High yield electrosynthesis of oxygenates from CO using a relay Cu-Ag co-catalyst system.

As a sustainable alternative to fossil fuel-based manufacture of bulk oxygenates, electrochemical synthesis using CO and H2O as raw materials at ambient conditions offers immense appeal. However, the upscaling of the electrosynthesis of oxygenates encounters kinetic bottlenecks arising from the competing hydrogen evolution reaction with the selective production of ethylene. Herein, a catalytic relay system that can perform in tandem CO capture, activation, intermediate transfer and enrichment on a Cu-Ag composite catalyst is used for attaining high yield CO-to-oxygenates electrosynthesis at high current densities. The composite catalyst Cu/30Ag (molar ratio of Cu to Ag is 7:3) enables high efficiency CO-to-oxygenates conversion, attaining a maximum partial current density for oxygenates of 800 mA cm-2 at an applied current density of 1200 mA cm-2, and with 67 % selectivity. The ability to finely control the production of ethylene and oxygenates highlights the principle of efficient catalyst design based on the relay mechanism.

Ion-Conductive Metallo-Covalent Organic Frameworks Constructed with Tridentate Ligand and Zn Nodes.

Metallo-covalent organic frameworks (metallo-COFs) are organometallic scaffolds in which covalently bonded organic frameworks are interwoven with metal-coordinated pendant groups. Unlike the rigid ligands traditionally used for metal coordination, the utilization of "soft" ligands allows for configurable topology and pore structure in metallo-COFs, particularly when the ligands are generated in situ during dynamic synthesis. In this study, we present the rational synthesis of metallo-COFs based on pyridine-2,6-diimine (pdi), wherein the incorporation of Zn2+ ions and in situ-generated tridentate ligands (pdi) yields metallo-COFs with a square-like lattice. In the absence of Zn2+ ions, a topological isomer COF with a Kagome lattice is instead produced. Thus, the presence or absence of Zn2+ ions allows us to switch between two distinct morphologies corresponding to metallo-COF or COF. In comparison to Brønsted acid-catalyzed COF, which necessitates postmetallization for loading metal ions, the metal-templated COF synthesis method yields COFs with improved crystallinity and approximately 1:1 [Zn2+]/ligand composition. Building upon the metal-templated COF synthesis approach, we successfully synthesized pdiCOF-Zn-2 and pdiCOF-Zn-3, which possess square-like and honeycomb lattices, respectively. The enhanced crystallinity and near 1:1 [Zn2+]/ligand composition of pdiCOF-Zn-3 (honeycomb) facilitate its application as ion transport channels.

Hydroiodic-Acid-Initiated Dense yet Porous Ti3 C2 Tx MXene Monoliths toward Superhigh Areal Energy Storage.

The assembly of 3D structured materials from 2D units paves a royal road for building thick and dense electrodes, which are long sought after for practical energy-storage devices. 2D transitional metal carbides (MXene) are promising for this due to their capabilities of solution-based assembly and intrinsic high density, yet face huge challenges in yielding high areal capacitance electrodes owing to the absence of porous ion-transport paths. Here, a gelation-densification process initiated by hydroiodide acids (HI) is proposed, where the protons break the electrostatic balance of MXene nanosheets to trigger gelation, while HI serves as a spacer to prevent nanosheets from restacking during capillary shrinkage. More promising, the controlled evaporation of reductive HI leaves superiorly shrinking yet porous network for ion transport, and the produced monoliths exhibit a high density of 2.74 g cm-3 and an unprecedented areal capacitance of 18.6 F cm-2 .

The Assembly of MXenes from 2D to 3D.

Since their discovery in 2011, transition metal carbides or nitrides (MXenes) have attracted a wide range of attention due to their unique properties and promise for use in a variety of applications. However, the low accessible surface area and poor processability of MXene nanosheets caused by their restacking have severely hindered their practical use, and this is expected to be solved by integrating them into macroscopic assemblies. Here, recent progress in the construction of MXene assemblies from 2D to 3D at the macro and/or microlevel is summarized. The mechanisms of their assembly are also discussed to better understand the relationship between performance and assembled structure. The possible uses of MXene assemblies in energy conversion and storage, electromagnetic interference shielding and absorption, and other applications are summarized.

Fast Gelation of Ti3 C2 Tx MXene Initiated by Metal Ions.

Gelation is an effective way to realize the self-assembly of nanomaterials into different macrostructures, and in a typical use, the gelation of graphene oxide (GO) produces various graphene-based carbon materials with different applications. However, the gelation of MXenes, another important type of 2D materials that have different surface chemistry from GO, is difficult to achieve. Here, the first gelation of MXenes in an aqueous dispersion that is initiated by divalent metal ions is reported, where the strong interaction between these ions and OH groups on the MXene surface plays a key role. Typically, Fe2+ ions are introduced in the MXene dispersion which destroys the electrostatic repulsion force between the MXene nanosheets in the dispersion and acts as linkers to bond the nanosheets together, forming a 3D MXene network. The obtained hydrogel effectively avoids the restacking of the MXene nanosheets and greatly improves their surface utilization, resulting in a high rate performance when used as a supercapacitor electrode (≈226 F g-1 at 1 V s-1 ). It is believed that the gelation of MXenes indicates a new way to build various tunable MXene-based structures and develop different applications.