Oxygen-Terminated Nb₂CO₂ MXene with Interfacial Self-Assembled COF as a Bifunctional Catalyst for Durable Zinc–Air Batteries

Abstract

The desirable air cathode in Zn−air batteries (ZABs) that can effectively balance oxygen evolution and oxygen reduction reactions not only needs to adjust the electronic structure of the catalyst but also needs a unique physical structure to cope with the complex gas−liquid environment. In this work, first-principles calculations were carried out to prove that oxygen-terminated Nb 2 CO 2 MXene played an active role in enhancing the sluggish reaction of oxygen intermediates. Nb 2 CO 2 MXene could also stimulate the spatial accumulation of discharge products, which was beneficial to improve the stability of secondary ZABs. Molecular dynamics simulation was used to show that the confinement effect of COF could effectively regulate the concentration of O 2 on the surface of Nb 2 CO 2 @COF, which was conducive to an efficient and durable reaction. COF-LZU1 was self-assembled on the interface of Nb 2 CO 2 MXene (Nb 2 CO 2 @COF) for the first time. The Nb 2 CO 2 @COF electrode had excellent OER/ORR overpotentials with the potential difference (ΔE) of 0.79 V. When applied to the configuration of ZABs, Nb 2 CO 2 @COF showed a power density of 75 mW cm −2 and favorable long-term charge/discharge stability, so it could be used as a potential candidate cathode for noble-metal-based catalysts. This idea of combining MXenes and COFs sheds some light on the design of ZABs.

Ni-Doped Ti3CNTx-Coated Nanoporous Covalent Organic Frameworks to Accelerate Hydrogen Diffusion for Enhanced Hydrogen Evolution

“…The stretching of CH�O occurs at 2920 and 1652 cm −1 . 53,59,60 The appearance of this peak indicates that COF is combined with the oxygen on the surface of Ti 3 CNO 2 . The resultant force of the chemical bond is greater than the van der Waals force, which indicates that the COF material has been firmly attached to the surface of Ni− Ti 3 CNO 2 .…”

“…The peak at 1618 cm –1 and the peak at 3300–3500 cm –1 indicate that they are related to the stretching of NC and N–H in the imine bond of COF, respectively. The stretching of CHO occurs at 2920 and 1652 cm –1 . ,, The appearance of this peak indicates that COF is combined with the oxygen on the surface of Ti 3 CNO 2 . The resultant force of the chemical bond is greater than the van der Waals force, which indicates that the COF material has been firmly attached to the surface of Ni–Ti 3 CNO 2 .…”

“…The grand canonical Monte Carlo (GMMC) method was used to embed 300 hydrogen molecules . The Lennard-Jones (LJ) parameters of each atom under the consistent valence forcefield (CVFF) were obtained through a literature review and our previous work (Table S1, Supporting Information). − The probability density of hydrogen distribution in the Z direction and XY plane was calculated by LAMMPS, and the model was visualized by VMD software. Setting two temperature parameters, 298.15 and 500 K, actually artificially changed the molecular movement speed, thus prolonging the simulation time.…”

Covalent Organic Frameworks (COFs)/MXenes Heterostructures for Electrochemical Energy Storage

“…These active groups are further used as nucleation sites for COF assembly. More specifically, the molecular precursors/primary building blocks of COF are brought together in an ordered manner into a regular pattern/assembly prompted by the covalent/non-covalent molecular interactions manifested between the constituent blocks (Figure c) . In this respect, aminopropyltriethoxysilane (APTES) could be a facile linker moiety that may introduce primary amino terminals as linkage sites for making a further connection with COF precursors.…”

“…As a proof of concept, Zong et al introduced COF/MXene assembly as a non-noble metal-based bifunctional catalytic platform for ZAB air cathode. COF-LZU1 nanoparticles were incorporated onto oxygen-terminated Nb 2 CO 2 to obtain a new and stable MXene nanohybrid (Figure b) . The inclusion of COFs into Nb 2 CT x -based MXene prevents the agglomeration and self-accumulation of individual Nb 2 CT x layers.…”