Highest Hydrogen Evolution Rate Research Articles

Symmetry‐breaking of Dibenzo[b,d]thiophene Sulfone Enhancing Polaron Generation for Boosted Photocatalytic Hydrogen Evolution

The current bottleneck in the development of efficient photocatalysts for hydrogen evolution is the limited availability of high‐performance acceptor units. Over the past nine years, dibenzo[b,d]thiophene sulfone (DBS) has been the preferred choice for the acceptor unit. Despite extensive exploration of alternative structures as potential replacements for DBS, a superior substitute remains elusive. In this study, a symmetry‐breaking strategy was employed on DBS to develop a novel acceptor unit, BBTT‐1SO. The asymmetric structure of BBTT‐1SO proved beneficial for increasing multiple moment and polarizability. BBTT‐1SO‐containing polymers showed higher efficiencies for hydrogen evolution than their DBS‐containing counterparts by up to 166%. PBBTT‐1SO exhibited an excellent hydrogen evolution rate (HER) of 222.03 mmol g−1 h−1 and an apparent quantum yield of 27.5% at 500 nm. Transient spectroscopic studies indicated that the BBTT‐1SO‐based polymers facilitated electron polaron formation, which explains their superior HERs. PBBTT‐1SO also showed 14% higher HER in natural seawater splitting than that in deionized water splitting. Molecular dynamics simulations highlighted the enhanced water‐PBBTT‐1SO polymer interactions in salt‐containing solutions. This study presents a pioneering example of a substitute acceptor unit for DBS in the construction of high‐performance photocatalysts for hydrogen evolution.

Ti3C2 MXene flakes assisted Mn0.5Cd0.5S/Ti3C2 MXene/g-C3N4 Z-scheme heterojunction for enhancing photocatalytic hydrogen evolution

Efficient carrier separation and high electron migration efficiency are essential for sustainable H2 energy production via photocatalysis. In this work, a Mn0.5Cd0.5S/Ti3C2 MXene/g-C3N4 all-solid-state Z-scheme photocatalyst is constructed by a series of processes, including low temperature calcination, etching, ultrasonication and solvothermal process. The appropriate energy band structures of g-C3N4 and Mn0.5Cd0.5S enable the formation of the Z-scheme system, achieving efficient carrier separation. The Ti3C2 MXene flakes assembled between g-C3N4 nanosheets and Mn0.5Cd0.5S particles can accelerate the charge migration rate in the system. The optimized ternary composite exhibits the highest hydrogen evolution rate (HER) of 13.7 mmol g−1 h−1, which is much higher than that of the pure g-C3N4 and Mn0.5Cd0.5S. Meanwhile, the apparent quantum yield (AQY) value of the composite at 420 nm reaches up to 24.07 % and exhibits high stability. Based on the characterization, the photocatalytic mechanism of carrier transfer in the Z-scheme heterojunction is also revealed. The finding of this article provides insights into the high efficiency of carrier transfer and separation in the photocatalytic reactions.

Optimized synthesis of Fe-doped Ohmic Schottky heterojunctions for efficient NO3− photocatalytic reduction to generate N2

Capacitive Fe-doped Ni2P(Fe2xNi2(1-x)P) is synthesized via the modified solvothermal method to form Ohmic Schottky heterojunctions with monolayer Ti3C2 (MLTC). The composite (10 % 0.1FNP/CdS-2 % MLTC) achieved a high hydrogen evolution rate (HER) of 19.18 mmol·h−1 with a 50 mg sample. In a mere span of 3 h, an impressive NO3− reduction of 0.42 mg/L was achieved, accompanied by an exceptional 92 % N2 selectivity. Quantum efficiency (QE) can reach 56.22 % (λ = 475 nm) by adding 0.1FNP and MLTC. In contrast to previous catalysts, the QE of visible light after 500 nm has been improved to 45.2 % (λ = 500 nm) or 36.4 % (λ = 550 nm). The significant enhancement of HER and NO3− reduction is attributed to the enhanced adsorption of oxygen-containing reactants, the lowering of the reduction overpotential, further enhanced separation efficiency of photogenerated carriers through the ohmic Schottky heterojunction after iron doping. Additionally, the observed capacitor-like nature of 0.1FNP is also an essential factor for the enhanced reduction ability of the composites.

Optimizing Electronic Density at Active W Sites for Boosting Photocatalytic H2 Evolution.

It is highly desirable but challenging to optimize the electronic structure of an active site to realize moderate active site-Hads bond energies for boosting photocatalytic H2 evolution. Herein, an interfacial engineering strategy is developed to simultaneously concentrate hydrogen species and accelerate the combination of an Hads intermediate to generate free H2 by constructing W-WC-W2C (WCC) cocatalysts. Systematic investigations reveal that hybridizing with W2C creates electron-rich W active sites and effectively induces the downshift of the d-band center of W in WC. Consequently, the strong W-Hads bonds on the surface of WC are weakened, thus promoting the desorption of Hads to rapidly produce free H2. The optimized 40-WCC/CdS photocatalyst exhibits a high hydrogen evolution rate of 63.6 mmol g-1 h-1 under visible light (≥420 nm) with an apparent quantum efficiency of 39.5% at 425 nm monochromatic light, which is about 40-fold of the pristine CdS. This work offers insights into the design of cocatalyst for high-efficiency photocatalytic H2 production.

Photothermally driven decoupling of gas evolution at the solid-liquid interface for boosted photocatalytic hydrogen production.

The slow mass transfer, especially the gas evolution process at the solid-liquid interface in photocatalytic water splitting, restricts the overall efficiency of the hydrogen evolution reaction. Here, we report a novel gas-solid photocatalytic reaction system by decoupling hydrogen generation from a traditional solid-liquid interface. The success relies on annealing commercial melamine sponge (AMS) for effective photothermal conversion that leads to rapid water evaporation. The vapor flows towards the photocatalyst covering the surface of the AMS and is split by the catalyst therein. This liquid-gas/gas-solid coupling system avoids the formation of photocatalytic bubbles at the solid-liquid interface, leading to significantly improved mass transfer and conversion. Utilizing CdS nanorods anchored by highly dispersed nickel atoms/clusters as a model photocatalyst, the highest hydrogen evolution rate from water splitting reaches 686.39 μmol h-1, which is 5.31 times that of the traditional solid-liquid-gas triphase system. The solar-to-hydrogen (STH) efficiency can be up to 2.06%. This study provides a new idea for the design and construction of efficient practical photocatalytic systems.

Recent Progress and Challenges in Perylene Small Molecules, Assemblies and Composites for Photocatalytic Hydrogen Evolution

AbstractPerylene diimide (PDI) derivatives are among the best‐known n‐type organic semiconductors because of their unique photophysical and chemical characteristics. In recent years, significant progress has been made in the development of various PDI/composites and their self‐assembled structures for photocatalytic hydrogen (H2) evolution. However, the slow transport of photogenerated charge carriers, rapid charge recombination, limited catalytic activity, and instability of these materials still pose difficulties for their practical use. In order to address these problems, extensive studies have been conducted on structural modifications, molecular design, and synthesis techniques to control the morphology of self‐assembled PDI structures and create new and effective photocatalysts. In this context, perylene based small molecules, their composites with TiO2 and g‐C3N4, self‐assembled perylene derivatives have been designed and their roles as heterogenous photocatalysts for H2 evolution have been investigated thoroughly in literature. In this review, the developments of PDI‐based photocatalysts for H2 evolution are outlined under four different categories. Self‐assembled PDI nanostructures have made the most advancements among all the categories, with highest hydrogen evolution rate (HER) of 61.49 mmol g−1 h−1 while composites composed of perylene derivatives and g‐C3N4 exhibited the second highest rate of hydrogen evolution (17.7 mmol g−1 h−1). This review is intended to give researchers a better understanding and guidelines for designing PDI‐based and other chromophore‐based materials for efficient H2 evolution and their further exploration for future improvement in H2 evolution efficiencies.

Donor-acceptor moiety functionalized covalent organic frameworks for boosting charge separation and H2 photogeneration

Covalent organic frameworks (COFs) have a broad prospect to be used as a photocatalytic platform to convert solar energy into valuable chemicals due to their tunable structures and rich active catalytic sites. However, constructing COFs with tuned sp2-carbon donor-acceptor moiety remains an enormous challenge. Herein, we synthesized two new fully π-conjugated cyano-ethylene-linked COFs containing benzotrithiophene as functional group by Knoevenagel polycondensation reaction. The accetpor 2,2′-bipyridine unit in BTT-BpyDAN-COF skeleton favored the formation of a intermolecular specific electron transport pathway with the donor benzotrithiophene, and thereby promoted charge separation and transfer efficiency. Specifically, a donor-acceptor (D-A) type BTT-BpyDAN-COF exhibited high hydrogen evolution rate of 10.1 mmol g-1h−1 and an excellent apparent quantum efficiency of 4.83 % under visible light irradiation.

Rational design of pyrene and thienyltriazine-based conjugated microporous polymers for high-performance energy storage and visible-light photocatalytic hydrogen evolution from water

Conjugated microporous polymers (CMPs) have found extensive applications in various fields such as optoelectronics, CO2 capture, and catalysis. However, their potential in electrochemical supercapacitors as energy storage and H2 production systems remains relatively unexplored. This limited exploration can be attributed to certain challenges, including issues related to structural and electrochemical stability, as well as the relatively modest specific capacitance. Additionally, many of the CMPs discovered thus far have exhibited lower energy densities, further contributing to this underexplored aspect of their utility. In this study, we prepared two different CMPs [TPET-TTh and PyT-TTh CMPs] containing thienyltriazine units (TTh) for the redox mechanism and constructed electrodes for supercapacitor applications. The synthesized TPET-TTh and PyT-TTh CMPs displayed exceptionally high specific surface areas of 545 and 528 m² g⁻¹, respectively. Furthermore, their pore sizes were very similar, centered at approximately 0.39 and 0.36 nm, respectively. To evaluate their electrochemical properties, the TTh-CMPs were examined using cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The resulting CV curves exhibited rectangular shapes, indicative of the characteristic behavior of electric double-layer capacitors, across a range of potential and scan rates. These TPET-TTh and PyT-TTh CMPs delivered nominal specific capacitances of 74 and 76 F g−1 at 0.5 A g−1, respectively. In addition, they exhibited outstanding capacity retentions of 95.2 and 97.30 % even after 2000 cycles [analyzed at 10 A g−1]. The TTh-CMPs also exhibited excellent light-capture capabilities. The PyT-TTh CMP has faster charge separation and lower charge recombination rates than TPET-TTh CMP. This results in a higher hydrogen evolution rate from the water decomposition reaction. The H2 production rate of PyT-TTh CMP could be as high as 18,533 μmol g−1 h−1, which is approximately 4-fold that of TPET-TTh CMP. This study offers a strategy for the design of TTh-containing CMPs that exhibit exceptional energy storage application and photocatalytic efficiency for H2 evolution.

Oligo(phenylenevinylene)-Based Covalent Organic Frameworks with Kagome Lattice for Boosting Photocatalytic Hydrogen Evolution.

Covalent organic frameworks (COFs) have shown great advantages as photocatalysts for hydrogen evolution. However, the effect of linkage geometry and type of linkage on the extent of π-electron conjugation in the plane of the framework and photocatalytic properties of COFs remains a significant challenge. Herein, two Kagome (kgm) topologic oligo(phenylenevinylene)-based COFs are designed and synthesized for boosting photocatalytic hydrogen evolution via a "two in one" strategy. Under visible light irradiation, COF-954 with 5 wt% Pt as cocatalyst exhibits high hydrogen evolution rate (HER) of 137.23mmol g-1 h-1 , outperforming most reported COF-based photocatalysts. More importantly, even in natural seawater, COF-954 shows an average HER of 191.70mmol g-1 h-1 under ultraviolet-visible (UV-vis) light irradiation. Additionally, the water-drainage experiments indoors and outdoors demonstrate that 25 and 8mL hydrogen gas could be produced in 80 min under UV-vis light and natural sunlight, respectively, corresponding to a high HER of 167.41 and 53.57mmol h-1 g-1 . This work not only demonstrates an effective design strategy toward highly efficient COF-based photocatalysts, but also shows the great potential of using the COF-based photocatalysts for photocatalytic hydrogen evolution.

Direct C-H Arylation Derived Ternary D-A Conjugated Polymers: Effects of Monomer Geometries, D/A Ratios, and Alkyl Side Chains on Photocatalytic Hydrogen Production and Pollutant Degradation.

Donor-acceptor (D-A) conjugated polymer (CP) featuring high charge mobility and widely tunable energy bands have shown promising prospects in photocatalysis. In this work, a library of ternary D-A CPs (22 polymers) based on benzothiadiazole, bithiophene, and fluorene derivatives (i.e., fluorene [Fl], 9,9-dihexylfluorene [HF], and 9,9'-spirobifluorene [SF]) with and without alkyl side chains, and with 3D geometry are designed and synthesized via atom-economical direct C-H arylation polymerization to explore the synergetic effects of stereochemistry, D/A ratio, and alkyl chains on the properties and photocatalytic performances, which reveal that 1) the cross-shaped 3D spirobifluorene (SF) building block shows the highest hydrogen evolution rates (HER) owing to the sufficient photocatalytic active sites exposed, 2) the alkyl-free linear polymer (FlBtBT0.05 ) exhibit the highest photocatalytic pollutant degradation performance owing to its superior charge separation, and 3) the alkyl side chains are redundances that will exert detrimental effects on the aqueous photocatalysis owing to their insulating and hydrophobic property. The structure-property-performance correlation results obtained will provide a desirable guideline for the rational design of CP-based photocatalysts.

Synergistic enhancement of photocatalytic hydrogen evolution by ultrathin oxygen-doped graphitic carbon nitride nanosheets loaded amorphous mesoporous nickel hydroxide

Graphitic carbon nitride (g-C3N4, CN) is widely utilized in the field of photocatalytic hydrogen production owing to its exceptional visible light absorption, addressing the challenge of energy scarcity. However, its development has been hindered by the issue of low charge separation efficiency. In this study, an ultrathin (∼1.65 nm) oxygen-doped graphitic carbon nitride nanosheets loaded amorphous mesoporous nickel hydroxide (a-Ni(OH)2/OCN) photocatalyst was developed through a straightforward calcination and stirring approach. Under visible light irradiation, a-Ni(OH)2/OCN exhibited a remarkably high photocatalytic hydrogen evolution rate of 4764.9 μmol·h−1 g−1, which is 4.7 times greater than that of the original CN. The synergistic effect between O-doping and heterojunction was proved by experimental data analysis combined with DFT calculations. Totally, the introduction of oxygen into CN led to a reduction in its band gap, while a-Ni(OH)2/OCN heterojunction achieved a broaden light absorption range and an effective charge separation due to a type-Ⅱ internal electric fields.

One-pot synthesis of a CdS–MoS2 / CNTs nano-composite for photocatalytic hydrogen production under visible light

The need to meet growing energy demands of global society in a sustainable fashion requires the development of techniques and processes to reduce dependence on fossil fuels and transit to renewable energy sources. Environmentally benign technologies for alternative fuel production in the form of hydrogen can be developed via heterogenous photocatalysis, a process based on utilization of solar energy. To this end, a cadmium sulfide (CdS) based photocatalyst was developed, doped with MoS2 in a one-pot solvothermal synthesis technique, and coupled with multi-walled carbon nanotubes (MWCNTs) as a carbonaceous support. The material exhibiting the highest rate of hydrogen evolution, CM5C3, involved a MWCNTs loading of 3% and MoS2 loading of 5%. Compared to pure CdS synthesized with the same adapted procedure, the 3% CNT loading improved the rate of hydrogen production by nearly 7-fold, and the optimal 5% MoS2 loading further improved the performance by 60%. CM5C3, achieved an apparent quantum efficiency of 7.34%, a 26-fold increase compared to pure CdS. FESEM and HRTEM imaging confirmed the nanorod-like growth of CdS–MoS2 on the CNT surface, with elemental mapping confirming homogenous dispersion of MoS2 and CNTs. In addition, lattice fringe spacings indicated the presence of cubic and hexagonal CdS growing predominantly along the (111) and (002) planes respectively, in addition to MoS2 distributed throughout the crystal lattice. XRD analysis confirmed the presence of hexagonal and cubic CdS, however, MoS2 phases were not registered perhaps due to the low concentration present in the bulk of the material. XPS survey scans showed the presence of C, Cd, Mo, and S only, with trace oxygen impurities. Peak deconvolution indicated the presence of characteristic peaks for CdS and MoS2, in addition to evidence of the presence of Cd–C bonds, indicating strong CdS heterojunctions to the CNT surface.

Ni-BTC-derived CoP-NiCoP/NC microspheres as an efficient catalyst for NaBH4 hydrolysis

The development of a low cost, high performance and stable catalyst is an important prerequisite for the widespread application of efficient hydrogen production from sodium borohydride (NaBH4). Herein, Ni-BTC is derived into CoP-NiCoP/NC catalyst consisting of CoP-NiCoP nanorods and nitrogen-doped carbon (NC) microsphere by hydrothermal and gas-phase phosphorylation methods. The CoP-NiCoP/NC catalyst exhibits good catalytic activity, with a high hydrogen evolution rate of NaBH4 reaching 7052 mL·min−1·g−1 at 303 K, and an activation energy of only 35.57 kJ·mol−1. This is significantly better than most catalysts reported previously. In addition, the CoP-NiCoP/NC catalyst demonstrates good durability with 75 % of the original catalytic activity after 10 performance testing. This excellent catalytic performance is achieved thanks to its porous microsphere structural design and the cooperative effect between CoP and NiCoP. This catalyst with high catalytic performance and mild preparation conditions is promising for future actual applications.

Enhanced visible light photocatalytic hydrogen evolution by Ni cations precise institute S anion in CdS and P ions targeted linking with Ni

Ni directional doping in the lattice of CdSV with the Ni cations targeted linked to P (CdSV-Ni-P) was successfully synthesized via a step wise assembly method, which exhibited an excellent photocatalytic hydrogen production performance. The photoelectric performance characterization proved that the Ni directional doping and Ni cations targeted linked with P in CdSV-Ni-P not only accelerating the photo-generated electrons transfer but also decreasing efficiency of the charge recombination. The density functional theory (DFT) calculations proved that CdSV-Ni-P can also induce more charge-carriers participate in photocatalytic reaction and decrease electron binding restriction capacity. Moreover, the results of UV–vis DR spectra and VB-XPS spectra confirmed that the construction of this CdSV-Ni-P could effectively narrow the bandgap. Meanwhile, the result of Gibbs free energy demonstrated the S-H adsorption bond in CdSV-Ni-P was get weaken, which is benefit for hydrogen desorption from S sites, thus achieving a high hydrogen evolution reaction (HER) result. Based on the synergistic effects, CdSV-Ni6.7-P9.6 presented a relatively high hydrogen evolution rate of 167.5 mmol h-1g−1 under the visible light irradiation (λ ≥ 420 nm), which is almost 60 times of CdSV.

Tuning acceptor content and molecular structure in linear donor–acceptor polymeric photocatalysts for ultrahigh-performance visible-light-driven hydrogen evolution

A series of linear conjugated polymers were synthesized by tuning the dibenzothiophene-S,S-dioxide (DBTO) content and varying their molecular structures, and applied to study the light-driven hydrogen generation from water. We found that the photocatalytic hydrogen evolution rate (HER) under visible light irradiation improved upon increasing the content of DBTO segment in donor–acceptor (D–A) structural polymers. Benefiting from the D–A structure and the high content of active centers of DBTO group, the polymer DB-Th displayed an unprecedentedly high HER of 334.50 mmol g−1h−1 under visible-light-driven and cocatalyst-free conditions (one of the most effective bare polymer photocatalysts that has been reported), which is 1.38-fold as that of the 2D–A type polymer with the lower DBTO content and 255-fold as that of the D–D structural polymer without DBTO segment, demonstrating the significance of acceptor content in D–A structures for achieving ultrahigh photocatalytic hydrogen evolution activity under visible light.

In Situ Growth of CdZnS Nanoparticles@Ti3C2Tx MXene Nanosheet Heterojunctions for Boosted Visible-Light-Driven Photocatalytic Hydrogen Evolution.

Using natural light energy to convert water into hydrogen is of great significance to solving energy shortages and environmental pollution. Due to the rapid recombination of photogenerated carriers after separation, the efficiency of photocatalytic hydrogen production using photocatalysts is usually very low. Here, efficient CdZnS nanoparticles@Ti3C2Tx MXene nanosheet heterojunction photocatalysts have been successfully prepared by a facile in situ growth strategy. Since the CdZnS nanoparticles uniformly covered the Ti3C2Tx Mxene nanosheets, the agglomeration phenomenon of CdZnS nanoparticles could be effectively inhibited, accompanied by increased Schottky barrier sites and an enhanced migration rate of photogenerated carriers. The utilization efficiency of light energy can be improved by inhibiting the recombination of photogenerated electron-hole pairs. As a result, under the visible-light-driven photocatalytic experiments, this composite achieved a high hydrogen evolution rate of 47.1 mmol h-1 g-1, which is much higher than pristine CdZnS and Mxene. The boosted photocatalytic performances can be attributed to the formed heterojunction of CdZnS nanoparticles and Ti3C2Tx MXene nanosheets, as well as the weakened agglomeration effects.

Rationally constructing intercrossed CuInS2 nanosheets on TiO2 nanorods for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting serves as an intriguing strategy for solar energy storage and conversion, but still suffers from the poor efficiency. In this work, a Z-scheme heterostructure comprised of CuInS2 nanosheets and TiO2 nanorods with an intercrossed structure was fabricated. Boosted by the well-matched structure, the as-prepared CuInS2/TiO2 hybrid achieved a high photo-electrocatalytic hydrogen evolution rate of 12.4 µmol/h, which was16 times greater than pure TiO2, owing to more effective solar energy utilization and interfacial photocarrier separation. Furthermore, PEC studies demonstrated that the novel hybrid offered a much higher photocurrent density than the nanoparticle counterpart, which could be ascribed to the elevated separation efficiencies of the photogenerated electron-hole pairs, and accompanied by efficient charge carrier transport. Based on the obtained results, this work provided a potential and promising approach for the fabrication of photo-electrocatalyst, which may inspire additional mechanism research of PEC and photo-electrocatalytic systems with hierarchical architecture.

Zwitterionic and Hydrophilic Vinylene-Linked Covalent Organic Frameworks for Efficient Photocatalytic Hydrogen Evolution.

Developing effective synthetic strategies as well as broadening functionalities for zwitterionic materials that comprise moieties with equimolar cationic and anionic groups still remains a huge challenge. Herein, we develop two zwitterionic vinylene-linked covalent organic frameworks (Zi-VCOF-1 and Zi-VCOF-2) that are a type of novel hydrophilic material. Zi-VCOF-1 and Zi-VCOF-2 are obtained directly through the convenient Knoevenagel condensation of new sulfonic-pyridinium zwitterionic monomers with aromatic aldehyde derivatives. This is the first report on zwitterionic COFs being constructed by the bottom-up functionalization approach from predesigned zwitterionic monomers. Both Zi-VCOFs exhibit a high photocatalytic hydrogen evolution rate (HER) because of their appropriate optical property and outstanding hydrophilicity. Specifically, Zi-VCOF-1 and Zi-VCOF-2 show photocatalytic HER of 13,547 and 5057 μmol h-1 g-1, respectively. Interestingly, the photocatalytic HER of Zi-VCOF-1 is about 2.68 times of that of Zi-VCOF-2, although they differ by only one methyl group in sulfonic-pyridinium zwitterionic pairs. The photocatalytic HER of Zi-VCOF-1 is not only the highest in the vinylene-linked COFs but also outstanding among the most reported COFs. This is the first application of zwitterionic COFs for photocatalytic hydrogen evolution, which would open a new frontier in zwitterionic COFs and be helpful for the design of other photocatalytic materials.

Effects of Ni-flash coating on hydrogen evolution, ad/absorption, and permeation behaviors of advanced high-strength steel during electro-Zn plating

The effects of a thin Ni-flash coating, tens of nanometers thick, on hydrogen evolution, ad/absorption, and permeation of advanced high-strength steel were examined for a deeper understanding of the hydrogen infusion behavior in the steel substrate during electro-Zn plating. The electrochemical permeation technique and impedance spectroscopy were used under cathodic polarization in a step-up manner. In addition to the electrochemical analyses, the hydrogen microprinting technique was employed to identify the distribution of Ag particles (locating hydrogen atoms) in the electro-Zn plated steels with and without a thin intermediate Ni-layer. The results revealed that despite the higher hydrogen evolution rate on Ni-flash coating layer than on bare steel, the intermediate Ni-layer decreased the hydrogen infusion considerably in the steel substrate during electro-Zn plating, due primarily to the lower hydrogen ad/absorption rate on the Ni-flash coating layer, and the predominant hydrogen trapping at the multi-interfacial areas of the Zn-layer/Ni-layer/steel substrate. These results could provide insights into the precise role of a thin (tens of nanometers) Ni-flash coating on the resistance to hydrogen embrittlement of ultra-high-strength steel alloys during electro-Zn plating.

Intermediate Formation of Macrocycles for Efficient Crystallization of 2D Covalent Organic Frameworks with Enhanced Photocatalytic Hydrogen Evolution

AbstractCovalent organic frameworks (COFs) have gained significant attention as key photocatalysts for efficient solar light conversion into hydrogen production. Unfortunately, the harsh synthetic conditions and intricate growth process required to obtain highly crystalline COFs greatly hinder their practical application. Herein, we report a simple strategy for the efficient crystallization of 2D COFs based on the intermediate formation of hexagonal macrocycles. Mechanistic investigation suggests that the use of 2,4,6‐triformyl resorcinol (TFR) as the asymmetrical aldehyde build block allows the equilibration between irreversible enol‐to‐keto tautomerization and dynamic imine bonds to produce the hexagonal β‐ketoenamine‐linked macrocycles, the formation of which could provide COFs with high crystallinity in half hour. We show that COF‐935 with 3 wt % Pt as cocatalyst exhibit a high hydrogen evolution rate of 67.55 mmol g−1 h−1 for water splitting when exposed to visible light. More importantly, COF‐935 exhibits an average hydrogen evolution rate of 19.80 mmol g−1 h−1 even at a low loading of only 0.1 wt % Pt, which is a significant breakthrough in this field. This strategy would provide valuable insights into the design of highly crystalline COFs as efficient organic semiconductor photocatalysts.