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Anthropogenic CO2 emissions from fossil fuel combustion have led to the serious environmental consequence of global warming and associated climate change. Valorization of CO2 to value-added chemicals by electrochemical reduction has been suggested as one of the promising approaches of CO2 attenuation owing to its simple operational requirements and ambient process conditions. However, the sluggish kinetics and high overpotential of several CO2 reduction processes remain a challenge to its practical utility unless efficient electrocatalysts are applied. Over the past years, several electrocatalysts have been reported for the purpose with varying degree of success. In the current review, we critically evaluate the efficiency of various reported catalysts systems summarizing their advantages as limitations and providing insights into their mechanism of action. Based on the detailed review of different catalysts systems the outlook and future directions are proposed. [ABSTRACT FROM AUTHOR]

Novel BiOBr/Cd(OH)2 heterostructures were synthesized by a facile chemical bath method under ambient conditions. A series of BiOBr/Cd(OH)2 heterostructures were obtained by tuning the Bi/Cd molar ratios. The obtained heterostructures were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Optical properties were studied by UV-visible spectroscopy, diffuse reflectance spectroscopy and photoluminescence (PL). Photocatalytic studies on rhodamine B (RhB) under visible light irradiation showed that the heterostructures are very efficient photocatalysts in mild basic medium. Scavenger test studies confirmed that the photogenerated holes and superoxide radicals (O2Ṗ−) are the main active species responsible for RhB degradation. Comparison of photoluminescence (PL) intensity suggested that an inhibited charge recombination is crucial for the degradation process over these photocatalysts. Moreover, relative positioning of the valence and conduction band edges of the semiconductors, O2/O2Ṗ− and ṖOH/H2O redox potentials and HOMO–LUMO levels of RhB appear to be responsible for the hole-specificity of degradation. Photocatalytic recycling experiments indicated the high stability of the catalysts in the reaction medium without any significant loss of activity. This study hence concludes that the heterojunction constructed between Cd(OH)2 and BiOBr interfaces play a crucial role in influencing the charge carrier dynamics and subsequent photocatalytic activity. [ABSTRACT FROM AUTHOR]

In line with current research goals involving water splitting for hydrogen production, this work aims to develop a noble-metal-free electrocatalyst for a superior hydrogen evolution reaction (HER). A single-step interfacial activation of Ti 3 C 2 T x MXene layers was employed by uniformly growing embedded WS 2 two-dimensional (2D) nanopetal-like sheets through a facile solvothermal method. We exploited the interactions between WS 2 nanopetals and Ti 3 C 2 T x nanolayers to enhance HER performance. A much safer method was adopted to synthesize the base material, Ti 3 C 2 T x MXene, by etching its MAX phase through mild in situ HF formation. Consequently, WS 2 nanopetals were grown between the MXene layers and on edges in a one-step solvothermal method, resulting in a 2D-2D nanocomposite with enhanced interactions between WS 2 and Ti 3 C 2 T x MXene. The resulting 2D-2D nanocomposite was thoroughly characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses before being utilized as working electrodes for HER application. Among various loadings of WS 2 into MXene, the 5% WS 2 -Ti 3 C 2 T x MXene sample exhibited the best activity toward HER, with a low overpotential value of 66.0 mV at a current density of -10 mA cm -2 in a 1 M KOH electrolyte and a remarkable Tafel slope of 46.7 mV·dec -1 . The intercalation of 2D WS 2 nanopetals enhances active sites for hydrogen adsorption, promotes charge transfer, and helps attain an electrochemical stability of 50 h, boosting HER reduction potential. Furthermore, theoretical calculations confirmed that 2D-2D interactions between 1T/2H-WS 2 and Ti 3 C 2 T x MXene realign the active centers for HER, thereby reducing the overpotential barrier.

Photocatalytic CO 2 reduction into C1 products is one of the most trending research subjects of current times as sustainable energy generation is the utmost need of the hour. In this review, we have tried to comprehensively summarize the potential of supramolecule-based photocatalysts for CO 2 reduction into C1 compounds. At the outset, we have thrown light on the inert nature of gaseous CO 2 and the various challenges researchers are facing in its reduction. The evolution of photocatalysts used for CO 2 reduction, from heterogeneous catalysis to supramolecule-based molecular catalysis, and subsequent semiconductor-supramolecule hybrid catalysis has been thoroughly discussed. Since CO 2 is thermodynamically a very stable molecule, a huge reduction potential is required to undergo its one- or multielectron reduction. For this reason, various supramolecule photocatalysts were designed involving a photosensitizer unit and a catalyst unit connected by a linker. Later on, solid semiconductor support was also introduced in this supramolecule system to achieve enhanced durability, structural compactness, enhanced charge mobility, and extra overpotential for CO 2 reduction. Reticular chemistry is seen to play a pivotal role as it allows bringing all of the positive features together from various components of this hybrid semiconductor-supramolecule photocatalyst system. Thus, here in this review, we have discussed the selection and role of various components, viz. the photosensitizer component, the catalyst component, the linker, the semiconductor support, the anchoring ligands, and the peripheral ligands for the design of highly performing CO 2 reduction photocatalysts. The selection and role of various sacrificial electron donors have also been highlighted. This review is aimed to help researchers reach an understanding that may translate into the development of excellent CO 2 reduction photocatalysts that are operational under visible light and possess superior activity, efficiency, and selectivity., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)