Harnessing the Hybridization of a Metal-Organic Framework and Superbase-Derived Ionic Liquid for High-Performance Direct Air Capture of CO2.

Direct air capture (DAC) of CO2 has emerged as the most promising "negative carbon emission" technologies. Despite being state-of-the-art, sorbents deploying alkali hydroxides/amine solutions or amine-modified materials still suffer from unsolved high energy consumption and stability issues. In this work, composite sorbents are crafted by hybridizing a robust metal-organic framework (Ni-MOF) with superbase-derived ionic liquid (SIL), possessing well maintained crystallinity and chemical structures. The low-pressure (0.4 mbar) volumetric CO2 capture assessment and a fixed-bed breakthrough examination with 400 ppm CO2 gas flow reveal high-performance DAC of CO2 (CO2 uptake capacity of up to 0.58 mmol g-1 at 298 K) and exceptional cycling stability. Operando spectroscopy analysis reveals the rapid (400 ppm) CO2 capture kinetics and energy-efficient/fast CO2 releasing behaviors. The theoretical calculation and small-angle X-ray scattering demonstrate that the confinement effect of the MOF cavity enhances the interaction strength of reactive sites in SIL with CO2 , indicating great efficacy of the hybridization. The achievements in this study showcase the exceptional capabilities of SIL-derived sorbents in carbon capture from ambient air in terms of rapid carbon capture kinetics, facile CO2 releasing, and good cycling performance.

Roles of carbon dioxide in the conversion of biomass or waste plastics.

Under the current trend of pursuing sustainable development and environmental protection, the important application of carbon dioxide (CO2) in the conversion process of biomass or waste plastics has become a research direction of concern. The goal of this conversion process is to achieve the efficient use of carbon dioxide, providing a process for the efficient use of biomass, and solving the environmental problems caused by plastics. Remarkable progress has been made in the study of the reaction of CO2 with other substances to produce methane, low-carbon hydrocarbons, methanol, formic acid, and its derivatives, as well as ethers, aldehydes, gasoline, low-carbon alcohols, and other chemicals. In this paper, the important role of CO2 in the conversion of alcohol, sugar, cellulose, and waste plastics was reviewed, with emphasis on the important applications of CO2 as a carbon source, reactant, reaction medium, enhancing agent, solvent, and carrier gas in the conversion of biomass or waste plastics and the basic insights of the reaction mechanism. The emerging CO2 new roles not only put forward the green application of CO2 but also have guiding significance for the utilization of biomass resources and the treatment of waste plastics.

Atomically synergistic Zn-Cr catalyst for iso-stoichiometric co-conversion of ethane and CO2 to ethylene and CO.

Developing atomically synergistic bifunctional catalysts relies on the creation of colocalized active atoms to facilitate distinct elementary steps in catalytic cycles. Herein, we show that the atomically-synergistic binuclear-site catalyst (ABC) consisting of [Formula: see text]-O-Cr6+ on zeolite SSZ-13 displays unique catalytic properties for iso-stoichiometric co-conversion of ethane and CO2. Ethylene selectivity and utilization of converted CO2 can reach 100 % and 99.0% under 500 °C at ethane conversion of 9.6%, respectively. In-situ/ex-situ spectroscopic studies and DFT calculations reveal atomic synergies between acidic Zn and redox Cr sites. [Formula: see text] ([Formula: see text]) sites facilitate ß-C-H bond cleavage in ethane and the formation of Zn-Hδ- hydride, thereby the enhanced basicity promotes CO2 adsorption/activation and prevents ethane C-C bond scission. The redox Cr site accelerates CO2 dissociation by replenishing lattice oxygen and facilitates H2O formation/desorption. This study presents the advantages of the ABC concept, paving the way for the rational design of novel advanced catalysts.

High-Performance CO2 Capture from Air by Harnessing the Power of CaO- and Superbase-Ionic-Liquid-Engineered Sorbents.

Direct air capture (DAC) of CO2 by solid porous materials represents an attractive "negative emission" technology. However, state-of-the-art sorbents based on supported amines still suffer from unsolved high energy consumption and stability issues. Herein, taking clues from the CO2 interaction with superbase-derived ionic liquids (SILs), high-performance and tunable sorbents in DAC of CO2 was developed by harnessing the power of CaO- and SIL-engineered sorbents. Deploying mesoporous silica as the substrate, a thin CaO layer was first introduced to consume the surface-OH groups, and then active sites with different basicities (e. g., triazolate and imidazolate) were introduced as a uniformly distributed thin layer. The as-obtained sorbents displayed high CO2 uptake capacity via volumetric (at 0.4 mbar) and breakthrough test (400 ppm CO2 source), rapid interaction kinetics, facile CO2 releasing, and stable sorption/desorption cycles. Operando diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) analysis under simulated air atmosphere and solid-state NMR under 13 CO2 atmosphere demonstrated the critical roles of the SIL species in low-concentration CO2 capture. The fundamental insights obtained in this work provide guidance on the development of high-performance sorbents in DAC of CO2 by leveraging the combined advantages of porous solid scaffolds and the unique features of CO2 -philic ionic liquids.

In situ fabrication of dynamic self-optimizing Ni3S2 nanosheets as an efficient catalyst for the oxygen evolution reaction.

In this work, a dynamic self-optimizing material consisting of nickel-sulfide nanosheets anchored onto Ni foam (DSO-Ni3S2-NF) as the model material was constructed using a hydrothermal method, and its electrocatalytic performance for oxygen evolution was evaluated. It was found that the electrocatalytic activity of the dynamic self-optimizing (DSO) 25 h-Ni3S2-NF for oxygen evolution is significantly enhanced compared with that of pristine 0 h-Ni3S2-NF since the formed oxide layer evolves into new active sites and the specific process of activity optimization was explored dynamically. The best oxygen evolution reaction (OER) performance was achieved by 25 h-Ni3S2-NF catalyst, which required merely 241 mV overpotential to deliver a current density of 20 mA cm-2, and its Tafel slope was as low as ∼40 mV dec-1, which was superior to most nickel-based catalysts, in 1 M KOH electrolyte. The current density was found to be increased gradually at the same potential and the stability test curves were steady with ignorable decline, showing that the promising strategy of the preparation of a dynamic self-optimizing pre-catalyst may open a new pathway to prepare low-cost, high-performance and stable water splitting catalysts.

2D Fe-doped NiO nanosheets with grain boundary defects for the advanced oxygen evolution reaction.

Two-dimensional (2D) nanomaterials with grain boundary defects are attractive to researchers in many fields, such as energy conversion and storage, sensing, catalysis and biological medicine. In this work, a nanostructure of 2D Fe-doped NiO nanosheets (NiFexO) with grain boundary defects was designed and applied in the electrocatalytic oxygen evolution reaction. This nanomaterial was synthesized through a solvothermal strategy followed by a thermally driven conversion process. In general, NiFexO electrocatalysts were fabricated with gradual morphological variation depending on the atomic ratio of Ni : Fe. It is surprising that the Fe content determines the electrocatalytic performance and the overpotential of water oxidation exhibits an inverted volcanic pattern. As expected, the as-prepared 2D NiFe0.1O nanosheets with grain boundary defects exhibit enhanced OER activity (274 mV@10 mA cm-2) compared with the oxide electrocatalyst reported in 1.0 M KOH owing to the advantages of abundant active sites. This work will shed light on the design and fabrication of novel-structured nanocatalysts.

Hybrid of Fe3C@N, S co-doped carbon nanotubes coated porous carbon derived from metal organic frameworks as an efficient catalyst towards oxygen reduction.

High cost, low reserves and poor stability of the Pt-based catalysts have hindered their large-scale applications. To solve these problems, we develop an efficient method to fabricate a hybrid of Fe3C@N, S co-doped carbon nanotubes coated porous carbon as a superior catalyst towards ORR. The resulted Fe-N-S/C sample exhibits excellent performance in alkaline solution, with a half-wave potential of 0.89 V, which is 30 mV higher than that of commercial Pt/C. The electron transfer number is 3.9 at 0.4 V, indicating a direct four-electron (4e-) pathway towards ORR, and the kinetic current density Jk is 7.96 mA cm-2 at 0.88 V. After 5000 repeated potential cycling test, only 4 mV of down-shift in its half-wave potential was detected, which manifested the remarkable stability of Fe-N-S/C. The electrochemical performance is attributed to the ordered porous structure, high content of active N-species and the synergistic effect between Fe3C group and S dopants.

The in situ etching assisted synthesis of Pt-Fe-Mn ternary alloys with high-index facets as efficient catalysts for electro-oxidation reactions.

Pt-Based alloys enclosed with high-index facets (HIFs) generally show much higher specific catalytic activities than their counterparts with low-index facets in electro-catalytic reactions. However, the exposure of a certain Pt surface would require a well-defined nanostructure, which usually can only be obtained at larger sizes. Therefore, a low dispersion of Pt atoms in Pt-based alloys with HIFs would affect the atomic utilization of Pt, resulting in most of these Pt-based alloys exhibiting lower mass activity than commercial Pt/C and Pt black catalysts for electro-catalytic reactions. Herein, we address a novel strategy to divide the surface areas of larger sized nanocrystals into small surface area nanocrystals by in situ etching Pt-Fe-Mn concave cubes (CNCs) while maintaining the morphology of the Pt-Fe-Mn alloys to improve the utilization of Pt atoms and thus increase the mass activity. Remarkably, the Pt-Fe-Mn unique concave cube (UCNC) nanocrystals (NCs) showed much higher specific and mass activities toward the methanol oxidation reaction (MOR) than the Pt-Fe-Mn CNCs, commercial Pt black and Pt/C. The kinetic analysis from Tafel plots indicated that UCNC Pt-Fe-Mn NCs had the lowest Tafel slope at whole potentials and the splitting of the first C-H bond of a CH3OH molecule with the first electron transfer was the rate-determining step at high potentials (above 0.45 V). In situ Fourier transform infrared reflection (FTIR) spectroscopic investigation at the molecular level indicated that methanol chemical absorption took place at a low potential of -0.2 V at the UCNC NC electrode. Meanwhile, much higher CO2 productivity was observed at the UCNC NC electrode, indicating the strong anti-poisoning ability of the UCNC Pt-Fe-Mn NCs during methanol electrooxidation. Furthermore, in the formic acid oxidation (FAOR) test, the activity and long-term durability of the Pt-Fe-Mn UCNC NCs were also found to be superior to those of the Pt-Fe-Mn CNCs, commercial Pt black and Pt/C. The enhanced catalytic performance in both the MOR and FAOR is most probably due to the unique HIF structure consisting of small sized particles, enhanced Pt utilization, the richness of crystalline defects and synergetic effects of Pt, Fe, and Mn metals. Our present work provides an insight into the rational design of Pt based alloys with HIFs to improve the catalytic performance of electro-catalytic reactions for fundamental study.

Metal-organic frameworks-derived core-shell Fe3O4/Fe3N@graphite carbon nanocomposites as excellent non-precious metal electrocatalyst for oxygen reduction.

Metal-organic frameworks (MOFs), as precursors for synthesizing new carbon materials, hold promise for applications in the oxygen reduction reaction (ORR) as efficient non-precious metal catalysts. Here, a facile template-assisted strategy was adopted to fabricate a core-shell structure derived from MIL-101(Fe) and polyaniline. MIL-101(Fe) nanoparticles obtained by microwave-assisted synthesis were combined with PAni in different ratios and carbonized at 900 °C under flowing N2. An optimized core-shell Fe3O4/Fe3N@graphite carbon structure was successfully prepared and exhibited attractive ORR activity, with a half-wave potential of 0.916 V vs. RHE and an electron transfer number of 4.0 at 0.4 V vs. RHE. Furthermore, the catalyst displayed excellent stability in an alkaline solution. The superior ORR performance of the catalyst is mainly attributed to its stable core-shell structure, large specific surface area and high content of electrocatalytically active N species.