Dry Reforming of Methane on Ni/LaZrO2 Catalyst under External Electric Fields: A Combined First-Principles and Microkinetic Modeling Study.

Dry reforming of methane (DRM) reaction has great potential in reducing the greenhouse effect and solving energy problems. Herein, the DRM reaction mechanism and activity on Ni16/LaZrO2 catalyst under electric fields were comprehensively investigated by combining density functional theory calculations with microkinetic modeling. The results showed that La doping increases the interaction between Ni and ZrO2 by Ni cluster transfer of more electrons. The adsorption strength of species followed the order Ni16/ZrO2 > Ni16/LaZrO2, which is consistent with the results for the d-band center but opposite to the metal-support interaction. The best DRM reaction path on Ni16/LaZrO2 was the CH2-O pathway, which is different from the CH-O pathway on Ni(111) and Ni16/ZrO2. Both positive and negative electric fields of strong and weak metal-support interactions reduced the energy barrier of DRM reaction. Importantly, our results showed that the more dispersed and smaller Ni12/LaZrO2 model by considering the dispersing effect induced by La doping, which displayed very different results from that of Ni16/LaZrO2: reduced the energy barrier for methane decomposition, thereby promoting DRM reaction activity. Microkinetic results showed that the carbon deposition behavior of DRM becomes weaker on Ni16/LaZrO2 due to the suppression of methane decomposition in the presence of La doping compared to Ni16/ZrO2, but the opposite result is obtained on Ni12/LaZrO2. The order of DRM reactivity was Ni16/LaZrO2 < Ni16/ZrO2 < Ni12/LaZrO2, which is consistent with the experiment observations. The conversion of methane and CO2 was higher in positive electric fields than in negative electric fields at low temperatures, but the results were opposite at high temperature. Negative electric fields can improve the carbon deposition resistance of Ni-based catalysts compared to positive electric fields. The degree of rate control analysis showed that CHx* oxidation also plays an important role in the DRM reaction. We envision that this study could provide a deeper understanding for guiding the widespread application of electric field catalysis.

Mechanisms of CH4 activation over oxygen-preadsorbed transition metals by ReaxFF and AIMD simulations.

The chemisorbed oxygen usually promotes the CH bond activation over less active metals like IB group metals but has no effect or even an inhibition effect over more active metals like Pd based on the static electronic structure study. However, the understanding in terms of dynamics knowledge is far from complete. In the present work, methane dissociation on the oxygen-preadsorbed transition metals including Au, Cu, Ni, Pt, and Pd is systemically studied by reactive force field (ReaxFF). The ReaxFF simulation results indicate that CH4 molecules mainly undergo the direct dissociation on Ni, Pt, and Pd surfaces, while undergo the oxygen-assisted dissociation on Au and Cu surfaces. Additionally, the ab initio molecular dynamics (AIMD) simulations with the umbrella sampling are employed to study the free-energy changes of CH4 dissociation, and the results further support the CH4 dissociation pathway during the ReaxFF simulations. The present results based on ReaxFF and AIMD will provide a deeper dynamic understanding of the effects of pre-adsorbed oxygen species on the CH bond activation compared to that of static DFT.

Comparative theoretical study of CO2 activation on clean and potassium-preadsorbed low index surfaces of transition metals.

CONTEXT: The efficient catalysis of CO2 adsorption and activation presents a formidable challenge due to its pronounced thermodynamic stability and kinetic inertia. Previous experiments have left gaps in understanding the promotional effects and underlying mechanism of potassium. In this study, we systematically investigate CO2 adsorption and activation on clean and potassium-preadsorbed low index surfaces of transition metals. Theoretical results reveal a substantial augmentation in CO2 binding strength when potassium is introduced, concomitant with a general reduction in activation energies. Notably, linear correlations are significant on close-packed metal surfaces without and with potassium additive. Through a comprehensive analysis encompassing geometric parameters, electronic structures, and energy decomposition, we discern the physical underpinnings of the potassium effect. This enhancement is primarily ascribed to direct electron transfer and dipole-dipole interactions. Furthermore, we scrutinize the impact of an external electric field, demonstrating that the application of a negative electric field accelerates CO2 activation, mirroring the effects observed with potassium. METHODS: All the periodic density function theory (DFT) calculations were performed by the Vienna Ab Initio Simulation package (VASP). The interaction between nucleus and valence electron was described using the pseudopotentials found in the projector augmented wave method (PAW). Throughout the entire work, the Bayesian error estimation functional (BEEF) was used.

Investigation of the oxygen coverage effect on the direct epoxidation of propylene over copper through DFT calculations.

The direct epoxidation of propylene is one of the most important selective oxidation reactions in industry. The development of high-performance copper-based catalysts is the key to the selective oxidation technology and scientific research of propylene. The mechanism of propylene's partial oxidation catalyzed by Cu(111) under different oxygen coverage conditions was studied using density functional theory calculations and microkinetic modeling. We report here in detail two parallel reaction pathways: dehydrogenation and epoxidation. The transition states and energy distributions of the intermediates and products were calculated. The present results showed that propylene oxide (PO) selectivity was high under low oxygen coverage, and increasing the oxygen coverage would decrease the PO selectivity but increase the PO activity, and there was an inverse relationship between PO selectivity and activity. Increasing oxygen coverage would reduce the energy barrier for the C-O bond formation of C3H5O due to the weaker adsorption strength of C3H5, thus decreasing the PO formation selectivity. On the other hand, increasing oxygen coverage would reduce the energy barrier for the possible reaction steps of propylene epoxidation in general, and thus increasing the catalytic activity. It might be proposed that the active site for propylene epoxidation is the metallic copper or partially oxidized copper in terms of the change of PO formation selectivity with oxygen coverage.

M supported on Al-defective Al2-δO3 (M = Fe, Co, Ni, Cu, Ag, Au) as catalysts for acetylene semi-hydrogenation: a theoretical perspective.

Semi-hydrogenation of acetylene is of great importance for both industry and academia. High prices and limited supplements of noble metals leave room for developing base metal catalysts. Experiments revealed the atomically dispersed Cu supported by Al2O3 with excellent long-term stability and high ethylene selectivity, but the physical nature has rarely been investigated theoretically. DFT calculations and microkinetic modeling revealed that the surface OH species could stabilize Cu1/Al2-δO3 and enhance its catalytic performance. The selectivity of ethylene formation decreases with increasing copper clusters (e.g., Cu1/Al2-δO3> Cu4/Al2-δO3> Cu8/Al2-δO3), meaning that the atomically dispersed copper may be a potential candidate for acetylene semi-hydrogenation. The structures of a series of single site catalysts M1/Al2-δO3 (M = Fe, Co, Ni, Ag, Au) are similar to that of Cu1/Al2-δO3, but their performances in catalyzing acetylene semi-hydrogenation are different. M1/Al2-δO3 (M = Ag, Au) shows higher selectivity than Cu1/Al2-δO3, while M1/Al2-δO3 (M = Fe, Co, Ni) demonstrates a higher turnover frequency (TOF) of ethylene than Cu1/Al2-δO3. Moreover, our results indicate that the Ni1-Cu1/Al2-δO3 alloy shows both high activity and ethylene selectivity. The present results show a compensation between the reactivity and the selectivity, suggesting that alloys of VIIIB metals with IB metals like Ni1-Cu1/Al2-δO3 may be efficient candidate catalysts in acetylene selective hydrogenation.

Theoretical insight into the promotion effect of potassium additive on the water-gas shift reaction over low-coordinated Au catalysts.

CONTEXT: How to elucidate the effect of alkali metal promoters on gold-catalyzed water-gas shift reaction intrinsically remains a challenging, because that the complex synergy effects such as strong metal-support interactions, interfacial effects, and charge transfer of supported metal catalysts makes people difficulty in the understanding the alkali promotion phenomenon in nature. Herein, we report a systematically study of whole water-gas shift reaction mechanism on pure and the K-modified defected-Au(211) (i.e., by removing one surface Au atom from perfect Au(211) and make one model with the Au-Au coordination number is six) by using the microkinetic modeling based on first principles. Our results indicate that the presence of K can increase the adsorption ability of oxygen-containing species via the attractive coulomb interaction, has no significant effect on the adsorption of H species, but inhibits the adsorption of CO due to the steric effect. K promoter stabilizes the water adsorption by ~0.3 eV, which results in one order increasing of whole reaction rate. Interestingly, the strong promotion effect of the K can be assigned to the significant direct space interaction between K and the adsorbate H2O* through the inducted electric field, which can be further confirmed by the posed negative electric field on the unpromoted D-Au(211). Microkinetic modeling results revealed that the carboxyl mechanism is the most likely to occur, redox mechanism is the next one, and the formate mechanism is the least likely to occur. For different kinds of alkali metal additives, the adsorption strength of water molecules gradually weakens from Li to Cs, but Na shows the best promoter behavior at the low temperature. By considering the effect of K contents on the reactivity of water-gas shift reaction, we found that the K with the medium coverage (~0.2~0.3 ML) has the strongest promoting effect. It is expected that the conclusion of this work can be extended to other WGSR catalytic systems like Cu(or Pt). METHODS: All calculations were performed by using the plane-wave based periodic method implemented in Vienna ab initio simulation package (VASP, version 5.4.4), where the ionic cores are described by the projector augmented wave (PAW) method. The exchange and correlation energies were computed using the Perdew, Burke and Ernzerhof functional with the vdw correction (PBE-D3). The transition states (TSs) were searched using the climbing image nudged elastic band (CI-NEB) method. Some electronic structure properties like work function was predicated by the DS-PAW software. Microkinetic simulation was carried out using MKMCXX software.

Relationship between oxide identity and electrocatalytic activity of platinum for ethanol electrooxidation in perchlorate acidic solution.

Water and its dissociated species at the solid‒liquid interface play critical roles in catalytic science; e.g., functions of oxygen species from water dissociation are gradually being recognized. Herein, the relationship between oxide identity (PtOHads, PtOads, and PtO2) and electrocatalytic activity of platinum for ethanol electrooxidation was obtained in perchlorate acidic solution over a wide potential range with an upper potential of 1.5 V (reversible hydrogen electrode, RHE). PtOHads and α-PtO2, rather than PtOads, act as catalytic centers promoting ethanol electrooxidation. This relationship was corroborated on Pt(111), Pt(110), and Pt(100) electrodes, respectively. A reaction mechanism of ethanol electrooxidation was developed with DFT calculations, in which platinum oxides-mediated dehydrogenation and hydrated reaction intermediate, geminal diol, can perfectly explain experimental results, including pH dependence of product selectivity and more active α-PtO2 than PtOHads. This work can be generalized to the oxidation of other substances on other metal/alloy electrodes in energy conversion and electrochemical syntheses.

Unraveling the atomic-level vacancy modulation in Cu9S5 for NIR-driven efficient inhibition of drug-resistant bacteria: Key role of Cu vacancy position.

Cu9S5 possesses high hole concentration and potential superior electrical conductivity as a novel p-type semiconductor, whose biological applications remain largely unexploited. Encouraged by our recent work that Cu9S5 has enzyme-like antibacterial activity in the absence of light, which may further enhance the near infrared (NIR) antibacterial performance. Moreover, vacancy engineering can modulate the electronic structure of the nanomaterials and thus optimize their photocatalytic antibacterial activities. Here, we designed two different atomic arrangements with same VCuSCu vacancies of Cu9S5 nanomaterials (CSC-4 and CSC-3) determined by positron annihilation lifetime spectroscopy (PALS). Aiming at CSC-4 and CSC-3 as a model system, for the first time, we investigated the key role of different copper (Cu) vacancies positions in vacancy engineering toward optimizing the photocatalytic antibacterial properties of the nanomaterials. Combined with the experimental and theoretical approach, CSC-3 exhibited stronger absorption energy of surface adsorbate (LPS and H2O), longer lifetime of photogenerated charge carriers (4.29 ns), and lower reaction active energy (0.76 eV) than those of CSC-4, leading to the generation of abundant ·OH for attaining rapid drug-resistant bacteria killed and wound healed under NIR light irradiation. This work provided a novel insight for the effective inhibition of drug-resistant bacteria infection via vacancy engineering at the atomic-level modulation.

Multilayered Molybdate Microflowers Fabricated by One-Pot Reaction for Efficient Water Splitting.

The development of high-performance, low-cost and rapid-production bifunctional electrocatalysts towards overall water splitting still poses huge challenges. Herein, the authors utilize a facile hydrothermal method to synthesize a novel structure of Co-doped ammonium lanthanum molybdate on Ni foams (Co-ALMO@NF) as self-supported electrocatalysts. Owing to large active surfaces, lattice defect and conductive channel for rapid charge transport, Co-ALMO@NF exhibits good electrocatalytic performances which requires only 349/341 mV to achieve a high current density of 600 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Besides, a low cell voltage of 1.52 V is required to reach the current density of 10 mA cm-2 in alkaline medium along with an excellent long-term stability for two-electrode configurations. Density functional theory calculations are performed to reveal the reaction mechanism on Co-ALMO@NF, which shows that the Mo site is the most favorable ones for HER, while the introduction of Co is beneficial to reduce the adsorption intensity on the surface of Co-ALMO@NF, thus accelerating OER process. This work highlighted the importance of the structural design for self-supporting electrocatalysts.

Multifunctional Electrolyte Additive Enables Highly Reversible Anodes and Enhanced Stable Cathodes for Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (AZIBs) are charming devices for large-scale power grid energy storage because of their characteristics of environment friendliness, low cost, high abundance, and safe operation. However, the inferior reversibility of the anode and the loss of cathode capacity always hinder the application of AZIBs. Herein, we propose a simple multifunctional electrolyte additive, diethylenetriamine (DETA), which can inhibit the formation of zinc dendrites and the occurrence of side reactions on the anode, reconstruct the solvated structure and uniform ion flux in the electrolyte, restrain the dissolution of active materials, and induce the crystal transformation on the cathode concurrently. Molecular dynamics Simulation and density functional theory both verified the extraordinary efficacy of DETA. With the assistance of DETA, the Zn anode gained a life of up to 2000 h, and the cathode with commercial V2O5 retained a capacity of 125.2 mA h g-1 at the 1000th discharge process. From the perspective of practical application, this work can open up the application prospect of AZIBs in large-scale energy storage and provide reference for the subsequent works. The findings will greatly promote the application of AZIBs in large-scale energy storage and provide more inspiration for future research.

Electronic Structure Modulation of Ag2 S by Vacancy Engineering for Efficient Bacterial Infection.

Vacancy engineering can modulate the electronic structure of the material and thus contribute to the formation of coordination unsaturated sites, which makes it easier to act on the substrate. Herein, Ag2 S and Ag2 S-100, which mainly have vacancy associates VAgS and VAgSAg , respectively, are prepared and characterized by positron annihilation spectroscopy. Both experimental and theoretical calculation results indicate that Ag2 S-100 exhibits excellent antibacterial activity due to its appropriate bandgap and stronger bacteria-binding ability, which endow it with a superior antibacterial activity compared to Ag2 S in the absence of light. The in vivo antibacterial experiment using a mouse wound-infection model further confirms that Ag2 S-100 has excellent antibacterial and wound-healing properties. This research provides clues for a deeper understanding of modulating electronic structures through vacancy engineering and develops a strategy for effective treatment of bacterial infections.

Efficient photothermal and photodynamic synergistic antibacterial therapy of Cu7S4 nanosheets regulated by facet engineering.

The surface arrangements of nanomaterials can regulate their electronic structure, which will tune physicochemical properties of materials to various applications. In this study, two Cu7S4 nanosheets with (304) and (224) exposed facets were synthesized, respectively, and their antibacterial activity of different facets for replacing antibiotics to solve seriously drug-resistant bacteria were further measured. Experimental and theoretical computation results unveiled that Cu7S4 with (224) exposed facet exhibited excellent antibacterial activity through synergetic photodynamic and photothermal therapy against Gram-positive Bacillus subtilis, Gram-negative Escherichia coli and drug-resistant Pseudomonas aeruginosa under near-infrared light (808 nm) irradiation. Furthermore, the antibacterial agents strongly inhibit mouse skin infection by drug-resistant Pseudomonas aeruginosa cells. The findings provide an efficient antibacterial strategy and might advance the method of designing and producing highly effective antibacterial nanomaterials through facet engineering.

Metallic S-CoTe with Surface Reconstruction Activated by Electrochemical Oxidation for Oxygen Evolution Catalysis.

Developing highly active electrocatalysts toward oxygen evolution reaction (OER) is critical for the application of water splitting for hydrogen production and can further alleviate the energy crisis problem, but still remaining challenging. Especially, unlocking the catalytic site, in turn, helps design the available catalysts. Herein, the nanorod cobalt telluride with sulfur incorporation grown on a carbon cloth (S-CoTe/CC) as catalysts for OER, which displays extraordinary catalytic activity, is reported. Significantly, the in situ formed CoOOH species on the surface of S-CoTe merited from the structure evolution during the OER process serves as the active species. Furthermore, density functional theory calculations demonstrate that sulfur incorporation can tailor the electronic structure of active species and substantially optimize the free energy, accelerating the OER kinetics. This work provides an in-depth understanding of enhanced OER mechanism through foreign elements incorporating into precatalysts and is beneficial for the guiding design of more efficient catalysts.

First-principles theoretical study on dry reforming of methane over perfect and boron-vacancy-containing h-BN sheet-supported Ni catalysts.

The entire reaction mechanism of the dry reforming of methane (DRM) as well as the competition processes over perfect and boron-vacancy-containing h-BN sheet-supported Ni-catalysts (labeled Ni2/h-BN and Ni2/h-BN-B-D) was studied by density functional theory calculations in the present work. Our calculation results show that B-defected h-BN strongly binds to the Ni2 active sites (i.e., shows a strong metal-support interaction (SMSI) character) due to the better electron transfer between Ni2 sites and the support. It was found that CH4 is easier to activate than molecular CO2. The activation of CO2 occurs on the surface of Ni2/h-BN through a direct route, whereas it is prone to follow a hydrogen-assisted path for Ni2/h-BN-B-D via the COOH* intermediate, and the results show that the oxidant O* is easily formed on the surface of Ni2/h-BN-B-D. It was also found that O* is the main oxidant agent for CHx* intermediates through the CH3-O oxidation mechanism. The reaction kinetic analysis indicated that the reverse water gas shift reaction (RWGS) is much more favorable than DRM (1.30 vs. 1.72 eV) over the Ni2/h-BN system, whereas the RWGS and DRM are comparable on Ni2/h-BN-B-D (1.77 vs. 1.66 eV), suggesting a high DRM activity on Ni2/h-BN-B-D. Moreover, neither methane cracking nor a Boudouard reaction to form C* species is thermodynamically and kinetically unfavorable over Ni2/h-BN-B-D; hence, Ni2/h-BN-B-D has strong resistance to carbon deposition. Compared to Ni(111), both Ni2/h-BN-B-D and Ni2/h-BN show strong resistance to carbon deposition. Our results provide a further mechanistic understanding of the DRM over an Ni-based catalyst through the SMSI characteristic and the SMSI favors strong resistance to carbon deposition.

Selective Oxidation of Propylene on Cu2O(111) and Cu2O(110) Surfaces: A Systematically DFT Study.

Density functional theory calculations with a Hubbard U correction were used to investigate the selective oxidation of propylene on Cu2O(111) and Cu2O(110) surfaces, and the mechanism for the selective oxidation of propylene was discussed. On both surfaces, acrolein can be generated by two H-stripping reactions in the allylic hydrogen stripping path, while propylene oxide (PO), propanal, and acetone can be created through the propylene oxametallacycle intermediates in the epoxidation path. Our calculation results indicated that Cu2O has a high crystal plane-controlled phenomenon for the selective oxidation of propylene. It was found that the formations of propanal and acetone are unfavorable kinetically and acrolein is the main product on the (111) surface. On the (110) surface, the activation barrier of acrolein formation is too high to produce and PO becomes the favored product, which is different from the case of the (111) surface. Moreover, energetic span model analysis was carried out to discuss the selective oxidation of propylene on these two surfaces and confirm the above calculations. The present study can help people to design the proper crystal plane catalyst to get the target product of PO with high selectivity and activity in the selective oxidation of propylene.

Enhanced Synergetic Catalytic Effect of Mo2C/NCNTs@Co Heterostructures in Dye-Sensitized Solar Cells: Fine-Tuned Energy Level Alignment and Efficient Charge Transfer Behavior.

A highly efficient and stable electrocatalyst with the novel heterostructure of Co-embedded and N-doped carbon nanotubes supported Mo2C nanoparticles (Mo2C/NCNTs@Co) is creatively constructed by adopting the one-step metal catalyzed carbonization-nitridation strategy. Systematic characterizations and density functional theory (DFT) calculations reveal the advanced structural and electronic properties of Mo2C/NCNTs@Co heterostructure, in which the Co-embedded and N-doped CNTs with tunable diameters present electron-donating effect and the work function is correspondingly regulated from 4.91 to 4.52 eV, and the size-controlled Mo2C nanoparticles exhibit Pt-like 4d electronic structure and the well matched work function (4.85 eV) with I-/I3- redox couples (4.90 eV). As a result, the conductive NCNTs@Co substrate with fine-tuned energy level alignment accelerates the electron transportation and the electron migration from NCNTs@Co to Mo2C, and the active Mo2C shows high affinity for I3- adsorption and high charge transfer ability for I3- reduction, which reach a decent synergetic catalytic effect in Mo2C/NCNTs@Co heterostructure. The DSSC with Mo2C/NCNTs@Co CE achieves a high photoelectric conversion efficiency of 8.82% and exceptional electrochemical stability with a residual efficiency of 7.95% after continuous illumination of 200 h, better than Pt-based cell. Moreover, the synergistic catalytic mechanism toward I3- reduction is comprehensively studied on the basis of structure-activity correlation and DFT calculations. The advanced heterostructure engineering and electronic modulation provide a new design principle to develop the efficient, stable, and economic hybrid catalysts in relevant electrocatalytic fields.

Sulfur-Deficient Bismuth Sulfide/Nitrogen-Doped Carbon Nanofibers as Advanced Free-Standing Electrode for Asymmetric Supercapacitors.

The use of free-standing carbon-based hybrids plays a crucial role to help fulfil ever-increasing energy storage demands, but is greatly hindered by the limited number of active sites for fast charge adsorption/desorption processes. Herein, an efficient strategy is demonstrated for making defect-rich bismuth sulfides in combination with surface nitrogen-doped carbon nanofibers (dr-Bi2 S3 /S-NCNF) as flexible free-standing electrodes for asymmetric supercapacitors. The dr-Bi2 S3 /S-NCNF composite exhibits superior electrochemical performances with an enhanced specific capacitance of 466 F g-1 at a discharge current density of 1 A g-1 . The high performance of dr-Bi2 S3 /S-NCNF electrodes originates from its hierarchical structure of nitrogen-doped carbon nanofibers with well-anchored defect-rich bismuth sulfides nanostructures. As modeled by density functional theory calculation, the dr-Bi2 S3 /S-NCNF electrodes exhibit a reduced OH- adsorption energy of -3.15 eV, compared with that (-3.06 eV) of defect-free bismuth sulfides/surface nitrogen-doped carbon nanofiber (df-Bi2 S3 /S-NCNF). An asymmetric supercapacitor is further fabricated by utilizing dr-Bi2 S3 /S-NCNF hybrid as the negative electrode and S-NCNF as the positive electrode. This composite exhibits a high energy density of 22.2 Wh kg-1 at a power density of 677.3 W kg-1 . This work demonstrates a feasible strategy to construct advanced metal sulfide-based free-standing electrodes by incorporating defect-rich structures using surface engineering principles.

Strategic Design of Vacancy-Enriched Fe1- xS Nanoparticles Anchored on Fe3C-Encapsulated and N-Doped Carbon Nanotube Hybrids for High-Efficiency Triiodide Reduction in Dye-Sensitized Solar Cells.

A new class of hybrids with the unique electrocatalytic nanoarchitecture of Fe1- xS anchored on Fe3C-encapsulated and N-doped carbon nanotubes (Fe1- xS/Fe3C-NCNTs) is innovatively synthesized through a facile one-step carbonization-sulfurization strategy. The efficient synthetic protocols on phase structure evolution and dynamic decomposition behavior enable the production of the Fe1- xS/Fe3C-NCNT hybrid with advanced structural and electronic properties, in which the Fe vacancy-contained Fe1- xS showed the 3d metallic state electrons and an electroactive Fe in +2/+3 valence, and the electronic structure of the CNT was effectively modulated by the incorporated Fe3C and N, with the work function decreased from 4.85 to 4.63 eV. The meticulous structural, electronic, and compositional control unveils the unusual synergetic catalytic properties for the Fe1- xS/Fe3C-NCNT hybrid when developed as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), in which the Fe3C- and N-incorporated CNTs with reduced work function and increased charge density provide a highway for electron transport and facilitate the electron migration from Fe3C-NCNTs to ultrahigh active Fe1- xS with the electron-donating effect, and the Fe vacancy-enriched Fe1- xS nanoparticles exhibit ultrahigh I3- adsorption and charge-transfer ability. As a consequence, the DSSC based on the Fe1- xS/Fe3C-NCNT CE delivers a high power conversion efficiency of 8.67% and good long-term stability with a remnant efficiency of 8.00% after 168 h of illumination, superior to those of traditional Pt. Furthermore, the possible catalytic mechanism toward I3- reduction is creatively proposed based on the structure-activity correlation. In this work, the structure engineering, electronic modulation, and composition control opens up new possibilities in constructing the novel electrocatalytic nanoarchitecture for highly efficient CEs in DSSCs.

Water dissociation on K2O-pre-adsorbed transition metals: a systematic theoretical study.

It is imperative to regulate O-H bond cleavage on metal surfaces with a pre-adsorbed K2O promoter in heterogeneous catalysis. Density functional theory (DFT) calculations have been performed to explore the adsorption and dissociation of water on K2O-pre-adsorbed transition metal surfaces (Au, Ag, Cu, Ni, Pt, Rh, Ir, Pd, Ru, Co and Fe) as compared with those on clean and K-pre-adsorbed metal surfaces. The calculation results indicate that the presence of K2O species significantly promotes water dissociation and the promoting effect depends on the adsorption strength of K2O, namely, the more strongly K2O binds to the metal surface, the less promoting effect it has on the water O-H bond cleavage. Based on geometrical and electronic analysis, the stronger promoting effect of K2O than K on water dissociation on the given metal surfaces can be attributed to stronger attractive electrostatic interactions between OH and the dissociating H of H2O at the TSs as well as between O of H2O and K of K2O at the ISs on K2O-pre-adsorbed surfaces compared with those on K-pre-covered surfaces. Moreover, the additional hydrogen bond interaction between H and Oad of K2O at the ISs on Cu/Ag/Au and Fe/Co/Ni metals would be responsible for the much greater promoting effect of K2O than K on these metal surfaces, while there is a slightly greater promoting effect of K2O on the remaining metal surfaces. From the above analysis, we expect our studies can provide profound understanding of the nature of the promoting effect of K2O on O-H bond scission.

Solvothermally Controlled Synthesis of Organic-Inorganic Hybrid Nanosheets as Efficient pH-Universal Hydrogen-Evolution Electrocatalysts.

Electrocatalysts with a high efficiency and durability for the hydrogen evolution reaction (HER) hold tremendous promise for next-generation energy conversion. Among the state-of-art catalysts for HER, organic-inorganic hybrid nanosheets exhibit a great potential with the merits of high activity, good durability, and low cost. Nevertheless, there is no general method for the synthesis of binary metal phosphide hybrid nanosheet HER catalysts with a tunable morphology and composition. Herein, we report a facile approach for the synthesis of nanosheets consisting of a binary cobalt nickel phosphide hybrid with a hierarchically porous nanostructures using an oxidation- phosphorization process. The as-optimized hybrid nanosheets annealed at 350 °C yield the highest pH-universal activity with overpotentials of 148, 111, and 173 mV in acidic, alkaline, and neutral media, respectively. Besides the promoted mass diffusion in the hierarchically porous structure, the extraordinary performance can be also attributed to the weakened adsorption of hydrogen as a result of the tunable composition of Co and Ni, which was revealed by first-principles calculations.