Controllable Exfoliation of MOF-Derived Van Der Waals Superstructure into Ultrathin 2D B/N Co-Doped Porous Carbon Nanosheets: A Superior Catalyst for Ambient Ammonia Electrosynthesis.

The electrocatalytic nitrogen reduction reaction (NRR) to synthesize NH3 under ambient conditions is a promising alternative route to the conventional Haber-Bosch process, but it is still a great challenge to develop electrocatalysts' high Faraday efficiency and ammonia yield. Herein, a facile and efficient exfoliation strategy to synthesize ultrathin 2D boron and nitrogen co-doped porous carbon nanosheets (B/NC NS) via a metal-organic framework (MOF)-derived van der Waals superstructure, is reported. The results of experiments and theoretical calculations show that the doping of boron and nitrogen can modulate the electronic structure of the adjacent carbon atoms; which thus, promotes the competitive adsorption of nitrogen and reduces the energy required for ammonia synthesis. The B/NC NS exhibits excellent catalytic performance and stability in electrocatalytic NRR, with a yield rate of 153.4 µg·h-1 ·mg-1 cat and a Faraday efficiency of 33.1%, which is better than most of the reported NRR electrocatalysts. The ammonia yield of B/NC NS can maintain 92.7% of the initial NRR activity after 48 h stability test. The authors' controllable exfoliation strategy using MOF-derived van der Waals superstructure can provide a new insight for the synthesis of other 2D materials.

Metal-Organic Framework Derived Ni2P/FeP@NPC Heterojunction as Stability Bifunctional Electrocatalysts for Large Current Density Water Splitting.

The construction of heterojunction has been widely accepted as a prospective strategy for the exploration of non-precious metal-based catalysts that possess high-performance to achieve electrochemical water splitting. Herein, we design and prepare a metal-organic framework derived N, P-doped-carbon-encapsulated Ni2P/FeP nanorod with heterojunction (Ni2P/FeP@NPC) for accelerating the water splitting and working stably at industrially relevant high current densities. Electrochemical results confirmed that Ni2P/FeP@NPC could both accelerate the hydrogen and oxygen evolution reactions. It could substantially expedite the overall water splitting (1.94 V for 100 mA cm-2) which is close to the performance of RuO2 and the Pt/C couple (1.92 V for 100 mA cm-2). In particular, the durability test exhibited that Ni2P/FeP@NPC delivers 500 mA cm-2 without decay after 200 h, demonstrating the great potential for large-scale applications. Furthermore, the density functional theory simulations demonstrated that the heterojunction interface could give rise to the redistribution of electrons, which could not only optimize the adsorption energy of H-containing intermediates to achieve the optimal ΔGH* in a hydrogen evolution reaction, but also reduce the ΔG value in the rate-determining step of an oxygen evolution reaction, thus improving the HER/OER performance.

Self-Terminating Surface Reconstruction Induced by High-Index Facets of Delafossite for Accelerating Ammonia Oxidation Reaction Involving Lattice Oxygen.

Ammonia (NH3 ) is a promising hydrogen (H2 ) carrier for future carbon-free energy systems, due to its high hydrogen content and easiness to be liquefied. Inexpensive and efficient catalysts for ammonia electro-oxidation reaction (AOR) are desired in whole ammonia-based energy systems. In this work, ultrasmall delafossite (CuFeO2 ) polyhedrons with exposed high-index facets are prepared by a one-step NH3 -assisted hydrothermal method, serving as AOR pre-catalysts. The high-index CuFeO2 facet is revealed to facilitate surface reconstruction into active Cu-doped FeOOH nanolayers during AOR processes in ammonia alkaline solutions, which is driven by the favorable Cu leaching and terminates as the 2p levels of internal lattice oxygen change. The reconstructed heterostructures of CuFeO2 and Cu-doped FeOOH effectively activate the dehydrogenation steps of NH3 and exhibit a potential improvement of 260 mV for electrocatalytic AOR at 10 mA cm-2 compared to the pre-restructured phase. Further, density functional theory (DFT) calculations confirm that a lower energy barrier of the rate-determining step (*NH3 to *NH2 ) is presented on high-index CuFeO2 facets covered with Cu-doped FeOOH nanolayers. Innovatively, lattice oxygen atoms in Fe-based oxides and oxyhydroxide are involved in the dehydrogenation steps of AOR as a proton acceptor, broadening the horizons for rational designs of AOR catalysts.

Reticular Coordination Induced Interfacial Interstitial Carbon Atoms on Ni Nanocatalysts for Highly Selective Hydrogenation of Bio-Based Furfural under Facile Conditions.

A rational design of transition metal catalysts to achieve selective hydrogenation of furfural (FFR) to tetrahydrofurfuryl alcohol (THFA) under facile conditions is a promising option. In this work, a series of Ni catalysts were synthesized by controlled thermal treatment of Ni-based metal-organic frameworks (MOFs), with the purpose of modulating the interface of nickel nanoparticles by the reticular coordination in MOF precursors. The catalytic performance indicates that Ni/C catalyst obtained at 400 °C exhibits efficient conversion of FFR (>99%) and high selectivity to THFA (96.1%), under facile conditions (80 °C, 3 MPa H2, 4.0 h). The decomposition of MOF at low temperatures results in highly dispersed Ni0 particles and interfacial charge transfer from metal to interstitial carbon atoms induced by coordination in MOF. The electron-deficient Ni species on the Ni surface results in an electropositive surface of Ni nanoparticles in Ni/C-400, which ameliorates furfural adsorption and enhances the hydrogen heterolysis process, finally achieving facile hydrogenation of FFR to THFA.

Adsorption in Reversed Order of C2 Hydrocarbons on an Ultramicroporous Fluorinated Metal-Organic Framework.

Metal-organic frameworks have been widely studied in the separation of C2 hydrocarbons, which usually preferentially bind unsaturated hydrocarbons with the order of acetylene (C2 H2 )>ethylene (C2 H4 )>ethane (C2 H6 ). Herein, we report an ultramicroporous fluorinated metal-organic framework Zn-FBA (H2 FBA=4,4'-(hexafluoroisopropylidene)bis(benzoic acid)), shows a reversed adsorption order characteristic for C2 hydrocarbons, that the uptake for C2 hydrocarbons of the framework and the binding affinity between the guest molecule and the framework follows the order C2 H6 >C2 H4 >C2 H2 . Density-functional theory calculations confirm that the completely reversed adsorption order behavior is attributed to the close van der Waals interactions and multiple cooperative C-H⋅⋅⋅F hydrogen bonds between the framework and C2 H6 . Moreover, Zn-FBA exhibits a high selectivity of about 2.9 for C2 H6 over C2 H4 at 298 K and 1 bar. The experimental breakthrough studies show that the high-purity C2 H4 can be obtained from C2 H6 and C2 H4 mixtures in one step.

Adsorption Site Selective Occupation Strategy within a Metal-Organic Framework for Highly Efficient Sieving Acetylene from Carbon Dioxide.

The separation of acetylene and carbon dioxide is an essential but challenging process owing to the similar molecular sizes and physical properties of the two gas molecules. Notably, these molecules usually exhibit different orientations in the pore channel. We report an adsorption site selective occupation strategy by taking advantage of differences in orientation to sieve the C2 H2 from CO2 in a judiciously designed amine-functionalized metal-organic framework, termed CPL-1-NH2 . In this material, the incorporation of amino groups not only occupies the adsorption sites of CO2 molecules and shields the interaction of uncoordinated oxygen atom and CO2 molecules resulting in a negligible adsorption amount and a decrease in enthalpy of adsorption but also strengthened the binding affinity toward C2 H2 molecules. This material thus shows an extremely high amount of C2 H2 at low pressure and a remarkably high C2 H2 /CO2 IAST selectivity (119) at 1 bar and 298 K.

Sustained-Release Method for the Directed Synthesis of ZIF-Derived Ultrafine Co-N-C ORR Catalysts with Embedded Co Quantum Dots.

M-N-C catalysts with optimized local and external structures offer great potential for replacing expensive and labile Pt-based catalysts for the oxygen reduction reaction (ORR) in fuel cells. Herein, we report a novel and facile strategy of synthesizing ultrafine ZIF-derived Co-N-C catalysts by precisely controlling the crystallization rate of ZIFs. The employment of meta-soluble Co-doped basic zinc acetate (Co-BZA), which shows a sustained-release effect in solvents, allows for the control of the solubility of Co-BZA in solvents. Detailed investigations suggest that the solubility of Co-BZA in the solvent is the key for governing the grain size of the resulting Zn/Co bimetallic ZIFs. Therefore, the self-assembly process between ligands and metal ions can be regulated by tuning the composition of mixed solvents, thus enabling rational tuning of the grain size of the resulting ZIFs. One-step pyrolysis of the ultrafine Zn/Co bimetallic ZIF precursor leads to Co and N co-doped carbon with an ultrafine grain size (termed UF Co-N-C). The Co centers that are uniformly distributed in the carbon matrix possess a quantum-dot-level grain size. Furthermore, this type of carbon nanohybrid exhibits a hierarchical pore structure, as well as a high surface area. When used as an ORR catalyst, the UF Co-N-C catalyst possesses high ORR activity (with an E1/2 of 0.9 V) that can rival 20 wt % commercial Pt/C (with an E1/2 of 0.835 V) in alkaline media. Notably, this catalyst also displays strong ORR performance similar to that of Pt/C in acidic media. The superior durability and methanol tolerance in both alkaline and acidic media for UF Co-N-C compared to Pt/C illustrate its great potential in replacing commercial Pt/C catalysts. The outstanding ORR performance of UF Co-N-C could be attributed to the simultaneous optimization of both external structures and active sites, demonstrating the effectiveness of this strategy in constructing ORR catalysts with controlled structures and desired functionalities.