Computational studies on functionalized Janus MXenes MM'CT2, (M, M' = Zr, Ti, Hf, M ≠ M'; T = -O, -F, -OH): photoelectronic properties and potential photocatalytic activities.

Motivated by the successful synthesis of Janus monolayers of transition metal dichalcogenides (i.e., MoSSe), we computationally investigated the structural, electronic, optical, and transport properties of functionalized Janus MXenes, namely MM'CT2 (M, M' = Zr, Ti, Hf, M ≠ M', T = -O, -F, -OH). The results of the calculations demonstrate that five stable O-terminated Janus MXenes (ZrTiCO2-I, ZrHfCO2-I, ZrHfCO2-III, HfTiCO2-I, and HfTiCO2-III), exhibit modest bandgaps of 1.37-1.94 eV, visible-light absorption (except for ZrHfCO2-I), high carrier mobility, and promising oxidization capability of photoinduced holes. Additionally, their indirect-gap, spatially separated electron-hole pairs, and the dramatic difference between the mobilities of electrons and holes could significantly limit the recombination of photoinduced electron-hole pairs. Our results indicate that the functionalized Janus MXene monolayers are ideal and promising materials for application in visible light-driven photocatalysis.

Synchronous coupling of defects and a heteroatom-doped carbon constraint layer on cobalt sulfides toward boosted oxide electrolysis activities for highly energy-efficient micro-zinc-air batteries.

The sluggish kinetics of oxygen electrocatalysis reactions on cathodes significantly suppresses the energy efficiency of zinc-air batteries (ZABs). Herein, by coupling in situ generated CoS nanoparticles rich in cobalt vacancies (VCo) with a dual-heteroatom-doped layered carbon framework, a hybrid Co-based catalyst (Co1-xS@N/S-C) is designed and synthesized from Co-MOF precursor. Experimental analyses, together with density functional theory (DFT)-based calculations, demonstrate that the facilitated ion diffusion enabled by the introduced VCo, together with the enhanced electron transport benefiting from the well-designed dual-heteroatom-doped laminated carbon framework, synergistically boost the bifunctional electrocatalytic activity of Co1-xS@N/S-C (ΔE = 0.76 V), which is much superior to that of CoS@N/S-C without VCo (ΔE = 0.89 V), CoS without VCo (ΔE = 1.23 V), and the dual-heteroatom-doped laminated carbon framework. As expected, the further assembled ZAB employing Co1-xS@N/S-C as the cathode electrocatalyst exhibits enhanced energy efficiency in terms of better cycling stability (510 cycles/170 hours) and a higher specific capacity (807 mA h g-1). Finally, a flexible/stretched solid state micro-ZAB (F/SmZAB) with Co1-xS@N/S-C as the cathode electrocatalyst and a wave-shaped GaIn-Ni-based liquid metal as the electronic circuit is further designed, which can display excellent electrical properties and long elongation. This work provides a new defect and structure coupling strategy for boosting the oxide electrolysis activities of Co-based catalysts. Furthermore, F/SmZAB represents a promising solution for a compatible micropower source in wearable microelectronics.

Bimetallic ZIF-derived conductive network of Co-Zn@NPC@MWCNT nanocomposites for efficient electromagnetic wave absorption in the whole X-band.

Due to bimetallic MOFs (metal-organic frameworks) possessing diverse structure topologies and superior properties, herein, we used bimetallic ZIFs (zeolitic imidazole frameworks) of MOFs as precursors via the wet chemical and calcination method to fabricate zinc-embellished Co-Zn@NPC@MWCNT nanocomposites with porous conductive carbon-based networks The abundant carbon defects, zinc evaporation, and N-atom doping resulted in the emergence of dipolar/interface polarization, which is good for dielectric loss. The high porosity and large specific surface area were instrumental in the attenuation of multiple scattering and endowed the absorber with an excellent absorption performance. With merely 15 wt% filled loading and 3.187 mm thickness, the obtained composites under the optimized carbonization temperature (800 °C) exhibited double absorption peaks: the RLmin (minimum reflection loss) reached -76.18 dB@12.88 GHz and -33.09 dB@7.76 GHz, respectively. Moreover, a wide absorption bandwidth can be up to 6.56 GHz (7.2-13.76 GHz) with 3.0 mm thickness, distributed in three frequency bands: 20% of the C band, 100% of the X band, and 29.3% of the Ku band. In addition, the conductive network structure of composites was also beneficial for electromagnetic (EM)-wave absorption. An easy preparation process and low cost can further promote the commercial potential of our obtained bimetallic MOF-based material as an EM-wave absorber.