In-situ grown ternary metal hydroxides@3D oriented crumpled V2C MXene sheets for improved electrocatalytic oxygen evolution reaction.

High valence multi transition metal hydroxides are greatly enriched with OER redox active sites due to strong synergy of heteroatomic nuclei. The efficiency of these redox active sites could be efficiently improved by coupling with highly conductive substrate. The advanced three-dimensional (3D) architecture and hydrophilic terminal functionalities of MXene (MX) considerably enhance the maximum utilization rate of anchored redox active sites by triggering the direct growth of these at MX substrate. Here-in, the freeze-dried 3D network of crumpled Vanadium-Carbide (V2C) MX sheets regulates the crystallization of in-situ grown NiFeCr multi transition metal hydroxides on MX scaffold through co-precipitation process. The XPS results suggest a synergistic chemical interaction of 3D MX scaffold with NiFeCr that modifies the electronic structure of the composite ensuring reduced charge transfer resistance. Besides, as found in FESEM morphological investigation, the well-dispersed NiFeCr multi-transition metal hydroxides are immobilized on open pores like structure of V2C-MX facilitate thoroughly accessible active sites. As a result, the NiFeCr@3D V2C-MX composite has shown an excellent electrocatalytic activity with an overpotential of 410 mV at a current density of 200 mA cm-2, Tafel slope of 100 mV dec in 1M KOH. Besides, the significant interaction between metallic centers and MXene support prevent detachment or agglomeration of active centers providing maximum interaction with the electrolytic ions, quick ionic OH- transportation, speedy and stable electron transfer channels thus ensure the long-term stability of NV-5MX during 53 h continuous operation of OER. Furthermore, we have utilized a more accurate value of half-cell standard reduction potential of the Hg/HgO electrode in the Nernst equation to represent all test voltages and to determine the overpotential values. In essence, this study features a facile approach for the confined growth of multi transition metal hydroxides in the presence of morphologically unique 3D crumpled V2C MXene architectures. Consequently, the increased OER reaction kinetics and improved stability of the synthesized composites are potentially due to synergistic interplay between well dispersed active sites and the conductive substrate.

Giant Third-Order Nonlinear Response of Mixed Perovskite Nanocrystals.

Mixed (FAPbI3)0.92(MAPbBr3)0.08 perovskite thin films exhibit strong nonlinear optical responses, rendering them promising candidates for applications in photonics and optical communications. In this work, we present a systematic study on the ultrafast third-order nonlinear optical processes in mixed perovskite nanocrystals (NCs) by exploring the generation of third harmonic radiation and giant two-photon absorption-based photoluminescence (PL) when excited by femtosecond laser pulses of a 1030 nm central wavelength. A comparative analysis of the coherent third harmonic generation in the thin-film-containing perovskite nanocrystals has shown a 40× enhancement of the third harmonic signal compared to the signal generated in the pure quartz substrate. The cubic dependence of the third-nonlinear optical response of the (FAPbI3)0.92(MAPbBr3)0.08 perovskites on the intensity of the driving radiation was identified using broadband 38 femtosecond driving pulses. The positive nonlinear refractive index (γ = +1.4 × 10-12 cm2·W-1) is found to play an important role in improving the phase-matching conditions of the interacting pulses by generating a strong third order harmonic. The giant two-photon absorption (TPA)-assisted PL peak was monitored and a blue shift of the PL was obtained in the higher intensity range of the laser pulses, with the absorption coefficient ß estimated to be~+7.0 cm·MW-1 at a 1030 nm laser wavelength.

Investigation and Optimization of Mxene Functionalized Mesoporous Titania Films as Efficient Photoelectrodes.

Three-dimensional mesoporous TiO2 scaffolds of anatase phase possess inherent eximious optical behavior that is beneficial for photoelectrodes used for solar energy conversion applications. In this regard; substantial efforts have been devoted to maximizing the UV and/or visible light absorption efficiency; and suppressing the annihilation of photogenerated charged species; in pristine mesoporous TiO2 structures for improved solar illumination conversion efficiency. This study provides fundamental insights into the use of Mxene functionalized mesoporous TiO2 as a photoelectrode. This novel combination of Mxene functionalized TiO2 electrodes with and without TiCl4 treatment was successfully optimized to intensify the process of photon absorption; charge segregation and photocurrent; resulting in superior photoelectrode performance. The photocurrent measurements of the prepared photoelectrodes were significantly enhanced with increased contents of Mxene due to improved absorption efficiency within the visible region; as verified by UV-Vis absorption spectroscopy. The anatase phase of TiO2 was significantly augmented due to increased contents of Mxene and postdeposition heat treatments; as evidenced by structural analysis. Consequently; an appreciable coverage of well-developed grains on the FTO surface was observed in SEM images. As such; these newly fabricated conductive mesoporous TiO2 photoelectrodes are potential candidates for photoinduced energy conversion and storage applications.