Bimetallic Organic Frameworks via In Situ Solvothermal Sol-Gel-Crystal and Sol-Crystal Transformation as Durable Electrocatalysts for Oxygen Reduction Reaction.

The in situ solvothermal conversion of metal-organic gels (MOGs) to crystalline metal-organic frameworks (MOFs) represents a versatile and ingenious strategy that has been employed for the synthesis of MOF materials with specific morphologies, high yield, and improved functional properties. Herein, we have adopted an in situ solvothermal conversion of bimetallic MOGs to crystalline bimetallic MOFs with the aim of introducing a redox-active metal heterogeneity into the monometallic counterpart. The formation of bimetallic NiZn-MOF and CoZn-MOF via in situ solvothermal sol-gel-crystal and sol-crystal transformation is found to depend on the solvent systems used. The sol-to-gel-to-crystal transformation of NiZn-MOF via the formation of NiZn-MOG is found to occur through the gradual disruption of gel fibers leading to subsequent formation of microcrystals and single crystals of NiZn-MOF. These bimetallic MOFs and MOGs serve as promising electrocatalysts for oxygen reduction reaction (ORR) with an excellent methanol tolerance property, which can be attributed to the enhanced mass and charge transfer, higher oxygen vacancies, and bimetallic synergistic interactions among the heterometals. This work demonstrates a convenient strategy for producing bimetallic MOGs to MOFs through the introduction of a redox-active metal heterogeneity in the inorganic hybrid functional materials for fundamental and applied research. Our results connect MOGs and MOFs which have been regarded as having opposite physical states, that is, soft vs hard, and provide promising structural correlation between MOGs and MOFs at the molecular level.

Effect of Cooperative Redox Property and Oxygen Vacancies on Bifunctional OER and HER Activities of Solvothermally Synthesized CeO2/CuO Composites.

Herein, we report the synthesis of the CeO2/CuO composite as a bifunctional oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) electrocatalyst in a basic medium. The electrocatalyst with an optimum 1:1 CeO2/CuO shows low OER and HER overpotentials of 410 and 245 mV, respectively. The Tafel slopes of 60.2 and 108.4 mV/dec are measured for OER and HER, respectively. More importantly, the 1:1 CeO2/CuO composite electrocatalyst requires only a 1.61 V cell voltage to split water to achieve 10 mA/cm2 in a two-electrode cell. The role of oxygen vacancies and the cooperative redox activity at the interface of the CeO2 and CuO phases is explained in the light of Raman and XPS studies, which play the determining factor for the enhanced bifunctional activity of the 1:1 CeO2/CuO composite. This work provides guidance for the optimization and design of a low-cost alternative electrocatalyst to replace the expensive noble-metal-based electrocatalyst for overall water splitting.

A core-shell magnet Mn70Bi30grown at seeds in magnetic fields and its impacts on its spin-dynamics, Curie point and other tailored properties.

The MnBi alloys is a model series of rare-Earth free magnets for surge of technologies of small parts of automobiles, power generators, medical tools, memory systems, and many others. The magnetics stem primarily at unpaired Mn-3d5spins (a 4.23µBmoment) align parallel via an orbital moment 0.27µBof Bi-5d106s2p3in a crystal lattice. Thus, using a surplus Mn (over Bi) in a Mn70Bi30type alloy designs a spin-rich system of duly tailored properties useful for magnetics and other devices. In this view, we report here a strategy of a refined alloy powder Mn70Bi30can grow into small crystals of hexagonal (h) plates at seeds as annealed in magnetic fields (in H2gas). So, small h-plates (30 to 50 nm widths) are grown up at (002) facets, wherein the edges are turned down in a spiral (≤2.1 nm thicknesses) in a core-shell structure. The results are described with x-ray diffraction, lattice images and magnetic properties of a powder Mn70Bi30(milled in glycine) is annealed at 573 K for different time periods, so to the Mn/Bi order at the permeable facets (seeds). Duly annealed samples exhibit an enhanced magnetization,Ms→ 70.8 emu g-1, with duly promoted coercivityHc→ 10.810 kOe (15.910 kOe at 350 K), energy-product 14.8 MGOe, and the crystal-field-anisotropy,K1→ 7.6 × 107erg cm-3, reported at room temperature. Otherwise,Msshould decline at any surplus 3d5-Mn spins order antiparallel at the antisites. Enhanced Curie point 658.1 K (628 K at Mn50Bi50alloy) anticipates that a surplus Mn does favor the Mn-Bi exchange interactions. Proposed spin models well describe the spin-dynamics and lattice relaxations (on anneals) over the lattice volume (with twins) and spin clusters.

Room Temperature Acid-Free Greener Synthesis of Imine Using Cobalt-Doped Manganese Tungstate.

Facile synthesis of an imine compound through a greener route is still a challenging task. Industrial processes rely on the age-old Schiff reaction for the synthesis of imine, which are reversible and nongreen from an environmental viewpoint. Herein, cobalt-doped manganese tungstate with two different morphologies is synthesized and demonstrated as a recyclable catalyst for imine synthesis from the condensation of an aldehyde and an amine with 73% yield of an imine in a nonaqueous and nonacidic environment at room temperature. The high catalytic activity is attributed to cobalt doping, high surface area, strong acidic site, and the polar nature of the catalyst. The stability and recyclability test shows that the catalytic activity remains the same after several cycles, which is crucial from the industrial point of view. The formation of imine is found to follow an alternative mechanism in an irreversible manner with a polar four-membered intermediate unlike the conventional method. The demonstrated process has several advantages including irreversibility, "greener", environmental friendly, and energy-efficient.

Structurally modified V2O5based extrinsic pseudocapacitor.

Rapidly changing demand on energy storage systems makes it essential to redesign the device architecture and materials required to fabricate the devices. It is crucial to introduce capacitive behaviour in a conventional energy storage device (batteries) to improve the lifetime and power efficiency of the hole energy storage system. The charge storing nature of electrode material primarily depends on particle size, grain size, the electrode's chemical structure, and effective diffusion lengths for electrolytes within the electrode. Here V2O5based Li-ion battery electrode is transformed into a Li-ion pseudocapacitive electrode by structural modifications. The modified structures are achieved by optimizing reaction pressure to obtain larger, medium and smaller V2O5particles (namely, V2O5-L, V2O5-M and V2O5-S). As a result, the plateau regions in galvanostatic charge-discharge plots and highly intense redox peaks in the CV plots of V2O5-L get flattened for V2O5-S. Also, the lucrative improvement in rate capabilities and stability for V2O5-S indicates induced pseudocapacitance in V2O5. Some devices are fabricated with the extrinsic pseudocapacitive material (V2O5-S), providing 4.36 mWh cm-3volumetric energy density with 125 mW cm-3volumetric power density. The device retains around 95% of its initial capacitance after 10k cycles and holds up to 63% after 25k stability cycles.

Structural ordering at magnetic seeds with twins at boundaries of a core-shell alloy Mn60Bi40and tailored magnetic properties.

A spin Mn3d5-rich Mn60Bi40alloy reveals a model system in order to tailor profound magnetic properties at unpaired 3d5spins in such alloys of a core-shell structure. As annealed (at a critical temperature 573 K in H2gas), a refined powder (in glycine) grows onα-MnBi seeds (crystallites) present in it at Mn/Bi atoms order over topological layers, preferentially along (110) planes, at a self-confined structure at seeds of an anisotropic shape of hexagonal (h) plates (25-85 nm widths). In terms of the HRTEM images, the atoms turn down at edges (at the plates grow up) in a spiral layer, ≤ 2.1 nm thickness, of small core-shells. A spin model is proposed to delineate a way at the spins can pin down at the edges, form single magnetic domains, and raise coercivity (Hc), with no much loss of net magnetic moment. The X-ray diffraction and HRTEM images corroborate the results of topological pacing of atoms at the h-plates at anneals. A novelty is that a core-shell leads to tailor a superbHc, as much as 11.110 kOe (16.370 kOe at 350 K), with a fairly large magnetization, 76.5 emu g-1, at near 300 K. An enhanced Curie point 650.1 K (628 K at Mn50Bi50alloy) confers a surplus 3d5-Mn spin sensitively tunesα-MnBi stoichiometry and so its final magnetic structure. A refined alloy powder so made is useful to make powerful magnets and devices in the forms of films and bonded magnets in different shapes for uses as small tools, tweezers, and other devices.

Small core-shell Mn0.5Bi0.5-Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties.

The binary alloy Mn0.5+xBi0.5-x, x ⩽ 0.05, is a promising rare-earth-free magnetic material, with high-energy-density (a critical characteristic for electric motors and power electronics), low cost, and significant magnetic properties for multiple uses at room temperature. In this article, we report how a free Bi, when precipitated over Mn0.5+xBi0.5-x (x ⩽ 0.05) of small crystallites, diffuses back into a stable Mn0.5+xBi0.5-x, x → 0, via a peritectic reaction, which facilitates preferential growth of small core-shell crystallites with multiple facets, having the potential for tailored magnetic properties. This growth travels slowly in the anisotropic channels of vacancies on annealing the reactive nanopowder at a critical 573 K temperature in Ar gas. Thus, an initial crystallite size of D ∼ 27 nm grows to only 38 nm in a reaction extended over a period of 96 h. A transient phase, x > 0, which has Bi vacancies, primarily grows in the (101) and (110) facets, filling the vacancies over a 6.41% larger crystal density. If any excess Mn is present, it segregates over a saturated phase, combines with free Bi, and ultimately forms a stable alloy phase. The small crystallites contain an inbuilt surface Bi-layer (shell), with a 1-2 nm thickness, in a core-shell of nanoplates (20-60 nm width), as shown in the high resolution transmission electron microscope images. In the proposed microscopic model, with hybridized Mn-d5 and Bi-p3 electrons (also spins), the magnetic properties are readily controlled. Thus, at 300 K, a maximum coercivity Hc = 9.850 kOe (14.435 kOe at 350 K) develops (Hc = 5.010 kOe in the initial) in critical single domains (D ∼ 33 nm). A net 72.5 emu g-1 magnetization occurs, with an enhanced TC = 641.5 K (600.5 K at x ∼ 0.05) on an order of enhanced anisotropy constant K1, demonstrating the significant effects of this core-shell structure of small crystallites.

Isostructural NiII Metal-Organic Frameworks (MOFs) for Efficient Electrocatalysis of Oxygen Evolution Reaction and for Gas Sorption Properties.

Design and synthesis of stable, active and cost-effective electrocatalyst for water splitting applications is an emerging area of research, given the depletion of fossil fuels. Herein, two isostructural NiII redox-active metal-organic frameworks (MOFs) containing flexible tripodal trispyridyl ligand (L) and linear dicarboxylates such as terephthalate (TA) and 2-aminoterphthalate (H2 NTA) are studied for their catalytic activity in oxygen evaluation reaction (OER). The 2D-layered MOFs form 3D hydrogen bonded frameworks containing one-dimensional hydrophilic channels that are filled with water molecules. The electrochemical studies reveal that MOFs display an efficient catalytic activity towards oxygen evolution reaction in alkaline conditions with an overpotential as low as 356 mV. Further, these 2D-MOFs exhibit excellent ability to adsorb water vapor (180-230 cc g-1 at 273 K) and CO2 (33 cc g-1 at 273 K). The presence of hydrophilic functionality in the frameworks was found to significantly enhance the electrocatalytic activity as well as H2 O sorption.

Quantum capacitance tuned flexible supercapacitor by UV-ozone treated defect engineered reduced graphene oxide forest.

A forest like 3D carbon structure formed by reduced graphene oxide (RGO) was prepared to use as an electrode material for a highly power efficient supercapacitor. To improve the specific energy of the electrode, pore like defects were incorporated on the RGO forests by atomic oxygen etching, during the UV-ozone treatment. The modified surface helps to increase the net capacitance by permitting the electrolyte to the inner core of the active material and improving the minimal quantum capacitance. Density functional theory based first principle studies were carried out to find DOS at the Fermi level of defect induced RGO sheet and hence to validate the effect of quantum capacitance on net capacitance. Specific capacitance of RGO forest was increased by almost 150% after introduction of the defects. The best performing material exhibits 18.87 mF cm-2 areal capacitance at 2 mA cm-2 current density which is equivalent to 70 F cm-3 at 3.7 A cm-3 current density, and it was used to fabricate the supercapacitor. Two supercapacitors were fabricated, (i) on graphite sheet (non-flexible) and (ii) on scotch tape (flexible). Here PVA-KOH gel soaked filter paper was used as electrolyte-separator. Both the prepared supercapacitors on graphite sheet and scotch tape are able to transfer electrical energy with ultra high specific power (656.25 mW cm-3 and 164.06 mW cm-3 respectively) while maintaining moderate energy densities. The first device can withstand its primary capacitance by 90% even after 10 K charge-discharge cycles and the flexible device was able to hold 96% of its capacitance after 1 K bending cycles.

Exposed Facets-Dependent Catalytic Properties of Nanocrystals: Noble Metals (Pd, Pt, and Au) and Oxides of First Row d-Block Elements.

This review focuses on the recent progress in shape-controlled synthesis and exposed facets-dependent catalytic properties of widely used nanostructured noble metals (Pd, Pt, and Au), bimetallic alloys involving one noble metal, and oxides of first row d-block elements such as titanium oxide (TiO2), vanadium oxide (V2O5), chromium oxide (Cr2O3), manganese oxide (MnO2), iron oxide (Fe2O3), cobalt oxide (Co3O4), nickel oxide (NiO), copper oxide (Cu2O), and zinc oxide (ZnO). The major emphasis is given on the role of shape-controlling agents and experimental parameters to control the exposed facets of the nanocrystals. The importance of different high-index and high-energy exposed facets of noble metals and metal oxides with larger number of unsaturated atoms, edges, vertices, in different catalytic applications is presented. Furthermore, the synergy of both low-energy and high-energy exposed facets for efficient electron-hole separation for enhanced photocatalytic activity is discussed.

Bimetallic Au@M (M = Ag, Pd, Fe, and Cu) Nanoarchitectures Mediated by 1,4-Phenylene Diisocyanide Functionalization.

Hybridization with gold has attracted a lot of attention in many application areas such as energy, nanomedicine, and catalysts. Here, we demonstrate electrochemical hybridization of two different metals by using bare and 1,4-phenylene diisocyanide (PDI) functionalized gold nanoislands (GNIs) supported on a Si substrate. As pristine GNIs are not tightly locked on the Si surface, bimetallic Au@M (M = Ag, Pd, Fe, and Cu) core-shell type nanostructures are produced by an electric-field-induced clustering of GNIs and metal deposition. On the other hand, upon functionalization of GNIs by PDI, 3D island growth on the functionalized GNI template is observed as PDI acts as a protector against the electric-field-induced clustering. Depth-profiling X-ray photoelectron spectroscopy reveals no discernible difference in the interfacial electronic structures of hybrid metals prepared by using pristine and PDI-functionalized GNI templates. This work demonstrates a new approach to produce a secured template and to manipulate growth of hybrid nanoparticles on this template supported on a Si substrate by using electrodeposition and organic functionalization.

Controlled Synthesis of CuS/TiO2 Heterostructured Nanocomposites for Enhanced Photocatalytic Hydrogen Generation through Water Splitting.

Photocatalytic hydrogen (H2) generation through water splitting has attracted substantial attention as a clean and renewable energy generation process that has enormous potential in converting solar-to-chemical energy using suitable photocatalysts. The major bottleneck in the development of semiconductor-based photocatalysts lies in poor light absorption and fast recombination of photogenerated electron-hole pairs. Herein we report the synthesis of CuS/TiO2 heterostructured nanocomposites with varied TiO2 contents via simple hydrothermal and solution-based process. The morphology, crystal structure, composition, and optical properties of the as-synthesized CuS/TiO2 hybrids are evaluated in detail. Controlling the CuS/TiO2 ratio to an optimum value leads to the highest photocatalytic H2 production rate of 1262 µmol h-1 g-1, which is 9.7 and 9.3 times higher than that of pristine TiO2 nanospindles and CuS nanoflakes under irradiation, respectively. The enhancement in the H2 evolution rate is attributed to increased light absorption and efficient charge separation with an optimum CuS coverage on TiO2. The photoluminescence and photoelectrochemical measurements further confirm the efficient separation of charge carriers in the CuS/TiO2 hybrid. The mechanism and synergistic role of CuS and TiO2 semiconductors for enhanced photoactivity is further delineated.

Machine-Learning-Based Cyclic Voltammetry Behavior Model for Supercapacitance of Co-Doped Ceria/rGO Nanocomposite.

This paper examines the cobalt-doped ceria/reduced graphene oxide (Co-CeO2/rGO) nanocomposite as a supercapacitor and modeling of its cyclic voltammetry behavior using Artificial Neural Network (ANN) and Random Forest Algorithm (RFA). Good agreement was found between experimental results and the predicted values generated by using ANN and RFA. Simulation results confirmed the accuracy of the models, compared to measurements from supercapacitor module power-cycling. A comparison of the best performance between ANN and RFA models shows that the ANN models performed better (value of coefficient of determination >0.95) than the RFA models for all datasets used in this study. The results of the ANN and RFA models could be useful in designing the unique nanocomposites for supercapacitors and other strategies related with energy and the environment.

The Design of a New Cobalt Sulfide Nanoparticle Implanted Porous Organic Polymer Nanohybrid as a Smart and Durable Water-Splitting Photoelectrocatalyst.

Development of an inexpensive, efficient and robust nanohybrid catalyst as a substitute for platinum in photoelectrocatalytic hydrogen production has been considered intriguing and challenging. In this study, the design and sequential synthesis of a novel cobalt sulfide nanoparticle grafted Porous Organic Polymer nanohybrid (CoSx @POP) is reported and used as an active and durable water-splitting photoelectrocatalyst in the hydrogen evolution reaction (HER). The specific textural and relevant chemical properties of as-synthesised nanohybrid materials (Co3 O4 @POP &CoSx @POP) were investigated by means of XRD, XPS, FTIR, 13 C CP MAS NMR, spectroscopy, HR-TEM, HAADF-STEM with the corresponding elemental mapping, FE-SEM and nitrogen physisorption studies. CoSx @POP has been evaluated as a superior photoelectrocatalyst in HER, achieving a current density of 6.43 mA cm-2 at 0 V versus the reversible hydrogen electrode (RHE) in a 0.5 m Na2 SO4 electrolyte which outperforms its Co3 O4 @POP analogue. It was found that the nanohybrid CoSx @POP catalyst exhibited a substantially enhanced catalytic performance of 1.07 µmol min-1 cm-2 , which is considered to be ca. 10 and 1.94 times higher than that of pristine POP and CoSx , respectively. Remarkable photoelectrocatalytic activity of CoSx @POP compared to Co3 O4 @POP toward H2 evolution could be attributed to intrinsic synergistic effect of CoSx and POP, leading to the formation of a unique CoSx @POP nanoarchitecture with high porosity, which permits easy diffusion of electrolyte and efficient electron transfer from POP to CoSx during hydrogen generation with a tunable bandgap, that straddles between the reduction and oxidation potential of water.

Biomolecule-assisted synthesis of In(OH)3 nanocubes and In2O3 nanoparticles: photocatalytic degradation of organic contaminants and CO oxidation.

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.

Reduction of start-up time through bioaugmentation process in microbial fuel cells using an isolate from dark fermentative spent media fed anode.

An electrochemically active bacteria Pseudomonas aeruginosa IIT BT SS1 was isolated from a dark fermentative spent media fed anode, and a bioaugmentation technique using the isolated strain was used to improve the start-up time of a microbial fuel cell (MFC). Higher volumetric current density and lower start-up time were observed with the augmented system MFC-PM (13.7 A/m(3)) when compared with mixed culture MFC-M (8.72 A/m(3)) during the initial phase. This enhanced performance in MFC-PM was possibly due to the improvement in electron transfer ability by the augmented strain. However, pure culture MFC-P showed maximum volumetric current density (17 A/m(3)) due to the inherent electrogenic properties of Pseudomonas sp. An electrochemical impedance spectroscopic (EIS) study, along with matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) analysis, supported the influence of isolated species in improving the MFC performance. The present study indicates that the bioaugmentation strategy using the isolated Pseudomonas sp. can be effectively utilized to decrease the start-up time of MFC.

Surface Tailoring-Modulated Bifunctional Oxygen Electrocatalysis with CoP for Rechargeable Zn-Air Battery and Water Splitting.

The transition metal phosphide (TMP)-based functional electrocatalysts are very promising for the development of electrochemical energy conversion and storage devices including rechargeable metal-air batteries and water electrolyzer. Tuning the electrocatalytic activity of TMPs is one of the vital steps to achieve the desired performance of these energy devices. Herein, we demonstrate the modulation of the bifunctional oxygen electrocatalytic activity of nitrogen-doped carbon-encapsulated CoP (CoP@NC) nanostructures by surface tailoring with ultralow amount (0.56 atomic %) of Ru nanoparticles (2.5 nm). The CoP at the core and the Ru nanoparticles on the shell have a facile charge transfer interaction with the encapsulating NC. The strong coupling of Ru with CoP@NC boosts the electrocatalytic performance toward oxygen reduction (ORR), oxygen evolution (OER), and hydrogen evolution (HER) reactions. The surface-tailored catalyst requires only 35 mV to deliver the benchmark current density of 10 mA·cm-2 for HER. A small potential gap of 620 mV between ORR and OER is achieved, making the catalyst highly suitable for the development of rechargeable zinc-air batteries (ZABs). The homemade ZAB delivers a specific capacity of 780 mA·hgZn-1 and peak power density of 175 mW·cm-2 with a very small voltaic efficiency loss (1.1%) after 300 cycles. The two-electrode water splitting cell (CoP@NC-Ru||CoP@NC-Ru) delivers remarkably low cell voltage of 1.47 V at the benchmark current density. Stable current density of 25 mA·cm-2 for 25 h without any significant change is achieved. Theoretical studies support the charge transfer interaction-induced enhanced electrocatalytic activity of the surface-tailored nanostructure.

Laterally Grown Strain-Engineered Semitransparent Perovskite Solar Cells with 16.01% Efficiency.

Hybrid organometallic halide perovskite-based semitransparent solar cell research has garnered significant attention recently due to their promising applications for smart windows, tandem devices, wearable electronics, displays, and sustainable internet-of-things. Though considerable progress has been made, stability, controlling the crystalline qualities, and growth orientation in perovskite thin films play crucial roles in improving the photovoltaic (PV) performance. Recently, strain modulation within the perovskite gathers an immense interest that is achieved by the ex situ process. However, little work is reported on in situ strain modulation, which is presented here. Apart from the challenges in the fabrication of high-efficiency perovskite solar cell (PSC) devices under ambient conditions, the stability of organic hole-transporting materials needs urgent attention. Herein, a single-step deposition of formamidiniumchloride (FACl)-mediated CH3NH3PbI3 (MAPbI3) thin films without an inert atmosphere and CuI as the inorganic hole-transporting material is demonstrated for their potential application toward semitransparent PSCs. The FACl amount in MAPbI3 (mg/mL) plays a critical role in controlling the crystallinity, growth orientations, and in situ strains, which modulate the charge carrier transport dynamics, thereby improving the efficiency of the PSC device. A photoconversion efficiency of 16.01% has been achieved from MAPbI3 with 20 mg/mL of FACl additive incorporation. The modification of the structural, electronic, and optical properties and the origin of strain in the as-synthesized MAPbI3 domains due to the addition of FACl are further validated with experimental findings in detail using density functional theory simulations.

Dimension-Controlled Synthesis of Hybrid-Mixed Halide Perovskites for Solar Cell Application.

Despite the rapid improvement of photovoltaic (PV) efficiency in hybrid organic-inorganic metal halide perovskites (HOIPs), the fabrication procedure of a compact thin film in a large-area application is still a tedious work. Apart from the quality of the thin film, the stability of the perovskite materials and the expensive organic hole transport layer (HTL) within the HOIP-based PV device are the major issues that need to be addressed prior to their commercialization. Herein, a unique glass rod-based facile fabrication technique for producing a compact and stable thin film utilizing a mixed-halide-based perovskite precursor solution is demonstrated. The fabricated devices deliver high photoconversion efficiency (PCE) without the use of any HTL and show an excellent stability under ambient conditions. By varying the organic CH3NH3I (MAI) and inorganic PbBr2 content, perovskite materials with different dimensions, i.e., 3D, 2D, and 1D, are synthesized to produce an active layer for PV devices. Although a 2D single-halide perovskite is reported earlier, herein two different mixed-halide 2D perovskites, i.e., MA2PbI2Br2 and MAPb2IBr4, are synthesized successfully, and their performance is compared in detail along with that of 1D and 3D mixed-halide perovskites. The facile synthesized mixed-halide 2D-based MA2PbI2Br2 perovskite shows a PCE of 10.14% with a high stability of 92% after 100 days without encapsulation, which is much superior as compared to that of the mixed-halide 3D MAPbIBr2. The semiconducting behavior as well as the nature of the bandgap of the synthesized compounds is examined by pursuing density functional theory calculations. Specifically, the role of iodine doping to modify the electronic band structure is investigated, and introduction of iodine is found to reduce the effective masses of both electrons and holes in the perovskite material.

Recent advances in non-noble metal-based oxide materials as heterogeneous catalysts for C-H activation.

As the world moves towards a more sustainable future, it is desirable to replace the homogeneous catalytic processes and conventional industrial processes with energy-efficient, cost-effective, and greener heterogeneous processes. In heterogeneous catalysis, non-noble metal-based oxide catalysts have been gaining traction recently, as they are affordable, highly stable, and thus appealing for different industrial uses. C-H activation is crucial to numerous organic reactions such as hydrogenation, oxidation, reduction, oxidative coupling, substitution, and C-C coupling. However, it is a challenging task due to its high bond energy and high kinetic barrier of C-H bond cleavage, making it inert in most conventional processes, thereby requiring efficient catalysts. In recent years, non-noble metal-based oxides have made a huge difference in the reactivity of the C-H bond through their tailored surface area, surface charge, redox properties, and oxygen vacancies. In this perspective article, we discuss the application of nanostructured non-noble metal oxides with tailored surface properties through nano-structuring, doping, vacancy creation, and heterostructure formation in reactions involving C-H activation as the key step. Specifically, we focus on the essential surface properties of catalysts that play a major role in the C-H activation reaction for sustainable industrial applications.