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Gamma irradiation-based synthesis and modification of nanomaterials has emerged as a versatile technique to increase the electrochemically active sites for catalytic reactions. Ionizing radiation has a tremendous effect on the optical, electrical, microstructural, and physicomechanical properties of nanomaterials. By controlling the irradiation parameters such as the absorbed dose rate and the total absorbed dose, tunable synthesis and surface modifications can be achieved. Herein, the gamma irradiation technique was used to modify the Ti3C2Tx MXene and the effect on the electrochemical performance of gamma-irradiated Ti3C2Tx (γ-Ti3C2Tx) for the hydrogen evolution reaction (HER) and supercapacitor applications was studied. The irradiated structure was characterized using X-ray diffraction and scanning electron microscopy, which confirmed the formation of γ-Ti3C2Tx MXene. The electrochemical properties were examined by cyclic voltammetry, galvanostatic charge–discharge, and linear sweep voltammetry. The γ-Ti3C2Tx exhibits a specific capacitance of 169 F g−1 at 10 A g−1, with 87% capacitance retention after 5000 charge/discharge cycles. Furthermore, the γ-Ti3C2Tx-300 electrocatalyst shows an overpotential of 478 mV with a Tafel slope of 157 mV dec−1. The enhanced electrochemical properties of the gamma-irradiated MXene electrodes were attributed to quick diffusion pathways enabled by increased d-spacing upon irradiation. [ABSTRACT FROM AUTHOR]

In this study, a honeycomb-like porous-structured nickel–iron–cobalt layered double hydroxide/Ti3C2Tx (NiFeCo–LDH@MXene) composite was successfully fabricated on a three-dimensional nickel foam using a simple hydrothermal approach. Owing to their distinguishable characteristics, the fabricated honeycomb porous-structured NiFeCo–LDH@MXene composites exhibited outstanding bifunctional electrocatalytic activity for pair hydrogen and oxygen evolution reactions in alkaline medium. The developed NiFeCo–LDH@MXene electrocatalyst required low overpotentials of 130 and 34 mV to attain a current density of 10 mA cm−2 for OER and HER, respectively. Furthermore, an assembled NiFeCo–LDH@MXene‖NiFeCo–LDH@MXene device exhibited a cell voltage of 1.41 V for overall water splitting with a robust firmness for over 24 h to reach 10 mA cm−2 current density, signifying outstanding performance for water splitting reactions. These results demonstrated the promising potential of the designed 3D porous NiFeCo–LDH@MXene sheets as outstanding candidates to replace future green energy conversion devices. [ABSTRACT FROM AUTHOR]

Summary: Hydrogen and oxygen evolution through electrochemical water splitting is essential for effective and inexpensive production of hydrogen and oxygen, which depends on the development of economical, and extremely active electrocatalysts. Two‐dimensional (2D) nano‐laminated materials are imperious as electrocatalysts due to their phenomenal properties and extensive scope of applications. In this work, we report a greener way of synthesizing MXene without hydrofluoric acid (HF) treatment and demonstrated its excellent electrochemical characteristics as an overall water‐splitting catalyst. Cl‐terminated MXenes (Ti3C2Cl2) were synthesized via a molten salt approach, in which the MAX phase (Ti3AlC2) was reacted with copper chloride (CuCl2) salt followed by thermal treatment at a temperature of 550°C for 5 hours. The resulting Cl‐terminated MXene was characterized by scanning electron microscopy, X‐ray diffraction, transmission electron microscope, Raman, Fourier transform infrared spectroscopy, energy dispersive X‐ray analysis, X‐ray photoelectron spectroscopy, and electrochemical testing was performed in the alkaline media for oxygen evolution reactions (OER) and hydrogen evolution reactions (HER). For OER in 1 M KOH, Cl‐terminated MXene achieves a benchmark of 30 mA cm−2 current density at an overpotential of 330 mV and a Tafel slope of 48 mV dec−1, while HF‐MXene exhibits an overpotential of 390 mV and a Tafel slope of 136 mV dec−1. For HER, Cl‐MXene attains an overpotential of 259 mV, and a Tafel slope of 92 mV dec−1 to achieve the 10 mA cm−2 current density, on the other hand, HF‐MXene achieves an overpotential of 444 mV and a Tafel slope of 311 mV dec−1. Furthermore, the electrocatalyst exhibited excellent long‐term stability of 0.7 V at 100 mA cm−2 current density for 36 hours. The synthesis methodology for greener Cl‐terminated MXene coupled with an outstanding electrocatalytic activity is set to open new avenues of catalyst design for water splitting. [ABSTRACT FROM AUTHOR]

Summary: The electrochemical water splitting by using renewable electricity is being considered as a sustainable, clean and considerable source of hydrogen fuel for future transportation and energy applications. The sluggish kinetics at anode and cathode, thus, require plenty of research work on the development of an efficient and stable electrocatalyst, which would provide the enhanced activity of water splitting reaction as well as stability for long‐term operation. This review draws a detailed sketch of the progress in the pursuit of replacing noble metals with non‐precious perovskite‐based substitutes without compromising the key electrocatalyst characteristics. Herein, we critically analysed the latest research work and progress of perovskite oxides for anodic/oxygen reduction reaction/cathodic, including the mechanism behind perovskite oxide catalytic reactions, controlled composition as well as the role of various design strategies to achieve high catalytic performance. Moreover, the article also provides an insight to the associated density functional theory that can provide profound understanding of mechanism, involved behind these reactions and, the need for computational studies to exploit the active area of catalysts. It is believed that this article will assist researchers to explore key area of research in the current generation perovskites that show enhanced catalytic performance as well as to work on unforeseen challenges. [ABSTRACT FROM AUTHOR]

Designing electrocatalysts for electrochemical water splitting to generate renewable energy has been a prospective interest throughout the previous decade. The efficiency of electrochemical water splitting, however, is impeded by the sluggish kinetics of the oxygen evolution reaction (OER). Herein, the heterostructure of layered double hydroxides (NiFe-LDH) and MXene (Ti 3 C 2 T x) were synthesized via hydrothermal (NiFe-LDH/Ti 3 C 2 T x -H) and physical mixing (NiFe-LDH/Ti 3 C 2 T x -P) methods. The NiFe-LDH/Ti 3 C 2 T x -H exhibited an overpotential of 269 mV at 10 mA cm−2, indicating superior performance as compared to NiFe-LDH/Ti 3 C 2 T x -P (353 mV) and RuO 2 (313 mV). The double layer capacitance (C dl) of NiFe-LDH/Ti 3 C 2 T x -H was higher (2.05 mF cm−2) as compared to NiFe-LDH/Ti 3 C 2 T x -P (1.63 mF cm−2), thus indicating more active sites for improving reaction kinetics. Additionally, the NiFe-LDH/Ti 3 C 2 T x -H electrocatalyst retained stable performance (96.1%) after 10 h of chronopotentiometry at a constant current density of 10 mA cm−2. [Display omitted] • Synthesized novel NiFe-LDH/Ti 3 C 2 T x -H heterostructure via hydrothermal route. • Uniform growth of NiFe-LDH prevents the agglomeration of NiFe-LDH and Ti 3 C 2 T x. • The strong interfacial interactions enhance the catalytic efficiency. • NiFe-LDH/Ti 3 C 2 T x -H exhibited a lower overpotential of 269 mV at 10 mA cm−2 for OER. [ABSTRACT FROM AUTHOR]

We report a unique composite of La 0.4 Sr 0.4 Ti 0.9 Ni 0.1 O 3-δ (LSTN) nanoparticles interlaced with two dimensional Ti 3 C 2 T x (MXene) nanosheets, providing high conductivity. LSTN heterostructure synthesized by the sol-gel method produces a large oxygen vacancy and creates a variable valence state while, MXene synthesized from Hydrofluoric acid (HF) treatment resulted in a highly hydrophilic and conductive surface, thereby enhancing the charge transferability. For OER, the LSTN/MXene 66.67% electrode exhibits a benchmark of 10 mA cm−2 at a potential of 1.56 (V vs RHE) in 1 M KOH. It has exhibited the lowest Tafel slope of 44 mV dec−1 and highest mass activity (60 mA g−1 @ 1.59 V) due to quicker ions diffusion and increased available exposed area. Moreover, the efficient LSTN/MXene 66.67% electrode showed good long-term durability during a 24 h stability test at a current density of 100 mA cm−2. The strong interfacial interaction and high charge transfer among LSTN nanoparticles and 2D MXene nanosheets not only provide good structural strength to the composite but also improves the redox activity of LSTN/MXene 66.67% catalyst towards OER. This work provides improved conductive properties of perovskite by developing a composite of perovskite and MXene, that has significantly enhanced electrochemical properties of the catalyst by undergoing fast kinetics. [Display omitted] • La 0.4 Sr 0.4 Ti 0.9 Ni 0.1 O 3-δ nanoparticles interlaced within Ti 3 C 2 T x nanosheets. • For OER, the LSTN/MXene 66.67% electrode exhibits 10 mA cm−2 at 1.56 V (E vs RHE). • The LSTN/MXene 66.67% showed good long-term stability during a 24 h test. [ABSTRACT FROM AUTHOR]

MXenes are a family of 2D transition metal carbides, nitrides, and carbonitrides that have surface termination groups such as –OH, –O, and –F. The presence of transition metal imparts conductivity, surface termination groups induce hydrophilicity and layered structure offers large surface area which makes MXenes a potential candidate to be utilized as an electro-catalyst with enhanced efficiency. The Water Electrolysis (WE) efficiency of an electro-catalysts is dependent on the performance of half-cell reactions i.e. Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER). The OER kinetics of most of the bi-functional electrocatalysts are considered sluggish due to which they are tested in alkaline media. However, due to the metallic nature and surface properties of MXenes, they as substrate not only improve HER performance of grown electro-catalyst but also facilitate OER kinetics which is considered sluggish for most bi-functional electrocatalysts. This review presents the significance of MXenes as HER, OER, and bi-functional electrocatalysts by discussing the electrocatalytic properties of a wide range of MXenes and how their hetero-structures affect HER, OER, and bi-functional electrocatalytic performance. In the end, the current challenges, and future perspectives of MXenes and their nanocomposites for water electrolysis have been discussed. • Review of recent trends in electrochemical water splitting (HER, OER, Overall) using MXene and their heterostructures. • Role of different functional groups, morphology and MXene composition on electrochemical water splitting. • Design strategies for constructing MXene/nanostructures. • Strategies for optimizing electrocatalytic properties of MXene/nanostructures. [ABSTRACT FROM AUTHOR]

• Hydrothermal reaction engaged to formulate the WS 2 decorated MXene/GO composites. • A composite electrode offered the high capacitance of 1111F.g−1 with high cycling stability. • WS 2 @MXene/GO exposed the asymmetric capacitance of 420F g−1 and specific energy of 114 Wh.kg −1. • WS 2 @MXene/GO offered the noble metal like HER behavior under the acid and alkaline condition. MXene-related materials are auspicious electrodes for energy storage/conversion application due to their various features, including large surface area, high metallic conductivity, and fast redox activity; however, their surface aggregation and oxidation have significantly restricted their application in various industries. This study demonstrated the fabrication of porous WS 2 nanosheets-interconnected MXene/GO (WS 2 @MXene/GO) nanocomposites using a simple hydrothermal reaction for electrochemical supercapacitors and water splitting reactions. The assembled WS 2 @MXene/GO nanocomposites electrode produced a superior specific capacitance of ∼ 1111F g−1 at 2 A/g applied current. Further, the asymmetric device constructed using the nanocomposite delivered the high specific energy of ∼ 114 Wh kg−1 and asymmetric capacitance of 320F g−1 along with an exceptional cycling stability. The WS 2 @MXene/GO nanocomposites electrocatalyst exhibited low overpotentials of 42 and 45 mV and small Tafel slopes values of 43 and 58 mV.dec−1 for hydrogen evolution reaction in acidic and alkaline medium, respectively. In addition, density functional theory (DFT) approximations validated the observed experimental results using density of states, Gibbs free energy for H-adsorption, and quantum capacitance calculations. [ABSTRACT FROM AUTHOR]