Layer-by-Layer Assembly of CTAB-rGO-Modified MXene Hybrid Films as Multifunctional Electrodes for Hydrogen Evolution and Oxygen Evolution Reactions, Supercapacitors, and DMFC Applications.

Exceptional electrical conductivity and abundance of surface terminations like-F- and OH- leading to hydrophilicity make the family of 2D transition metal carbides/nitrides and carbonitrides (MXene) excellent candidates for energy storage and conversion applications. MXenes, however, undergo restacking of nanosheets via van der Waals interaction, hindering the active sites, leading to slow electronic and ionic kinetics, and ultimately affecting their electrochemical performance. Herein, we report binder-free cetyltrimethylammonium bromide-reduced graphene oxide (CTAB-rGO)-modified MXene hybrid films on nickel foam as a promising noble metal-free multifunctional electrode synthesized via layer-by-layer assembly and dip coating techniques, which effectively reduce restacking while improving the kinetics. The properties of the as-prepared electrocatalysts are investigated using various physiochemical characterizations and electrochemical measurements to accomplish the objective of "creating one kind of electrocatalyst for multiapplication" with a thorough understanding of the relationship between the material structure, morphology, and electrocatalytic performance. In energy conversion, the synergetic effect of MXene and the CTAB-rGO support helped increase the catalytic activity of the composite for electrochemical water splitting, demonstrating a current density of 10 mA/cm2 at an overpotential (η) of 360 V and a Tafel slope value of 56.6 mV/dec for hydrogen evolution reaction and a current density of 10 mA/cm2 at an overpotential (η) of 179 mV and a Tafel slope value of 47.03 mV/dec for oxygen evolution reaction in an alkaline medium. The electrode material also exhibited a higher oxidation current density (373.60 mA/cm2) compared to that of synthesized MXene toward methanol oxidation reaction in direct methanol fuel cell application. Additionally, the energy storage potential of CTAB-rGO modified MXene as electrode materials for supercapacitors with a high specific capacitance (544.50 F g-1 at 0.5 A g-1) and a good capacity retention of 87% after 5000 cycles was studied. These findings of this work showcase the potential of the electrocatalyst in both conversion and storage of electrochemical energy.

Flower-like Layered NiCu-LDH/MXene Nanocomposites as an Anodic Material for Electrocatalytic Oxidation of Methanol.

Direct methanol fuel cell (DMFC) technology has grabbed much attention from researchers worldwide in the realm of green and renewable energy-generating technologies. Practical applications of DMFCs are marked by the development of highly active, efficient, economical, and long-lasting anode catalysts. Layered double hydroxide (LDH) nanohybrids are found to be efficient electrode materials for methanol oxidation. In this study, we synthesized NiCu-LDH/MXene nanocomposites (NCMs) and investigated their electrochemical performance for methanol oxidation. The formation of NCM was verified through field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), and X-ray photoemission spectroscopy (XPS) analyses. The cyclic voltammetry, chronoamperometry, and electron impedance spectroscopy techniques were carried out to assess the electrocatalytic ability of the methanol oxidation reaction. The incorporation of MXene enhanced the methanol oxidation 2-fold times higher than NiCu-LDH. NCM-45 exhibited high peak current density (86.9 mA cm-2), enhanced electrochemical active surface area (7.625 cm2), and long-term stability (77.8% retention after 500 cycles). The superior performance of NCM can be attributed to the synergistic effect between Ni and Cu and, further, the electronic coupling between LDH and MXene. Based on the results, NCM nanocomposite is an efficient anodic material for the electrocatalytic oxidation of methanol. This study will open the door for the development of various LDH/MXene nanocomposite electrode materials for the application of direct methanol fuel cells.

A comprehensive review on the electrochemical parameters and recent material development of electrochemical water splitting electrocatalysts.

Electrochemical splitting of water is an appealing solution for energy storage and conversion to overcome the reliance on depleting fossil fuel reserves and prevent severe deterioration of the global climate. Though there are several fuel cells, hydrogen (H2) and oxygen (O2) fuel cells have zero carbon emissions, and water is the only by-product. Countless researchers worldwide are working on the fundamentals, i.e. the parameters affecting the electrocatalysis of water splitting and electrocatalysts that could improve the performance of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) and overall simplify the water electrolysis process. Noble metals like platinum for HER and ruthenium and iridium for OER were used earlier; however, being expensive, there are more feasible options than employing these metals for all commercialization. The review discusses the recent developments in metal and metalloid HER and OER electrocatalysts from the s, p and d block elements. The evaluation perspectives for electrocatalysts of electrochemical water splitting are also highlighted.