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Bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are the heart of metal-air batteries, fuel cells, and other energy storage systems. Here, we report a series of a novel class of redox-active viologen-based ionic covalent organic networks (vCONs) which are directly used as metal-free bifunctional electrocatalysts towards ORR and OER applications. These vCONs (named vGC, vGAC, vMEL and vBPDP) were synthesized by the well-known Zincke reaction. The installation of redox-active viologen moieties among the extended covalent organic architectures played a crucial role for exceptional acid/base stability, as well as bifunctional ORR and OER activities, confirmed by the cyclic voltammetry (CV) curves. Among all of them, vBPDP showed high ORR efficiency with a half-wave potential of 0.72 V against a reversible hydrogen electrode (RHE) in 1 M KOH electrolyte. In contrast, vMEL demonstrated high OER activity with an overpotential of 320 mV at a current density of 10 mAcm-2 and a Tafel slope of 109.4 mV dec-1 in 1 M KOH electrolyte solution. This work is exceptional and unique in terms of directly used pristine ionic covalent organic networks that are used as bifunctional (ORR and OER) electrocatalysts without adding any metals or conductive materials.

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CdS-based materials are extensively studied for photocatalytic water splitting. By incorporating Ag+ into CdS nanomaterials, the catalyst's charge carrier dynamic can be tuned for photo-electrochemical devices. However, photo-corrosion and air-stability of the heterostructures limit the photocatalytic device's performance. Here, a one-pot, single molecular source synthesis of the air-stable AgCdS ternary semiconductor alloy nanostructures by heat-up method is reported. Monoclinic and hexagonal phases of the alloy are tuned by judicious choice of dodecane thiol (DDT), octadecyl amine (ODA), and oleyl amine (OLA) as capping agents. Transmission electron microscope (TEM) and powder X-ray diffraction characterization of the AgCdS alloy confirm the monoclinic and hexagonal phase (wurtzite) formation. The high-resolution TEM studies confirm the formation of AgCdS@DDT alloy nanorods and their shape transformation into nano-triangles. The nanoparticle coalescence is observed for ODA-capped alloys in the wurtzite phase. Moreover, OLA directs mixed crystal phases and anisotropic growth of alloy. Optical processes in AgCdS@DDT nano-triangles show mono-exponential decay (3.97 ± 0.01 ns). The monoclinic phase of the AgCdS@DDT nanorods exhibits higher electrochemical hydrogen evolution activity in neutral media as compared to the AgCdS@ODA/OLA alloy nanocrystals. DDT and OLA-capped alloys display current densities of 14.1 and 14.7 mA cm-2 , respectively, at 0.8 V (vs RHE).

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Development of highly efficient and robust electrocatalysts for oxygen evolution reaction (OER) under specific electrolyte is a key to actualize commercial low-temperature water electrolyzers. Herein, a rational catalyst design strategy is first reported based on amorphous-crystalline (a-c) interfacial engineering to achieve high catalytic activity and durability under diverse electrolytes that can be used for all types of low-temperature water electrolysis. Abundant a-c interface (ACI) is implemented into a hollow nanocubic (pre)-electrocatalyst which is derived from Ir-doped Ni-Fe-Zn Prussian blue analogues (PBA). The implemented c-a interface is well maintained during prolonged OER in alkaline, alkalized saline, and acidic electrolytes demonstrating its diverse functionality for water electrolysis. Notably, the final catalyst exhibits superior catalytic activity with excellent durability for OER compared to that of benchmark IrO2 catalyst, regardless of chemical environment of electrolytes. Hence, this work can be an instructive guidance for developing the ACI engineered electroctalyst which can be diversely used for different types of low-temperature electrolyzers.

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In this paper, we report the fundamental electrical transport properties measured in Bi2Se3-AgMnOOH nanocomposite disc, which is prepared for the first time by convenient low temperature solution-phase chemistry in conjunction with redox-mediated methodology. The comparative structural and morphological analyses for the nanocomposite with pristine Bi2Se3 are comprehensively investigated by different material characterization techniques. The results demonstrate the successful in situ composite fabrication between the Bi2Se3, Ag and γ-MnOOH components. Besides, the present work introduces a systematic approach for the examination of electrical transport properties in Ohmic and non-Ohmic regimes over a wide temperature range. The results from the room temperature transport measurement exhibited that the nanocomposite demonstrated non-linearity after a certain current I0 (onset current), whereas Bi2Se3 was linear in the entire measured current range. An enhancement of the conductance was observed for Bi2Se3-AgMnOOH compared to the pure Bi2Se3 material, which is credited to the composite effect. The onset exponents xT (DC conductance) and xf (AC conductance) with phase-sensitive character demonstrate different values below and above 180 K separating two different phases with different conduction mechanisms. Also, flicker noise analysis established the correlation between the DC conductance in terms of Ohmic to non-Ohmic transition after the onset voltage V0. This transition phenomenon from Ohmic to non-Ohmic behaviour is explained from the structural point of view of the nanocomposite. The present investigation highlights the importance of using the bottom-up solution-phase strategy for the synthesis of high quality Bi2Se3-based nanocomposites for transport studies and their possible future applications.

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Oxygen evolution reaction (OER) under acidic conditions becomes of significant importance for the practical use of a proton exchange membrane (PEM) water electrolyzer. In particular, maximizing the mass activity of iridium (Ir) is one of the maiden issues. Herein, the authors discover that the Ir-doped calcium copper titanate (CaCu3Ti4O12, CCTO) perovskite exhibits ultrahigh mass activity up to 1000 A gIr -1 for the acidic OER, which is 66 times higher than that of the benchmark catalyst, IrO2 . By substituting Ti with Ir in CCTO, metal-oxygen (M-O) covalency can be significantly increased leading to the reduced energy barrier for charge transfer. Further, highly polarizable CCTO perovskite referred to as "colossal dielectric", possesses low defect formation energy for oxygen vacancy inducing a high number of oxygen vacancies in Ir-doped CCTO (Ir-CCTO). Electron transfer occurs from the oxygen vacancies and Ti to the substituted Ir consequentially resulting in the electron-rich Ir and -deficient Ti sites. Thus, favorable adsorptions of oxygen intermediates can take place at Ti sites while the Ir ensures efficient charge supplies during OER, taking a top position of the volcano plot. Simultaneously, the introduced Ir dopants form nanoclusters at the surface of Ir-CCTO, which can boost catalytic activity for the acidic OER.

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Graphitic carbon nitride (GCN), a polymeric metal free catalyst is widely used to degrade the toxic organic dye from the aqueous pollution. However, its catalytic efficiency and effective simultaneous reduction of mixed dye is still a challenge. Here, we have tuned the physiochemical properties of the GCN and melem derivatives by facilely tuning the degree of polycondensation and examined their catalytic activity towards the removal of cationic dye individually and together in solution. Catalysts were synthesized by thermal treatment of low-cost melamine and characterized by XRD, FTIR, RAMAN, FE-SEM, EDX, UV-DRS, and FL spectroscopy to confirm materials' structure, phase, morphology and optical properties. A suitable phase of the catalyst (M-450) exhibited superior removal capacity with a high-rate constant compared to others. The results demonstrate that M-450 has a maximum loading efficacy of 2.13 and 1.12 mg g-1 for methylene blue (MB) and Rhodamine B (RhB) dyes respectively in a single dye system. Attractively, when MB and RhB co-exist in the solution, the efficacy increased by 14% (2.44 mg g-1) and 27% (1.43 mg g-1) for MB and RhB respectively. The adsorption kinetics, stability, effect of pH and reusability of M-450 catalyst was testified. Further, radical scavenger experiments and terephthalic acid tests were carried out to explain the reaction mechanism involved in the degradation of textile dyes. Moreover, electron paramagnetic resonance (EPR) analysis validated the availability of hydroxyl radicals in the photocatalytic reaction. Excellent stability and reusability were attained even after five successive cycles, demonstrating a suitable photocatalyst for the efficient degradation of mixed dye.

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Herein, for the first time, we applied the metal-metal-bond-energy factor to the evolution of a porous Se-Te alloy. The porous Se-Te material has been prepared from the constituents' elemental states, through only a heating-cooling process in silicone oil without the use of any reagent, surfactant, or capping agent. Surprisingly, the reaction occurred at a much lower temperature (240 °C) than the mp (450 °C) of Te0. The reaction's nucleation and growth by means of varied bond energy have been clarified for the first time. A difference in the bond energies of a hetero metal-metal bond (Se-Te) and a homo metal-metal bond (Se-Se) directs nucleation and growth toward the fabrication of a porous structure, even from the constituents' elemental states, in which low-angle-grain-boundary (LAGB) and high-angle-grain-boundary (HAGB) movements play governing roles. Proper band-gap alignment of Se and Te makes the alloy composite applicable to water-splitting reactions under Xe-arc-lamp illumination. PEC efficiency of Se-Te was found to be higher than those reported for Se and other composite materials.

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We report enhanced catalytic activity of CuO nanopetals synthesized by microwave-assisted wet chemical synthesis. The catalytic reaction of CuO nanopetals and H2O2 was studied with the application of external light source and also under dark conditions for the degradation of the hazardous dye methylene blue. The CuO nanopetals showed significant catalytic activity for the fast degradation of methylene blue and rhodamine B (RhB) under dark conditions, without the application of an external light source. This increased catalytic activity was attributed to the co-operative role of H2O2 and the large specific surface area (≈40 m2·g-1) of the nanopetals. We propose a detail mechanism for this fast degradation. A separate study of the effect of different H2O2 concentrations for the degradation of methylene blue under dark conditions is also illustrated.

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An efficient, cost-effective, and earth-abundant catalyst that could drive the production of hydrogen from water without or with little external energy is the ultimate goal toward hydrogen economy. Herein, nanoplates of tungsten oxide and its hydrates (WO3·H2O) as promising electrocatalysts for the hydrogen evolution reaction (HER) are reported. The square-shaped and stacked WO3·H2O nanoplates are synthesized at room temperature under air in ethanol only, making it as a promising green synthesis strategy. The repeated electrochemical cyclic voltammetry cycles modified the surface of WO3·H2O nanoplates to WO3 as confirmed by X-ray photoelectron and Auger spectroscopy, which leads to an improved HER activity. Hydrogen evolution is further achieved from distilled water (pH 5.67) producing 1 mA cm-2 at an overpotential of 15 mV versus the reversible hydrogen electrode. Moreover, WO3·H2O and WO3 nanoplates demonstrate excellent durability in acidic and neutral media, which is highly desirable for practical application. Improved hydrogen evolution by WO3(200) when compared to that by Pt(111) is further substantiated by the density functional theory calculations.

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The synthesis of nanostructured materials without any hazardous organic chemicals and expensive capping reagents is one of the challenges in nanotechnology. Here we report on the L-arginine (a biomolecule)-assisted synthesis of single crystalline cubic In(OH)3 nanocubes of a size in the range of 30-60 nm along the diagonal using hydrothermal methods. Upon calcining at 750 °C for 1 h in air, In(OH)3 nanocubes are transformed into In2O3 nanoparticles (NPs) with voids. The morphology transformation and formation of voids with the increase of the calcination temperature is studied in detail. The possible mechanism of the voids' formation is discussed on the basis of the Kirkendall effect. The photocatalytic properties of In(OH)3 nanocubes and In2O3 NPs are studied for the degradation of rhodamin B and alizarin red S. Furthermore, the CO oxidation activity of In(OH)3 nanocubes and In2O3 NPs is examined. The photocatalytic and CO oxidation activity are measured to be higher for In2O3 NPs than for In(OH)3 nanocubes. This is attributed to the lower energy gap and higher specific surface area of the former. The present green synthesis has potential for the synthesis of other inorganic nanomaterials.

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It remains a challenge to find a suitable gas sensing material that shows a high response and shows selectivity towards various gases simultaneously. Here, we report a mixed metal oxide WO3-SnO2 nanostructured material synthesized in situ by a simple, single-step, one-pot hydrothermal method at 200 °C in 12 h, and demonstrate its superior sensing behavior towards volatile organic compounds (VOCs) such as ammonia, ethanol and acetone. SnO2 nanoparticles with controlled size and density were uniformly grown on WO3 nanoplates by varying the tin precursor. The density of the SnO2 nanoparticles on the WO3 nanoplates plays a crucial role in the VOC selectivity. The responses of the present mixed metal oxides are found to be much higher than the previously reported results based on single/mixed oxides and noble metal-doped oxides. In addition, the VOC selectivity is found to be highly temperature-dependent, with optimum performance obtained at 200 °C, 300 °C and 350 °C for ammonia, ethanol and acetone, respectively. The present results on the cost-effective noble metal-free WO3-SnO2 sensor could find potential application in human breath analysis by non-invasive detection.