Separate Active Sites Research Articles

Synergy of oxygen doping and nitrogen vacancy for promoting photocatalytic hydrogen generation of g-C3N4

Photocatalytic hydrogen (H2) generation is a promising and renewable solution to address the energy crisis, but is currently hindered by the limited carrier separation and deficient active sites of photocatalysts. In this study, oxygen (O) doping and nitrogen (N) vacancy co-modified hollow tubular g-C3N4 (O-CN-NV) is successfully prepared to enhance the photocatalytic H2 production. The incorporation of O doping facilitates the separation of photogenerated carriers within the tubular CN, while the N vacancy acts as the surface active site for capturing the photoinduced electrons. As a result, the photocatalytic H2 generation over O–CN–NV reaches 339.4 μmol g−1 h−1 under visible light irradiation, which is 6.1 times higher than that of bulk g-C3N4 (CN). This unique design holds great promise for the development of high-performance photocatalysts to produce renewable fuels.

A binary dumbbell visible light driven photocatalyst for simultaneous hydrogen production with the selective oxidation of benzyl alcohol to benzaldehyde

Photocatalytic H2 production with selective oxidation of organic moieties in an aqueous medium is a fascinating research area. However, the rational design of photocatalysts and their photocatalytic performance are still inadequate. In this work, we efficiently synthesized the MoS2 tipped CdS nanowires (NWs) photocatalyst using soft templates via the two-step hydrothermal method for efficient H2 production with selective oxidation of benzyl alcohol (BO) under visible light illumination. The optimized MoS2 tipped CdS NWs (20 % MoS2) photocatalyst exhibits the highest photocatalytic H2 production efficiency of 13.55 mmol g−1 h−1 with 99 % selective oxidation of BO, which was 42.34 and 2.21 times greater photocatalytic performance than that of pristine CdS NWs and MoS2/CdS NWs, respectively. The directional loading of MoS2 at the tips of CdS NWs (as compared to nondirectional MoS2 at CdS NWs) is the key factor towards superior H2 production with 99 % selective oxidation of BO and has an inhibitory effect on the photo corrosion of pristine CdS NWs. Therefore, the amazing enhancement in the photocatalytic performance and selectivity of optimized MoS2 tipped CdS NWs (20 % MoS2) photocatalyst is due to the spatial separation of their photoexcited charge carriers through the Schottky junction. Moreover, the unique structure of the MoS2 flower at the tip of 1D CdS NWs offers separate active sites for adsorption and surface reactions such as H2 production at the MoS2 flower (confirmed by Pt photo deposition) and subsequently the selective oxidation of BO at the stem of CdS NWs. This rational design of a photocatalyst could be an inspiring work for the further development of an efficient photocatalytic system for H2 production with selective oxidation of BO (a strategy of mashing two potatoes with one fork).

Atomically dispersed Ni active sites on covalent organic frameworks for heterogeneous metallaphotocatalytic C–N cross-coupling

Covalent organic frameworks (COFs) have been acknowledged as a potential platform for heterogeneous photoredox cross-coupling due to their excellent chemical stability, admirable controllability, and extremely prominent surface area. However, synthesizing COFs with bidentate ligand units and utilizing active sites remain a grand challenge. Herein, we report a promising new family of 2,6-pyridinedicarboxaldehyde-bis-(p-aminophenylimine)-based two-dimensional (2D) COFs (PP-COF) using an amine monomer and classic tri-aldehydes. On this basis, dispersed Ni single-atom sites were immobilized on three-types imine-based bi-coordinated 2D COFs (Ni SAS-PP-COF) as heterogeneous dual photoredox catalysts for photo/Ni dual-catalyzed C–N cross-coupling between aryl bromides and alkyl/sulfo amines. Under solar energy irradiation, PP-COF could absorb light to generate electrons and holes, then the photogenerated electrons are transferred to Ni sites to reduce divalent nickel to monovalent nickel. Monovalent nickel is necessary to drive the nickel catalytic cycle. Due to the increased charge separation and abundant active sites, the state-of-the-art Ni SAS-PP-COFs catalyst achieves excellent catalytic performance in comparison of pristine PP-COF. The heterogeneous Ni SAS-PP-COF catalytic system not only confirms the prospect of COFs as potential photoredox/transition-metal dual catalysts, but also provides in-depth insights into the synthesis of functional COFs toward practical metallaphotocatalytic application.

Molecular understanding on ultraviolet photolytic degradation of cyano liquid crystal monomers

Cyano liquid crystal monomers (LCMs) are proposed as emerging chemical pollutants with persistent, bioaccumulative, and toxic properties. Herein, five cyano LCMs, including 4-cyano-4′-ethylbiphenyl (2CB), 4-Butyl-4′-cyanobiphenyl (4CB), 4-cyano-4′-ethoxybiphenyl (2OCB), 4-(trans-4-Ethylcyclohexyl)benzonitrile (2CHB) and 4-(trans-4-Vinylcyclohexyl)benzonitrile (2eCHB), were selected to investigate the reaction kinetics and excited state characteristic variations with their molecular structures by ultraviolet (UV) photolysis. Theoretical calculations reveal that the benzene ring, ethoxy and double bond can deeply alter the electron distribution of cyano LCMs. This will affect the exciton separation ability, excitation properties and active sites to electrophilic attack, causing the distinction in photolysis efficiency. Due to the effective charge separation during local excitation (LE) process and the property of being most susceptible to electrophilic attack by 1O2 and O2•−, 2eCHB with double bond exhibits the largest degradation rate. Conversely, the weakest exciton separation of 2OCB with ethoxy during charge transfer (CT) process limits its subsequent sensitized photolysis process. The molecular orbital and fragment contributions to holes and electrons further deepen the understanding of the excited states charge transfer. This study confirmed that the intrinsic molecular structure, chemical nature and existing sites directly defined the excitation and decomposition activity in the UV photolysis of cyano LCMs.

Mechanism insight into the enhanced photocatalytic purification of antibiotic through encapsulated architectures coupling of crystalline Cu2O/amorphous TiFe layer double hydroxide

Amorphous materials are one of the important candidates for improving heterogeneous photocatalysts because of their unique electronic structures and abundant catalytic sites originating from disorder atomic arrangements. However, there is still much room for the development of new crystalline/amorphous heterogeneous composites for photocatalytic application. Hence efficient synthetic strategies for preparing new crystalline/amorphous heterojunctions are highly desired. Herein, we have realized the deep optimization of photocatalytic activity by fabricating crystalline/amorphous Cu2O/Ti-Fe layer double hydroxide (LDH) heterojunctions. Thanks to the typical Z-scheme mechanism originating from the crystalline/amorphous interfaces, the photocharge separation and catalytic active sites obviously enhance compared to single Cu2O and LDH counterparts. As expected, the photocatalytic removal of tetracycline (TC) of the as-prepared Cu2O/Ti-Fe LDH was over 5.2 and 2.2 times those of the pristine Cu2O nanospheres and Ti-Fe LDH nanosheets. This work illustrates the origin of crystalline Cu2O nanospheres encapsulated in amorphous Ti-Fe layer double hydroxide nanosheets for enhanced photocatalytic activity driven by visible light, and provide a general Cu2O-templated solution-phase synthetic method for the synthesis of novel double-metal layer double hydroxide amorphous nanostructures.

Molecular-level design of isolated molybdenum oxide anchored on carbon nitride for photocatalytic H2 production and environmental remediation

Polymeric carbon nitride typically suffers from sluggish intrinsic charge separation and low available active sites. This paper reports that isolated non-crystalline molybdenum oxide species anchored to N-coordinating cavities (MoCN) have abundant surface-active sites for solid–liquid two-phase reactions, whether for photocatalytic H2 evolution or organic pollutant degradation. Molecular dynamic simulations and density functional theory (DFT) revealed six-fold cavities to stabilize the MoO3 species with non-crystalline features, endowing high dispersion and less aggregation. As proven in single-site heterogeneous catalysts, the photocatalyst benefits from size reduction and accelerated interfacial charge transfer because of its mutual contact between two semiconductors. The MoCN shows a high visible-light H2 evolution of 1265 µmol g−1h−1 under visible light (λ ≥ 400 nm) illumination. The photocatalyst degraded more than 95% tetracycline within 30 min and rhodamine B in 10 min. The MoO3 species confined within π-conjugated systems increase the catalytic contact sites, extending visible light harvesting ability to a longer wavelength. Each single catalytic site facilitates the separation and transfer of charge carriers while interfacial charge still occurs between MoO3 and CN. This molecular-level design and strategy provide a new opportunity and a universal way to extend the boundaries of liquid–solid phase catalysts.

Single-atom Cu anchored on N-doped graphene/carbon nitride heterojunction for enhanced photocatalytic H2O2 production

Photocatalytic production of H2O2 by polymeric carbon nitride has been regarded as a promising approach for the conversion of solar energy into valuable chemicals. However, the efficiency of pristine carbon nitride is limited by the rapid charge recombination and the lack of suitable active sites. Herein, we introduce single-atom Cu anchored on N-doped graphene (Cu-NG) as a cocatalyst coupled with carbon nitride via covalent bonding to enhance photocatalytic H2O2 production. The Cu-NG/carbon nitride could broaden the light absorption from UV to near-infrared region, contributing to the photocatalytic process. Moreover, NG containing electron-rich N atoms could serve as anchoring sites for stabilizing single-atom Cu. Importantly, the single-atom Cu acts not only as an electron sink to steer the interfacial charge separation but also as an active site for molecular oxygen adsorption and activation. With the synergistic effect of the enhanced interfacial charge separation and suitable active sites, Cu-NG/carbon nitride exhibits improved photocatalytic performance with an H2O2 generation rate of 2856 µmol g−1 h−1, which is 2.6 times that of pristine carbon nitride. This work provides a protocol for high-performance photocatalytic H2O2 production using a single-atom cocatalyst.

Aπ-Conjugated Van der Waals Heterostructure Between Single-Atom Ni-Anchored Salphen-Based Covalent Organic Framework and Polymeric Carbon Nitride for High-Efficiency Interfacial Charge Separation.

Semiconductor-based heterostructures have exhibited great promise as a photocatalyst to convert solar energy into sustainable chemical fuels, however, their solar-to-fuel efficiency is largely restricted by insufficient interfacial charge separation and limited catalytically active sites. Here the integration of high-efficiency interfacial charge separation and sufficient single-atom metal active sites in a 2D van der Waals (vdW) heterostructure between ultrathin polymeric carbon nitride (p-CN) and Ni-containing Salphen-based covalent organic framework (Ni-COF) nanosheets is illustrated. The results reveal a NiN2 O2 chemical bonding in NiCOF nanosheets, leading to a highly separated single-atom Ni sites, which will function as the catalytically active sites to boost solar fuel production, as confirmed by X-ray absorption spectra and density functional theory calculations. Using ultrafast femtosecond transient adsorption (fs-TA) spectra, it shows that the vdW p-CN/Ni-COF heterostructure exhibits a faster decay lifetime of the exciton annihilation (τ= 18.3ps) compared to that of neat p-CN (32.6ps), illustrating an efficiently accelerated electron transfer across the vdW heterointerface from p-CN to Ni-COF, which thus allows more active electrons available to participate in the subsequent reduction reactions. The photocatalytic results offer a chemical fuel generation rate of 2.29mmol g-1 h-1 for H2 and 6.2µmol g-1 h-1 for CO, ≈127 and three times higher than that of neat p-CN, respectively. This work provides new insights into the construction of a π-conjugated vdW heterostructure on promoting interfacial charge separation for high-efficiency photocatalysis.

Band engineering of non-metal modified polymeric carbon nitride with broad spectral response for enhancing photocatalytic CO2 reduction

The development of environmentally friendly, low-cost, and efficient catalysts is crucial for photocatalytic CO2 conversion, and polymeric carbon nitride (PCN) is a promising star material for balancing carbon transformation. However, the application of PCN in the field of photocatalytic CO2 reduction is limited by the narrow photoresponse range and slow carrier separation behavior. In this work, a co-polymerization strategy of glycolic acid and urea was adopted to construct a Brown PCN (Bro-PCN) with a Broad spectral response while realizing the introduction of oxygen element which can promote the reconstruction of the electronic structure. The result shows that the Bro-PCN exhibits excellent CO generation performance compared with pristine PCN, even in the spectral range greater than 700 nm, showing the ability to promote the conversion of CO2 to CO. Experimental characterizations and DFT calculation confirmed that the excellent photocatalytic CO2 conversion ability is attributed to the improvement of light absorption and the contribution of added sub-gap impurity states to charge separation behavior and active sites. Thus, this work offers a universal strategy and insights into the design of broad spectral responsive PCN materials in the field of photocatalytic CO2 reduction.

Versatile synthesis of nano-icosapods via cation exchange for effective photocatalytic conversion of biomass-relevant alcohols.

Branched metal chalcogenide nanostructures with well-defined composition and configuration are appealing photocatalysts for solar-driven organic transformations. However, precise design and controlled synthesis of such nanostructures still remain a great challenge. Herein, we report the construction of a variety of highly symmetrical metal sulfides and heterostructured icosapods based on them, in which twenty branches were radially grown in spatially ordered arrangement, with a high degree of structure homogeneity. Impressively, the as-obtained CdS-PdxS icosapods manifest a significantly improved photocatalytic activity for the selective oxidation of biomass-relevant alcohols into corresponding aldehydes coupled with H2 evolution under visible-light irradiation (>420 nm), and the apparent quantum yield of the benzyl alcohol reforming can be achieved as high as 31.4% at 420 nm. The photoreforming process over the CdS-PdxS icosapods is found to be directly triggered by the photogenerated electrons and holes without participation of radicals. The enhanced photocatalytic performance is attributed to the fast charge separation and abundant active sites originating from the well-defined configuration and spatial organization of the components in the branched heterostructures.

Sn (Ⅳ)-doping induced higher lattice strain and activated more lattice oxygen in the Bi2O2CO3 for boosting photocatalytic activity: Experimental and theoratical calculation study

Excellent photocatalysts should poccess satisfactory light utilization, rapid photoinduced carriers separation and aboundant active sites. Herein, a strategy for introducing both compressive strain and oxygen vacancies (OVs) into the Bi2O2CO3 lattice through Sn doping was reported. Results indicated that Sn (Ⅳ) doping induced a stronger compressive strain and more oxygen vacancies were achieved as compared with Sn (II)-doping. Besides, density functional theory (DFT) calculations unvailed that Sn (Ⅳ) doping could optimize energy band structure, reduce the leap energy of electrons, accelerate carriers separation, and improve the reactivity of the active sites. The highly-strained and oxygen-deficient 3 %sn-BOC exhibited enhanced photocatalytic performance with levofloxacin removal of 85 % and Cr (VI) reduction of 98 % within 50 min of illumination, and their reaction rate constants were 4.1 and 4.7 folds higher than that of Bi2O2CO3, respectively, much higher than the counterparts. Moreover, 14 intermediates and 3 possible degradation pathways were proposed, and most of the intermediates were less toxic than LEV. This work shows that simultaneous design of strain engineering and defect engineering via meta doping is a feasible and simple strategy to improve the photocatalytic activity of semiconductors.

DFT–kMC Analysis for Identifying Novel Bimetallic Electrocatalysts for Enhanced NRR Performance by Suppressing HER at Ambient Conditions Via Active-Site Separation

As an alternative to the traditional Haber-Bosch process for ammonia synthesis under high temperature and pressure, the electrochemical nitrogen reduction reaction (NRR) under ambient conditions has been getting attention. Although ruthenium (Ru) is considered the holy-grail catalyst for the NH3 process, it suffers from low selectivity due to the competition between NRR and hydrogen evolution reaction. Experimental screening of new candidate catalysts that can circumvent this challenge is highly resource-intensive, requiring significant labor and expensive precursors. To address this challenge, we have combined density functional theory and kinetic Monte Carlo to shortlist high-performing NRR catalysts. Specifically, this framework utilizes a combination of thermodynamic, electronic, and kinetic analyses to investigate different bimetallic catalysts (i.e., RuTi, RuV2, Ru3W, RuZn3, and RuZr) with specially designed separate active sites for N2 and H adsorption to enhance NRR performance. Our investigations revealed that the newly suggested RuV2 has superior NRR activity with decreased thermodynamic overpotential and increased reaction rates that surpass those of Ru. Notably, RuV2 shows a high N2 selectivity by significantly reducing H poisoning on the catalyst surface and increasing the amount of NH3 with a turnover frequency of 1.1 × 10–4 s–1 under mild conditions (300 K and 1 bar), which is 1 000 times greater than that of a pure Ru electrocatalyst. Given these key observations, we believe our framework can play a pivotal role in elucidating the role of different active sites for NRR and can be extended to other high-impact metallic catalyst families in the future.

High stable photo-Fenton-like catalyst of FeP/Fe single atom-graphene oxide for long-term antibiotic tetracycline removal

The Fenton-like reaction has always suffered from the disadvantages of narrow pH and poor stability. Herein, a Fenton-like catalyst with dual-photo-functional sites of iron phosphide (FeP) and Fe single atom-graphene oxide (Fe1-GO) nanocomposite was constructed to activate H2O2 for antibiotic tetracycline (TC) pollutants removal. Under visible light irradiation, the degradation efficiency of TC reached 100 % within 30 min by FeP/Fe1-GO was 1.36 and 2.32 times than single component of FeP and Fe1-GO. Noteworthy, an extremely long-term stability with 100 times of recycling is achieved and the present system also bear a broad pH range with 3–11. The efficient charge separation and rich Fe single atoms active sites contribute the well Fe3+/Fe2+ cycles to support long-term multiple recycles. Finally, the TC degradation pathway and the toxicity of intermediate products were inferred. This work provides a way to construct high-stable Fenton-like catalyst via dual-photo-functional sites together with single atoms strategy.

Dioxygen Activation and Nδ,Nε-Dihydroxylation Mechanism Involved in the Formation of N-Nitrosourea Pharmacophore in Streptozotocin Catalyzed by Nonheme Diiron Enzyme SznF.

SznF is a nonheme diiron-dependent enzyme that catalyzes the critical N-nitrosation involved in the formation of the N-nitrosourea moiety in the pancreatic cancer drug streptozotocin. The N-nitrosation contains two successive N-hydroxylation and N-nitrosation steps, which are carried out by two separate active sites, namely, the central domain and cupin domain. Recently, the crystal structure of SznF was obtained, and the central domain was proved to contain a diiron cofactor to catalyze the N-hydroxylation. In this work, to gain insights into the O2 activation and the successive N-hydroxylation mechanism, on the basis of the high-resolution crystal structure, the enzyme-substrate complex models were constructed, and a series of combined QM/MM calculations were performed. Based on our calculations, the activation of O2 starts from the diiron(II,III)-superoxo (S) to generate the diiron(IV)-oxo species (Q) via a diiron(III,III)-peroxo (P)-like transition state or unstable intermediate (P'), and species P' can be described as a hybridization of diiron(IV)-oxo species and diiron(III,III)-peroxo (P) owing to the long distances of Fe1-Fe2 (4.22 Å) and O1-O2 (1.89 Å), which is different from those of other nonheme diiron enzymes. In the following hydroxylation of Nδ and Nε, the Nδ-hydroxylation was confirmed to occur first, agreeing with the experimental observations. Because the diiron(IV)-oxo species (Q) is responsible for hydroxylation, the reaction follows the H-abstraction/OH rebound mechanism, and the first abstraction occurs on the Nδ-H rather than Nε-H, which may be attributed to the different orientation of Fe(IV)-oxo relative to N-H as well as the bond dissociation enthalpies of two N-H bonds. The hydroxylation of N-methyl-L-arginine does not employ the diiron(III,III)-hydroperoxo (P″) to trigger the electrophilic attack of the guanidine to directly form the N-O bond, as previously suggested. In addition, our calculations also revealed that the direct attack of the Fe(IV)═O unit to the Nδ of the substrate corresponds to a higher barrier than that in the H-abstraction/OH rebound mechanism. These results may provide useful information for understanding the formation of the di-hydroxylation intermediate involved in the biosynthesis of N-nitrosation.

A ReaxFF study of the effect of pressure on the contribution of char-CO2 gasification to char conversion during pressurized oxy-fuel combustion

The effect of pressure on the contribution of char-CO2 gasification to char conversion during pressurized oxy-fuel combustion (POFC) at 10–25 bar was investigated using reactive force field molecular dynamics (ReaxFF MD) simulation. The results showed that char conversion rates under air (O2/N2), CO2/N2, and oxy-fuel (O2/CO2) atmospheres all increased with the increase of total pressure. Both the char-O2 oxidation under air atmosphere and char-CO2 gasification under CO2/N2 atmosphere followed the Langmuir-Hinshelwood (L-H) mechanism. The char reaction rates calculated by the L-H model based on the assumption of separate active sites and common active sites were compared with the ReaxFF MD simulation results under O2/CO2 atmosphere at different pressures. It was found that char-O2 oxidation competed with char-CO2 gasification under pressure of 10–15 bar, while the competition did not occur under pressure of 20–25 bar. The contribution of char-O2 oxidation and char-CO2 gasification to char conversion during char combustion in O2/CO2 atmosphere were quantitatively determined from the consumption of O2 and CO2. The char-O2 oxidation and char-CO2 gasification rates in O2/CO2 atmosphere at different char conversions were also examined. It indicated that the char-CO2 gasification rate was mainly controlled by the competition between char-CO2 gasification and char-O2 oxidation under low pressures, but was controlled by the partial pressure of CO2 under high pressures.

N-doped porous carbon nanofibers inlaid with hollow Co3O4 nanoparticles as an efficient bifunctional catalyst for rechargeable Li-O2 batteries

Stable and high-efficiency bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are desired for the practical application of Li-O2 batteries with excellent rate performance and cycle stability. Herein, a novel hybrid bifunctional catalyst with carbon nanofibers inlaid with hollow Co3O4 nanoparticles and separate active sites for ORR and OER were prepared and applied in Li-O2 batteries. Benefiting from the synergistic effect of unique porous structural features and high electrocatalytic activity of hollow Co3O4 intimately bound to N-doped carbon nanofibers, the assembled Li-O2 batteries with novel catalyst exhibited high specific capacity, excellent rate capability, and cycle stability up to 150 cycles under a capacity limitation of 500 mAh g−1 at a current density of 100 mA g−1. The facile synthesis and preliminary results in this work show the as-prepared catalyst as a promising bifunctional electrocatalyst for applications in metal-air batteries, fuel cells, and electrocatalysis.

Construction of 2D Zn-MOF/BiVO4 S-scheme heterojunction for efficient photocatalytic CO2 conversion under visible light irradiation

The construction of S-scheme heterojunction photocatalysts has been regarded as an effective avenue to facilitate the conversion of solar energy to fuel. However, there are still considerable challenges with regard to efficient charge transfer, the abundance of catalytic sites, and extended light absorption. Herein, an S-scheme heterojunction of 2D/2D zinc porphyrin-based metal-organic frameworks/BiVO 4 nanosheets (Zn-MOF/BVON) was fabricated for efficient photocatalytic CO 2 conversion. The optimal one shows a 22-fold photoactivity enhancement when compared to the previously reported BiVO 4 nanoflake (ca. 15 nm), and even exhibits ~2-time improvement than the traditional g-C 3 N 4 /BiVO 4 heterojunction. The excellent photoactivities are ascribed to the strengthened S-scheme charge transfer and separation, promoted CO 2 activation by the well-dispersed metal nodes Zn 2 (COO) 4 in the Zn-MOF, and extended visible light response range based on the results of the electrochemical reduction, electron paramagnetic resonance, and in-situ diffuse reflectance infrared Fourier transform spectroscopy. The dimension-matched Zn-MOF/BVON S-scheme heterojunction endowed with highly efficient charge separation and abundant catalytic active sites contributed to the superior CO 2 conversion. This study offers a facile strategy for constructing S-scheme heterojunctions involving porphyrin-based MOFs for solar fuel production. 2D/2D zinc porphyrin-based metal-organic framework (ZnMOF)/BiVO 4 nanosheet S-scheme composites have been successfully constructed with exceptional photoactivity depending on the efficient S-scheme charge transfer and separation, extended visible light response range, and good CO 2 activation by Zn 2 (COO) 4 nodes.

Strategic integration of MoO2 onto Mn0.5Cd0.5S/Cu2O p-n junction: Rational design with efficient charge transfer for boosting photocatalytic hydrogen production

The rational design of durable and nonprecious nanocomposite photocatalysts with efficient charge separation and abundant active sites is still a grand challenge for photocatalytic hydrogen production from water reduction. Herein, a novel ternary nanocomposite, MoO2 decorated Mn0.5Cd0.5S/Cu2O p-n heterojunction has been constructed via a facile two-step route employing the energy band engineering theory. Impressively, the optimized ternary Mn0.5Cd0.5S/Cu2O/MoO2 nanocomposite displays a robust photocatalytic H2-evolution rate of 733.24 μmol h−1 under simulated solar light irradiation, more 4.2 times higher than pure Mn0.5Cd0.5S. The results demonstrated that the p-n heterojunction formed between n-type Mn0.5Cd0.5S and p-type Cu2O could markedly promote the interfacial charge transfer/separation through the internal electric field, whereas the MoO2 cocatalyst with low overpotential could effectively collect photoinduced electrons and dramatically facilitate the H2-evolution kinetics. Moreover, both Cu2O and MoO2 could improve the light-harvesting ability of pristine Mn0.5Cd0.5S, further contributing to the boosted hydrogen generation activity.

Modulating 3d Orbitals of Ni Atoms on Ni‐Pt Edge Sites Enables Highly‐Efficient Alkaline Hydrogen Evolution

AbstractWater electrolysis operating in alkaline environments is a promising route to produce H2 on a massive scale. In this context, designing highly‐active and low‐cost electrocatalysts is of great importance. Here NiPt alloys with plenty of atomically dispersed Pt at the edges to boost hydrogen evolution in alkaline solution are reported. The formed Ni‐Pt atomic pairs at the edges hold engineered electronic structures by reducing the number of coordination atoms to facilitate the kinetically sluggish Volmer step, and further promote the hydrogen coupling step by providing separate active sites as well. With a Pt content of 3at%, this catalyst records an ultralow overpotential of 6 mV to reach the current density of 10 mA cm−2, and delivers a current density of 68.3 mA cm−2 at the overpotential of 30 mV, exceeding that of the commercial 20wt% Pt/C catalyst by a factor of >4. The aberration‐corrected transmission electron microscopy and quasi‐operando X‐ray absorption fine structure measurements show Ni‐Pt atomic pairs serve as active sites and enable the subtle adsorption/desorption balances between various intermediates (OH* and H*) during the hydrogen evolution reaction. The as‐made alloys show high stability with negligible activity decay after a 12 h chronoamperometric test, addressing its feasibility in an overall water‐splitting cell.

Perturbing the Movement of Hydrogens to Delineate and Assign Events in the Reductive Activation and Turnover of Porcine Dihydropyrimidine Dehydrogenase.

The native function of dihydropyrimidine dehydrogenase (DPD) is to reduce the 5,6-vinylic bond of pyrimidines uracil and thymine with electrons obtained from NADPH. NADPH and pyrimidines bind at separate active sites separated by ∼60 Å that are bridged by four Fe4S4 centers. We have shown that DPD undergoes reductive activation, taking up two electrons from NADPH [Beaupre, B. A., et al. (2020) Biochemistry 59, 2419-2431]. pH studies indicate that the rate of turnover is not controlled by the protonation state of the general acid, cysteine 671. The activation of the C671 variants is delineated into two phases particularly at low pH values. Spectral deconvolution of the delineated reductive activation reaction reveals that the initial phase results in the accumulation of charge transfer absorption added to the binding difference spectrum for NADPH. The second phase results in reduction of one of the two flavins. X-ray crystal structure analysis of the C671S variant soaked with NADPH and the slow substrate, thymine, in a low-oxygen atmosphere resolved the presumed activated form of the enzyme that has the FMN cofactor reduced. These data reveal that charge transfer arises from the proximity of the NADPH and FAD bases and that the ensuing flavin is a result of rapid transfer of electrons to the FMN without accumulation of reduced forms of the FAD or Fe4S4 centers. These data suggest that the slow rate of turnover of DPD is governed by the movement of a mobile structural feature that carries the C671 residue.