Crystal-Phase and Surface-Structure Engineering of Bi2O3 for Enhanced Electrochemical N2 Fixation to NH3.

The nitrogen reduction reaction (NRR) for ammonia synthesis is hindered by weak N2 adsorption/activation abilities and the hydrogen evolution reaction (HER). In this study, αBi2O3 (monoclinic) and ßBi2O3 (tetragonal) were first synthesized by calcination at different temperatures. Experiments and calculations revealed the effects of Bi2O3 with different crystal phases on N2 adsorption/activation abilities and HER. Then, αBi2O3-x and ßBi2O3-x series catalysts with surface oxygen vacancies (OVs) and Bi0 active sites were synthesized through the partial in situ reduction method. The results demonstrate the following: (I) Tetragonal ßBi2O3 can better adsorb N2 and cleave the N≡N bond, thereby obtaining a lower NRR rate-limiting energy barrier (*N≡N → *N≡N-H, 0.51 eV). Meanwhile, ßBi2O3 can effectively suppress HER by limiting proton adsorption (H+ + e- → *H, 0.54 eV). Therefore, ßBi2O3-x series catalysts exhibit higher NH3 yield and FE than αBi2O3-x. Meanwhile, in situ FTIR further confirms that ßBi2O3 could better adsorb/activate N2, and the NRR distal mechanism occurs on the Bi2O3 surface. (II) The introduction of NaBH4 promotes the conversion of part of Bi3+ on the Bi2O3 surface into Bi0 and releases OVs. The additional active sites (OVs and Bi0) enhance the overall catalyst's adsorption/activation capacity for N2, further increasing the NH3 yield and FE. Meanwhile, semimetal Bi0 can effectively limit electron accessibility, thereby inhibiting the combination of charges and adsorbed protons, reducing the HER reaction and improving the FE of NRR. Therefore, the introduction of NaBH4 effectively improved the NH3 yield and FE of the αBi2O3-x and ßBi2O3-x series catalysts. After optimization, the ßBi2O3-0.6 catalyst has the best NRR performance (NH3 yield: 51.36 µg h-1 mg-1cat.; FE: 38.67%), which is superior to the majority of bismuth-based NRR catalysts. This work not only studies the effects of Bi2O3 with different crystal phases on N2 and HER reaction but also effectively regulates the active components of Bi2O3 surface, thereby realizing efficient NRR to NH3 reaction, which provide valuable insights for the rational design of Bi-based NRR electrocatalysts.

Hydrocarbon Extraction with Ionic Liquids.

Separation and reaction processes are key components employed in the modern chemical industry, and the former accounts for the majority of the energy consumption therein. In particular, hydrocarbon separation and purification processes, such as aromatics extraction, desulfurization, and denitrification, are challenging in petroleum refinement, an industrial cornerstone that provides raw materials for products used in human activities. The major technical shortcomings in solvent extraction are volatile solvent loss, product entrainment leading to secondary pollution, low separation efficiency, and high regeneration energy consumption due to the use of traditional organic solvents with high boiling points as extraction agents. Ionic liquids (ILs), a class of designable functional solvents or materials, have been widely used in chemical separation processes to replace conventional organic solvents after nearly 30 years of rapid development. Herein, we provide a systematic and comprehensive review of the state-of-the-art progress in ILs in the field of extractive hydrocarbon separation (i.e., aromatics extraction, desulfurization, and denitrification) including (i) molecular thermodynamic models of IL systems that enable rapid large-scale screening of IL candidates and phase equilibrium prediction of extraction processes; (ii) structure-property relationships between anionic and cationic structures of ILs and their separation performance (i.e., selectivity and distribution coefficients); (iii) IL-related extractive separation mechanisms (e.g., the magnitude, strength, and sites of intermolecular interactions depending on the separation system and IL structure); and (iv) process simulation and design of IL-related extraction at the industrial scale based on validated thermodynamic models. In short, this Review provides an easy-to-read exhaustive reference on IL-related extractive separation of hydrocarbon mixtures from the multiscale perspective of molecules, thermodynamics, and processes. It also extends to progress in IL analogs, deep eutectic solvents (DESs) in this research area, and discusses the current challenges faced by ILs in related separation fields as well as future directions and opportunities.

Boosting Electrocatalytic N2 Reduction to NH3 by Enhancing N2 Activation via Interaction between Au Nanoparticles and MIL-101(Fe) in Neutral Electrolytes.

Electrocatalytic nitrogen reduction reaction (NRR) has attracted much attention as a sustainable ammonia production technology, but it needs further exploration due to its slow kinetics and the existence of competitive side reactions. In this research, xAu/MIL-101(Fe) catalysts were obtained by loading gold nanoparticles (Au NPs) onto MIL-101(Fe) using a one-step reduction strategy. Herein, MIL-101(Fe), with high specific surface area and strong N2 adsorption capacity, is used as a support to disperse Au NPs to increase the electrochemical active surface area. Au NPs, with a high NRR activity, is introduced as the active site to promote charge transfer and intermediate formation rates. More importantly, the strong interaction between Au NPs and MIL-101(Fe) enhances the electron transfer between Au NPs and MIL-101(Fe), thereby enhancing the activation of N2 and achieving efficient NRR. Among the prepared catalysts, 15 %Au/MIL-101(Fe) has the highest NH3 yield of 46.37 µg h-1 mg-1 cat and a Faraday efficiency of 39.38 % at -0.4 V (vs. RHE). In-situ FTIR reveals that the NRR mechanism of 15 %Au/MIL-101(Fe) follows the binding alternating pathway and also indicates that the interaction between Au NPs and MIL-101(Fe) strengthens the activation of the N≡N bond in the rate-limiting process, thereby accelerating the NRR process.

Environmental Sustainability of π-Electron Donor-Based Deep Eutectic Solvents for Toluene Absorption: A Life-Cycle Perspective.

The novel π-electron donor-based deep eutectic solvents (DESs) have been shown to be a promising type of absorbent with excellent performance on toluene absorption. However, their greenness or sustainability is still unclear. Thus, to bridge the gap and give a comprehensive evaluation for their industrialization potential, the life cycle assessment (LCA) was used to evaluate the potential environmental impacts incurred from their production and usage for absorbing toluene. The environmental profiles are also compared with that of popular choline chloride (ChCl) based DES, common organic solvent triethylene glycol (TEG) and ionic liquid ([EMIM][Tf2 N]). The results indicate that among the involved hydrogen bond acceptors (HBAs), TEBAC generally imparts lower environmental impacts than other HBAs but has higher impacts than ChCl. Although TEBAC-PhOH is not the most environmentally friendly absorbent during the production stage, its outstanding absorption performance minimizes the environmental impact when absorbing the same mass of toluene. Furthermore, the environmental impacts of the toluene absorption process using TEBAC-PhOH is significantly lower than that of [EMIM][Tf2 N], slightly lower than TEG. Therefore, considering both absorption performance and environmental impacts, TEBAC-PhOH can be used as a promising "green and sustainable" toluene absorbent to traditional absorbents and ionic liquids.

Mechanistic insight into the effect of active site motif structures on direct oxidation of methane to methanol over Cu-ZSM-5.

Direct oxidation of methane to methanol (DMTM), a highly challenging reaction in C1 chemistry, has attracted lots of attention. Herein, we investigate the continuous H2O-mediated N2O-DMTM over a series of Cu-ZSM-5-n zeolites prepared by a solid-state ion-exchange method. Excellent CH3OH productivity (194.8 µmol gcat-1 h-1) and selectivity (67.1%) can be achieved over Cu-ZSM-5-0.3%, which surpasses most recently reported zeolite catalysts. The effect of the active site motif structure on the reaction was systematically investigated by the combined experimental and theoretical studies. It has been revealed that both the monomeric [Cu]+ and binuclear [Cu]+-[Cu]+ sites function to produce CH3OH, following the radical rebound mechanism, wherein the latter one plays a dominant role due to the synergistic effect of neighboring [Cu]+ that can efficiently reduce the N2O dissociation barrier to generate active oxygen for CH4 oxidation. Microkinetic modeling results further show that the dicopper site possesses a much higher net reaction rate (1.23 × 105 s-1) than the monomeric Cu site (0.962 s-1); moreover, H2O can shift the rate determining step from the CH3OH desorption step to the N2O dissociation step over the dicopper site, thereby efficiently favoring CH3OH production and resisting carbon deposition. Generally, the study in the present work would substantially favor other highly efficient catalyst designs.

Influences and mechanisms of pyrolytic conditions on recycling BTX products from passenger car waste tires.

Pyrolysis is an effective method for waste tire disposal. However, it has rarely been used to recycle specific highly valuable components (such as benzene, toluene, and xylene (BTX)) from tire rubbers, owing to complicated pyrolytic reactions. This study investigated the pyrolysis process of passenger-car-waste-tires (PCWT) with the help of TG-DTG and Py-GC/MS. Based on response surface methodology (RSM), the effect of pyrolytic parameters on the yields of pyrolytic oil and BTX is evaluated. Furthermore, the BTX generation mechanisms are discussed from the perspective of aliphatic and aromatic hydrocarbon transformations. Additionally, pyrolytic conditions including temperature, rubber particle size, pressure, and gas flow rate were systemically investigated and the optimum pyrolytic condition for yield of BTX (26.5 g per 100 g tire rubber) was obtained [765 K, 0.7 mm, 0.52 MPa and 2.5 mL (g min)-1]. Therein, yield of benzene, toluene and xylene were 1.07, 5.03 and 20.40 g per 100 g tire rubber, respectively. During PCWT pyrolysis, BTX is primarily obtained via the Diels-Alder reactions of small-chain alkenes and transformations of limonene and aromatics. This study elucidates the BTX generation mechanisms during PCWT pyrolysis and clarifies the effects of varying pyrolytic conditions on BTX generation.

Mesoscale study of crystal-plane effects of Ni catalysts on CO2 hydrogenation.

Crystal-plane effects have pivotal roles in the design of catalysts. In this study, a branched Ni (Ni-BN) catalyst was mainly exposed at the Ni(322) surface and was synthesized in the presence of H2. A Ni nanoparticle (Ni-NP) catalyst was mainly exposed at Ni(111) and Ni(100) surfaces and was synthesized without H2. The Ni-BN catalyst showed higher CO2 conversion and methane selectivity than the Ni-NP catalyst. DRIFTS revealed that, unlike the formate route for methanation over the Ni-BN catalyst, the main methanation pathway over the Ni-NP catalyst was the CO2 direct dissociation route, which revealed that the diversity of reaction mechanisms of CO2 methanation on different crystal planes led to the disparity in catalyst activity. DFT calculation of the CO2 hydrogenation reaction over various surfaces showed that the energy barriers on Ni(110) and Ni(322) surfaces were lower than those of Ni(111) and Ni(100) surfaces, which was also related to different pathways of the reaction mechanism. Microkinetic analysis showed the reaction rates on Ni(110) and Ni(322) surfaces were higher than those of other surfaces, and CH4 was the main product on all calculated surfaces, whereas the yields of CO on Ni(111) and Ni(100) surfaces were higher. Kinetic Monte Carlo simulations revealed that the Ni(322) surface with stepped sites was responsible for CH4 generation, and that simulated methane selectivity was consistent with experimental results. The crystal-plane effects of the two morphologies of Ni nanocrystals explained why the reaction activity of the Ni-BN catalyst was greater than that of the Ni-NP catalyst.

Collaborative Purification of Tert-Butanol and N2O over Fe/Co-Zeolite Catalysts.

N2O is a greenhouse gas and a candidate oxidant. Volatile organic pollutants (VOCs) have caused great harm to the atmospheric ecological environment. Developing the technique utilizing N2O as the oxidant to oxidize VOCs to realize the collaborative purification has significant importance and practical value for N2O emission control and VOC abatement. Therefore, the study of N2O catalytic oxidation of tert-butanol based on zeolite catalysts was carried out. A series of molecular sieves, including FER, MOR, ZSM-5, Y, and BEA, were selected as the catalyst objects, and the 1.5% wt Fe and Co were, respectively, loaded on the zeolite catalysts via the impregnation method. It was found that the catalytic performance of BEA was the best among the molecular sieves. Comparing the catalytic performance of Fe-BEA under different load gradients (0.25~2%), it was found that 1.5% Fe-BEA possessed the best catalytic activity. A series of characterization methods showed that Fe3+ content in 1.5% Fe-BEA was the highest, and more active sites formed to promote the catalytic reaction. The α-O in the reaction eventually oxidized tert-butanol to CO2 over the active site. The Co mainly existed in the form of Co2+ cations over Co-BEA samples; the 2% Co-BEA possessing higher amounts of Co2+ exhibited the highest activity among the prepared Co-BEA samples.

Formation Mechanism of Monocyclic Aromatic Hydrocarbons during Pyrolysis of Styrene Butadiene Rubber in Waste Passenger Car Tires.

The production of aromatic hydrocarbons from the waste tire pyrolysis attracts more and more attention because of its tremendous potential. Based on styrene-butadiene rubber (SBR), which is the main rubber in the waste passenger car tires, this work studies the temperature influence on primary pyrolysis product distribution by experimental techniques (Py-GC/MS, TG-MS), and then, the formation mechanism of monocyclic aromatic hydrocarbons (MAHs) observed in the experiment was analyzed by first-principles calculations. The experimental results show that the MAHs during the pyrolysis mainly include styrene, toluene, and xylene, and subsequent calculations showed that these compounds were formed through a series of primary and secondary reactions. The formation pathways of these typical MAHs were studied via the reaction energy barrier analysis, respectively. It shows that the MAHs were not only derived from the benzene ring in the SBR chain but also generated from short-chain alkenes through the Diels-Alder reaction. The obtained pyrolysis reaction mechanism provides theoretical guidance for the regulation of the pyrolysis product distribution of MAHs.

Effective absorption of dichloromethane using deep eutectic solvents.

Chlorinated volatile organic compounds (VOCs), of which dichloromethane (DCM) has become one of the main components because of its extensive use and strong volatility, are recognized as extremely hazardous and refractory pollutants in the atmosphere. The efficient treatment of DCM is of great significance to the protection of environment and human health. In this work, the strategy of DCM capture with deep eutectic solvents (DESs) with different hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) was proposed and systematically investigated. The experimental results show that tetrabutylphosphonium chloride: levulinic acid ([P4444][Cl]-LEV) presents the most excellent DCM absorption capacity among all DESs studied and considerable capacity in [P4444][Cl]-LEV (1:2) with 899 mg DCM/g DES (5.58 mol DCM/mol DES) at 30 °C and DCM partial pressure of 0.3 bar can be achieved. The microscopic absorption mechanism is explored by 1HNMR and FT-IR spectra as well as quantum chemistry calculations, indicating that the absorption is a physical process. The interaction energy analysis suggests that the greater the interaction energy between DES and DCM, the greater the saturated absorption capacity of DCM. The hydrogen bond (HB) contributes most to the weak interaction between DCM and HBA/HBD, and both HBA and HBD play an important role in the absorption of DCM.

Defective UiO-66-NH2 Functionalized with Stable Superoxide Radicals toward Electrocatalytic Nitrogen Reduction with High Faradaic Efficiency.

The electrocatalytic nitrogen reduction reaction (NRR) to NH3 is limited by low Faradaic efficiency (FE). Herein, defective UiO-66-NH2 functionalized with quite stable superoxide radicals (O2•) is developed as a highly active NRR catalyst. The experimental and computational results show that one linker per Zr6 node is missed and two Zr atoms are exposed in the defective UiO-66-NH2. One of the two exposed Zr atoms can stably adsorb O2•, and thus, a Zr-OO• site forms during the preparations without light excitation or postoxidation, while the other Zr atom is activated as an active site. The synergistic effects of the two Zr sites in the defective UiO-66-NH2 suppress hydrogen and hydrazine evolutions considerably. They are as follows: (i) due to repulsion of the proton on the active Zr site and stabilization of the proton on the Zr-OO• site, the active Zr site is unfavorable for the adsorption of the proton with a high energy barrier, which is the HER rate-determining step (RDS); (ii) under the assistance of the OO• of the Zr-OO• site, the first hydrogenation step of *N2 (i.e., NRR RDS) on the active Zr site is promoted; and (iii) relying on the assistance of the OO• of the Zr-OO• site, the continuous hydrogenation of *NH2NH2 to produce NH3 on the active Zr site is spontaneously exothermic, whereas its desorption to hydrazine is blocked. Accordingly, an extremely high FE of ∼85.21% has been realized along with a high yield rate of NH3 (∼52.81 µg h-1 mgcat-1). To the best of our knowledge, it is the highest FE that has been achieved in recent years. Radical scavenging treatment of the defective UiO-66-NH2 and detailed investigations of two categories of control samples further verify the favorable effects of the O2• that closely correlates with the missed linkers on the performance of the NRR to NH3. This work opens a new way toward highly efficient NRR catalysts, i.e., stable radical-activating defective metal-organic frameworks.

Study of passenger-car-waste-tire pyrolysis: Behavior and mechanism under kinetical regime.

The pyrolysis of passenger-car-waste-tires (PCWT) has recently attracted widespread attention because it is a highly effective disposal method. However, a comprehensive understanding of real tire pyrolytic processes is limited owing to the complicated PCWT pyrolysis reaction system, particularly regarding the reaction mechanism. This study investigated the PCWT pyrolytic processes using a thermogravimetric analyzer coupled with mass spectrometry and analyzed all the pyrolytic products using pyrolysis-gas chromatography coupled with mass spectrometry. The composition and distribution of the PCWT pyrolytic products were investigated under a kinetic regime to eliminate other influences on the intrinsic reaction. The pyrolytic products mainly consisted of chain and cyclic alkenes, and monocylic aromatics. Importantly, an integral pyrolytic mechanism network for the PCWT was established based on the pyrolysis of single rubbers (natural, styrene butadiene, and butadiene rubbers). The reaction routes for the main products were determined according to the mechanism. Moreover, a kinetic study of the PCWT pyrolysis revealed the activation energy for this complicated reaction system.

Rational Design of Zinc/Zeolite Catalyst: Selective Formation of p-Xylene from Methanol to Aromatics Reaction.

The production of p-xylene from the methanol to aromatics (MTA) reaction is challenging. The catalytic stability, which is inversely proportional to the particle size of the zeolite, is not always compatible with p-xylene selectivity, which is inversely proportional to the external acid sites. In this study, based on a nano-sized zeolite, we designed hollow triple-shelled Zn/MFI single crystals using the ultra-dilute liquid-phase growth technique. The obtained composites possessed one ZSM-5 layer (≈30 nm) in the middle and two silicalite-1 layers (≈20 nm) epitaxially grown on two sides of ZSM-5, which exhibited a considerably long lifetime (100 % methanol conversion >40 h) as well as an enhanced shape selectivity of p-xylene (>35 %) with a p-xylene/xylene ratio of ≈90 %. Importantly, using this sandwich-like zeolite structure, we directly imaged the Zn species in the micropores of only the ZSM-5 layer and further determined the specific structure and anchor location of the Zn species.

Nanoarchitectonics of Metal-Organic Frameworks for Capacitive Deionization via Controlled Pyrolyzed Approaches.

Next-generation desalination technologies are needed to meet the increasing demand for clean water. Capacitive deionization (CDI) is a thermodynamically efficient technique to treat non-potable water with relatively low salinity. The salt removal capacity and rate of CDI are highly dependent on the electrode materials, which are preferentially porous to store ions through electrosorption and/or redox reactions. Metal-organic frameworks (MOFs) with "infinite" combinations of transition metals and organic linkers simplify the production of carbonaceous materials often with redox-active components after pyrolysis. MOFs-derived materials show great tunability in both compositions and structures but require further refinement to improve CDI performance. This review article summarizes recent progress in derivatives of MOFs and MOF-like materials used as CDI electrodes, focusing on the structural and compositional material considerations as well as the processing parameters and electrode architectures of the device. Furthermore, the challenges and opportunities associated with this research area are also discussed.

Metal-Organic Frameworks and Metal-Organic Gels for Oxygen Electrocatalysis: Structural and Compositional Considerations.

Increasing demand for sustainable and clean energy is calling for the next-generation energy conversion and storage technologies such as fuel cells, water electrolyzers, CO2 /N2 reduction electrolyzers, metal-air batteries, etc. All these electrochemical processes involve oxygen electrocatalysis. Boosting the intrinsic activity and the active-site density through rational design of metal-organic frameworks (MOFs) and metal-organic gels (MOGs) as precursors represents a new approach toward improving oxygen electrocatalysis efficiency. MOFs/MOGs afford a broad selection of combinations between metal nodes and organic linkers and are known to produce electrocatalysts with high surface areas, variable porosity, and excellent activity after pyrolysis. Some recent studies on MOFs/MOGs for oxygen electrocatalysis and their new perspectives in synthesis, characterization, and performance are discussed. New insights on the structural and compositional design in MOF/MOG-derived oxygen electrocatalysts are summarized. Critical challenges and future research directions are also outlined.

H2 O-Built Proton Transfer Bridge Enhances Continuous Methane Oxidation to Methanol over Cu-BEA Zeolite.

Direct oxidation of methane to methanol (DMTM) is a big challenge in C1 chemistry. We present a continuous N2 O-DMTM investigation by simultaneously introducing 10 vol % H2 O into the reaction system over Cu-BEA zeolites. Combining a D2 O isotopic tracer technique and ab initio molecular dynamics (AIMD) simulation, we for the first time demonstrate that the H2 O molecules can participate in the reaction through a proton transfer route, wherein the H2 O molecules can build a high-speed proton transfer bridge between the generated moieties of CH3 - and OH- over the evolved mono(µ-oxo) dicopper ([Cu-O-Cu]2+ ) active site, thereby pronouncedly boosting the CH3 OH selectivity (3.1→71.6 %), productivity (16.8→242.9 µmol gcat -1 h-1 ) and long-term reaction stability (10→70 h) relative to the scenario of absence of H2 O. Unravelling the proton transfer of H2 O over the dicopper [Cu-O-Cu]2+ site would substantially contribute to highly efficient catalyst designs for the continuous DMTM.

Highly efficient capture of odorous sulfur-based VOCs by ionic liquids.

This study proposes the capture of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) from waste gas using an ionic liquid (IL), namely, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf2N]), and examines the process from a molecular level to the laboratory scale, which is then scaled up to the industrial level. The binding energy and weak interactions between DMS/DMDS and the anion/cation in [EMIM][Tf2N] were investigated using quantum chemistry calculations to identify the capture mechanism at the molecular scale. A thermodynamic model (UNIFAC-Lei) was established by the vapor-liquid equilibrium data of the [EMIM][Tf2N] + DMS/DMDS systems measured at the laboratory scale. The equilibrium and continuous absorption experiments were performed, and the results demonstrated that [EMIM][Tf2N] exhibits a highly efficient capture performance at atmospheric conditions, particularly, absorption capacities (AC) for DMS and DMDS are 189.72 and 212.94 mg g-1, respectively, and partial coefficients (PC) as more reasonable evaluation metrics for those are 0.509 × 10-4 and 6.977 × 10-4 mol kg-1 Pa-1, respectively, at the 100 % breakthrough. Finally, a mathematical model of the strict equilibrium stage was established for process simulations, and the absorption process was conceptually designed at the industrial scale, which could provide a decision-making basis for chemical engineers and designers.

Mechanistic insight into H2-mediated Ni surface diffusion and deposition to form branched Ni nanocrystals: a theoretical study.

Present work systematically investigates the kinetic role played by H2 molecules during Ni surface diffusion and deposition to generate branched Ni nanostructures by employing Density Functional Theory (DFT) calculations and ab initio molecule dynamic (AIMD) simulations, respectively. The Ni surface diffusion results unravel that in comparison to the scenarios of Ni(110) and Ni(100), both the subsurface and surface H hinder the Ni surface diffusion over Ni(111) especially under the surface H coverage of 1.5 ML displaying the lowest Ds values, which greatly favors the trapping of the adatom Ni and subsequent overgrowth along the 111 direction. The Ni deposition simulations by AIMD further suggest that both the H2 molecule (in solution) and surface dissociatively adsorbed atomic H can promote Ni depositions onto Ni(111) and Ni(110) facets in a liquid solution. Moreover, a cooperation effect between H2 molecules and surface atomic H can be clearly observed, which greatly favors Ni depositions. Additionally, in addition to working as the solvent, the liquid C2H5OH can also interact with the Ni(111) surface to produce the surface atomic H, which then favored the Ni deposition. Finally, the Ni deposition rate predicted using the deposition constant (Ddep) was found to be much higher than its surface diffusion rate predicted using Ds for Ni(111) and Ni(110), which quantitatively verified the overgrowth along the 111 and 110 directions to produce the branched Ni nanostructures.

Amorphous Ni-Fe-Se hollow nanospheres electrodeposited on nickel foam as a highly active and bifunctional catalyst for alkaline water splitting.

Developing earth-abundant highly efficient catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is indispensable for the widespread implementation of electrochemical water splitting to store renewable energy. Herein, amorphous bimetallic selenide (Ni-Fe-Se) hollow nanospheres electrodeposited on nickel foam (Ni-Fe-Se/NF) are developed as a bifunctional catalyst for the HER and OER. The HER and OER bifunctional activity of Ni-Fe-Se/NF outperforms those of monometallic Ni-Se/NF and Fe-Se/NF owing to the synergy of Ni and Fe in Ni-Fe-Se/NF. Moreover, the amorphous hollow spherical morphology of Ni-Fe-Se/NF increases the active site density and facilitates the mass transfer of electrolytes and H2/O2 products. Ni-Fe-Se/NF drives a current density of 10 mA cm-2 with an overpotential of ∼85 mV for the HER and 100 mA cm-2 with an overpotential of ∼222 mV for the OER. As the HER and OER bifunctional catalyst, Ni-Fe-Se/NF can split alkaline water with total voltages of ∼1.52 V and ∼1.66 V at 10 mA cm-2 and 100 mA cm-2, respectively, and remain stable over 50 hours of operation in 1 M KOH.

Phase-competition-driven formation of hierarchical FeNiZn-MIL-88B-on-MOF-5 octapods displaying high selectivity for the RWGS reaction.

Hierarchical MIL-88B-on-MOF-5 octapods were synthesized via a mechanism involving phase-competition-driven growth (PCDG). Dramatically different morphologies (nanocubes, octapods, flowers) were also produced by controlling the phase competition between MIL-88B and MOF-5. The octapod MOFs showed a high catalytic performance for the reverse water-gas shift (RWGS) reaction.