Efficient Charge Migration in Chemically-Bonded Prussian Blue Analogue/CdS with Beaded Structure for Photocatalytic H2 Evolution

Electrocatalytic activity of tungsten carbide hybrids with two different MOFs for water splitting: a comparative analysis

Conventional energy resources are diminishing, and environmental pollution is constantly increasing because of the excessive use of fossil fuels to sustain the ever-increasing population and industrialization. This has raised concerns regarding a sustainable future. In the pursuit of addressing sustainability in industrial processes and energy systems, the production of green hydrogen is considered a promising and crucial solution to meet the growing energy demands. Water-splitting is one of the most effective technologies for producing clean and carbon-neutral hydrogen. Water-splitting is a scientifically emerging application, but it is commercially limited due to its economic non-viability. The sluggish kinetics and the high overpotential needed for the water-splitting reactions (HER and OER) have encouraged the scientific community to design electrocatalysts that address the concerns of low activity, efficiency and stability. Designing a hybrid catalyst using metal-organic frameworks (MOFs) with transition metal carbides can be a suitable approach to address the deficiencies of conventional water-splitting catalysts. In this study, we have designed and fabricated an electrocatalyst of tungsten carbide (WC) with two different MOFs (Zr-based and Fe-based) and explored their electrocatalytic activity for hydrogen generation in an alkaline medium. It should be noted that hybrids of tungsten carbide with a zirconia MOF (UiO-66) showed better electrocatalytic activity with low overpotentials of 104 mV (HER) and 152 mV (OER) at a current density of 10 mA cm-2. This superior activity of WC with the Zr-MOF in comparison to the Fe-MOF is due to the synergistic effect of Zr present in UiO-66 grown on the WC matrix. Moreover, UiO-66 provides a larger electrocatalytic active surface area, so available active sites are more in UiO-66 as compared to the Fe-MOF. These findings set the stage for the systematic development and production of bi-functional hybrid catalysts with the potential to be utilized in water-splitting processes.

Molten salt synthesis of 1T/2H mixed phase MoS2 for boosting photocatalytic H2 evolution via Schottky junction under EY-sensitized system

Clean H2 fuel obtained from the photocatalytic water splitting to hydrogen reaction could efficiently alleviate current energy crisis and the concomitant environmental pollution problems. Therefore, it is desirable to search for a highly efficient photocatalytic system to decrease the energy barrier of water splitting reaction. Herein, the 1T/2H mixed phase MoS2 sample with Schottky junction between contact interfaces is developed through molten salt synthesis for photocatalytic hydrogen production under a dye-sensitized system (Eosin Y-TEOA-MoS2) driven by the visible light. In mixed phase MoS2 sample, the photogenerated electrons of 2H-phase MoS2 migrated to the 1T-phase MoS2 are difficult to jump back because of the existence of Schottky barrier, which greatly suppresses the quenching of EY and therefore results in an enhanced hydrogen evolution performance. Therefore, the optimized MoS2 sample (MoS2-350) has an initial hydrogen evolution rate of 213 μmol h-1 and corresponding apparent quantum yield of 36.1 % at 420 nm, far higher than those of pure Eosin Y. It is strongly confirmed by the steady-state/time-resolved photoluminescence (PL) spectra and transient photocurrent response experiments. With the assistance of Density functional theory (DFT) calculation, the function of Schottky junction in photocatalytic hydrogen evolution reaction is well explained. In addition, a new and universal method (SVM curve) of judging oxidation or reduction quenching for photosensitizers is proposed.

Enhanced and synergistic catalytic activation by photoexcitation driven S-scheme heterojunction hydrogel interface electric field

The regulation of heterogeneous material properties to enhance the peroxymonosulfate (PMS) activation to degrade emerging organic pollutants remains a challenge. To solve this problem, we synthesize S-scheme heterojunction PBA/MoS2@chitosan hydrogel to achieve photoexcitation synergistic PMS activation. The constructed heterojunction photoexcited carriers undergo redox conversion with PMS through S-scheme transfer pathway driven by the directional interface electric field. Multiple synergistic pathways greatly enhance the reactive oxygen species generation, leading to a significant increase in doxycycline degradation rate. Meanwhile, the 3D polymer chain spatial structure of chitosan hydrogel is conducive to rapid PMS capture and electron transport in advanced oxidation process, reducing the use of transition metal activator and limiting the leaching of metal ions. There is reason to believe that the synergistic activation of PMS by S-scheme heterojunction regulated by photoexcitation will provide a new perspective for future material design and research on enhancing heterologous catalysis oxidation process.

Chemical Etching and Phase Transformation of Nickel-Cobalt Prussian Blue Analogs for Improved Solar-Driven Water-Splitting Applications

Although Prussian blue and its analogs (PB/PBAs) have open framework structures, large surface areas, uniform metal active sites, and tunable compositions, and have been investigated for a long time, owing to their unfavorable visible light responsiveness, they rarely been reported in photocatalysis. This largely limits their applications in solar-to-chemical energy conversion. Here, a continuous-evolution strategy was conducted to convert the poor-performance NiCo PBA (NCP) toward high-efficiency complex photocatalytic nanomaterials. First, chemical etching was performed to transform raw NCP (NCP-0) to hollow-structured NCP (including NCP-30, and NCP-60) with enhanced diffusion, penetration, mass transmission of reaction species, and accessible surface area. Then, the resultant hollow NCP-60 frameworks were further converted into advanced functional nanomaterials including CoO/3NiO, NiCoP nanoparticles, and CoNi₂S₄ nanorods with a considerably improved photocatalytic H₂ evolution performance. The hollow-structured NCP-60 particles exhibit an enhanced H₂ evolution rate (1.28 mol g^-1h^-1) compared with the raw NCP-0 (0.64 mol g^-1h^-1). Furthermore, the H₂ evolution rate of the resulting NiCoP nanoparticles reached 16.6 mol g^-1h^-1, 25 times that of the NCP-0, without any cocatalysts.

2D Network overtakes 3D for photocatalytic hydrogen evolution

3-Dimensional (3D) cyanide coordination polymers, typically known as Prussian blue Analogues (PBAs), have received great attention in catalysis due to their stability, easily tuned metal sites, and porosity. However, their high crystallinities and relatively low number of surface-active sites significantly hamper their intrinsic catalytic activities. Herein, we report the utilization of a 2-dimensional (2D) layered cobalt tetracyanonickelate, [Co-Ni], for the reduction of protons to H₂. Relying on its exposed facets, layered morphology, and abundant surface-active sites, [Co-Ni] can efficiently convert water and sunlight to H₂ in the presence of a ruthenium photosensitizer (Ru PS) with an optimal evolution rate of 30 029 ± 590 μmol g^-1 h^-1, greatly exceeding that of 3D Co-Fe PBA [Co-Fe] and Co-Co PBA [Co-Co]. Furthermore, [Co-Ni] retains its structural integrity throughout a 6 hour photocatalytic cycle, which is confirmed by XPS, PXRD, and Infrared analysis. This recent work reveals the excellent morphologic properties that promote [Co-Ni] as an attractive catalyst for the hydrogen evolution reaction (HER).

On-Demand Atomic Hydrogen Provision by Exposing Electron-Rich Cobalt Sites in an Open-Framework Structure toward Superior Electrocatalytic Nitrate Conversion to Dinitrogen

Electrocatalytic nitrate (NO₃^-) reduction to N₂ via atomic hydrogen (H*) is a promising approach for advanced water treatment. However, the reduction rate and N₂ selectivity are hindered by slow mass transfer and H* provision-utilization mismatch, respectively. Herein, we report an open-framework cathode bearing electron-rich Co sites with extraordinary H* provision performance, which was validated by electron spin resonance (ESR) and cyclic voltammetry (CV) tests. Benefiting from its abundant channels, NO₃^- has a greater opportunity to be efficiently transferred to the vicinity of the Co active sites. Owing to the enhanced mass transfer and on-demand H* provision, the nitrate removal efficiency and N₂ selectivity of the proposed cathode were 100 and 97.89%, respectively, superior to those of noble metal-based electrodes. In addition, in situ differential electrochemical mass spectrometry (DEMS) indicated that ultrafast *NO₂^- to *NO reduction and highly selective *NO to *N₂O or *N transformation played crucial roles during the NO₃^- reduction process. Moreover, the proposed electrochemical system can achieve remarkable N₂ selectivity without the additional Cl^- supply, thus avoiding the formation of chlorinated byproducts, which are usually observed in conventional electrochemical nitrate reduction processes. Environmentally, energy conservation and negligible byproduct release ensure its practicability for use in nitrate remediation.

Efficient Charge Migration in TiO2@PB Nanorod Arrays with Core-shell Structure for Photoelectrochemical Water Splitting

Herein, the TiO2@Prussian-blue (PB)core-shell nanorod arrays for photoelectrochemical (PEC) application were designed and prepared via a facile hydrothermal and electrodeposition process. Due to the combined merits of anti-reflection structure of...

Enhancing Photocatalytic Hydrogen Production via the Construction of Robust Multivariate Ti-MOF/COF Composite

Titanium metal-organic frameworks (Ti-MOFs), as an appealing type of artificial photocatalysts, have shown great potentials in the field of solar energy conversion due to their well-studied photo-redox activity similar to TiO 2 and good optical responsiveness of linkers serving as the antenna to absorb visible-light. Although enormous efforts have been dedicated to developing Ti-MOFs with high photocatalytic activity, their solar energy conversion performances are still poor. Herein, a covalent-integrated strategy has been implemented to construct a series of multivariate Ti-MOF/COF hybrid materials, PdTCPP⸦PCN-415(NH 2 )/TpPa (composites 1, 2, and 3), featuring excellent visible-light utilization, suitable band gap, and high surface area for photocatalytic H 2 production. Notably, the resulting composites demonstrated remarkably enhanced visible-light-driven photocatalytic H 2 evolution performance, especially for the composite 2 with the maximum H 2 evolution rate of 13.98 mmol g -1 h -1 (turn-over frequency (TOF) = 227 h -1 ), which is much higher than the prototypical counterparts, PdTCPP⸦PCN-415(NH 2 ) (0.21 mmol g -1 h -1 ) and TpPa (6.51 mmol g -1 h -1 ). Our work thereby suggests a new approach to develop highly efficient photocatalysts for photocatalytic H 2 evolution reaction and beyond.

Visible-light-responsive Z-scheme system for photocatalytic lignocellulose-to-H2 conversion

A Z-scheme system was successfully constructed for visible-light-driven photocatalytic H₂ production from lignocelluloses, the highest H₂ evolution rate of this Z-scheme system is 5.3 and 1.6 μmol h^-1 in α-cellulose and poplar wood chip aqueous solutions, respectively, under visible light irradiation.

Exposed (002) facets and controllable thickness of CdS nanobelts drive desirable hydrogen-adsorption free energy (ΔGH) for boosting visible-light photocatalytic performance

The strategies of exposed CdS (002) facets and controllable thickness lead to a desirable value for ΔGH, which can improve the CdS photocatalytic activity.