‐driven oxidative coupling reactions of amines is also fully investigated.     

g‐C3N4 Loading Black Phosphorus Quantum Dot for Efficient and Stable Photocatalytic H2 Generation under Visible Light

Black phosphorus (BP) is an interesting two‐dimensional material with low‐cost and abundant metal‐free properties and is used as one cocatalyst for photocatalytic H₂ production. However, the BP quantum dot (BPQD) is not studied. Herein, for the first time, BPQD is introduced as a hole‐migration cocatalyst of layered g‐C₃N₄ for visible‐light‐driven photocatalytic hydrogen generation. A high‐vacuum stirring method is developed for BPQD loading without the dissociation of BP. The layered BPQD is coupled on the layered g‐C₃N₄ surface to form a heterojunction structure. The 7% BPQD–C₃N₄ samples show similar time‐resolved photoluminescence curves as 0.5% Pt–C₃N₄. The optimum hydrogen rates of the modified sample (7% BPQD–C₃N₄) are 190, 133, 90, and 10.4 µmol h^?1 under simulated sunlight, LED‐405, LED‐420, and LED‐550 nm irradiation, respectively, which are 3.5, 3.6, and 3 times larger than that of the pristine g‐C₃N₄. Such low‐cost layered system not only optimizes the optical, electrical, and texture properties of the hybrid materials for photocatalytic water splitting to generate hydrogen but also provides ideas for designing novel or easily oxidized candidates by incorporating different available materials with given carriers.     

In Situ Electrochemical Activation of Atomic Layer Deposition Coated MoS2 Basal Planes for Efficient Hydrogen Evolution Reaction

Molybdenum disulfide (MoS₂), which is composed of active edge sites and a catalytically inert basal plane, is a promising catalyst to replace the state‐of‐the‐art Pt for electrochemically catalyzing hydrogen evolution reaction (HER). Because the basal plane consists of the majority of the MoS₂ bulk materials, activation of basal plane sites is an important challenge to further enhance HER performance. Here, an in situ electrochemical activation process of the MoS₂ basal planes by using the atomic layer deposition (ALD) technique to improve the HER performance of commercial bulk MoS₂ is first demonstrated. The ALD technique is used to form islands of titanium dioxide (TiO₂) on the surface of the MoS₂ basal plane. The coated TiO₂ on the MoS₂ surface (ALD(TiO₂)‐MoS₂) is then leached out using an in situ electrochemical activation method, producing highly localized surface distortions on the MoS₂ basal plane. The MoS₂ catalysts with activated basal plane surfaces (ALD(Act.)‐MoS₂) have dramatically enhanced HER kinetics, resulting from more favorable hydrogen‐binding.     

One‐Pot,Facile, and Versatile Synthesis of Monolayer MoS2/WS2 Quantum Dots as Bioimaging Probes and Efficient Electrocatalysts for Hydrogen Evolution Reaction

In this work, uniform molybdenum disulfide (MoS₂)/tungsten disulfide (WS₂) quantum dots are synthesized by the combination of sonication and solvothermal treatment of bulk MoS₂/WS₂ at a mild temperature. The resulting products possess monolayer thickness with an average size about 3 nm. The highly exfoliated and defect‐rich structure renders these quantum dots plentiful active sites for the catalysis of hydrogen evolution reaction (HER). The MoS₂ quantum dots exhibit a small HER overpotential of ≈120 mV and long‐term durability. Moreover, the strong fluorescence, good cell permeability, and low cytotoxicity make them promising and biocompatible probes for in vitro imaging. In addition, this work may provide an alternative facile approach to synthesize the quantum dots of transition metal dichalcogenides or other layered materials on a large scale.     

Simple and Scalable Mechanochemical Synthesis of Noble Metal Catalysts with Single Atoms toward Highly Efficient Hydrogen Evolution

Designing a facile strategy to access active and atomically dispersed metallic catalysts are highly challenging for single atom catalysts (SACs). Herein, a simple and fast approach is demonstrated to construct Pt catalysts with single atoms in large quantity via ball milling Pt precursor and N‐doped carbon support (K₂PtCl₄@NC‐M; M denotes ball‐milling). The as‐prepared K₂PtCl₄@NC‐M only requires a low overpotential of 11 mV and exhibits 17‐fold enhanced mass activity for the electrochemical hydrogen evolution compared to commercial 20 wt% Pt/C. The superior hydrogen evolution reaction (HER) catalytic activity of K₂PtCl₄@NC‐M can be attributed to the generation of Pt single atoms, which improves the utilization efficiency of Pt atoms and the introduction of Pt‐N₂C₂ active sites with near‐zero hydrogen adsorption energy. This viable ball milling method is found to be universally applicable to the fabrication of other single metal atoms, for example, rhodium and ruthenium (such as Mt‐N₂C₂, where Mt denotes single metal atom). This strategy also provides a promising and practical avenue toward large‐scale energy storage and conversion application.     

Boosting Potassium Storage Kinetics,Stability, and Volumetric Performance of Honeycomb-Like Porous Red Phosphorus via In Situ Embedding Self-Growing Conductive Nano-Metal Networks

Large volume expansion and sluggish reaction kinetics of low-conductivity red phosphorus (RP) anodes hinder its practical application in potassium-ion batteries (PIBs). Here, a self-limited growth strategy to fabricate Bi (Sb) nanoparticles is demonstrated, as electrochemically active and conductive coating, in situ embedded into honeycomb-like porous red phosphorus (HPRP) to form HPRP@Bi (HPRP@Sb) composites, greatly improving the potassium-storage kinetics, stability and volumetric performance of HPRP. Here, Bi nanoparticles are converted into amorphous Bi during cycling, which are uniformly coated on the porous HPRP skeleton to form 3D conductive Bi networks. Theoretical calculations verify that introducing amorphous Bi significantly decreases K⁺ diffusion barrier in composites, and greatly enhancing their electrical conductivity and interfacial ion transport between HPRP and Bi, thereby accelerating their potassium storage kinetics and stability. Whereas the robust porous structure and inward expansion mechanism of HPRP effectively buffer their volume expansion of RP and Bi. Therefore, HPRP@Bi anode delivers high gravimetric and volumetric capacity (465.6 mAh g⁻¹, 745 mAh cm⁻³) and stable long lifespan with 200 cycles at 0.05 A g⁻¹ in PIBs. This work demonstrates a new approach to promote ion storage kinetics and stability of RP via integrating the synergy of high-conductivity active metal and high-capacity porous RP.     

Ultrahigh Mass Activity for the Hydrogen Evolution Reaction by Anchoring Platinum Single Atoms on Active {100} Facets of TiC via Cation Defect Engineering

Improving the platinum (Pt) mass activity for low-cost electrochemical hydrogen evolution is an important and arduous task. Here, a selective etching-reducing fluidized bed reactor technique is reported to create Ti vacancies and firmly anchor single Pt atoms on the active {100} facets of titanium carbide (TiC) to increase the Pt utilization efficiency and improve catalytic activity significantly by a synergistic effect between Ti vacancies and Pt atoms. The generated Ti vacancies are negatively charged and stabilize Pt atoms by forming covalent Pt C bonds, showing excellent long-term durability. Pt single atoms (ultralow load of 1.2 µg cm⁻²) on the defective TiC {100} show remarkable activity (24.9 mV at 10 mA cm⁻²) and a mass activity (49.69 A mg⁻¹) ≈190 times that of the state-of-the-art Pt C catalyst and nearly double the previously reported best values. The developed cation defect engineering exhibits excellent potential for fabricating next-generation advanced single-atom catalysts for large-scale hydrogen evolution at a low cost.