Heterobimetallic Synergism in Triple-Redox 2D Framework for Largely Boosted Water Oxidation and Flanked Carboxylic-Acid-Triggered Unconventional Tandem Catalysis.

A fish-bone-shaped and thermochemically stable 2D metal-organic framework (MOF) with multimodal active center-decked pore-wall is devised. Redox-active [Co2(COO)4] node and thiazolo[5,4-d]thiazole functionalization benefit this mixed-ligand MOF exhibiting electrochemical water oxidation with 375 mV overpotential at 10 mA cm-2 current density and 78 mV per dec Tafel slope in alkaline medium. Pair of oppositely oriented carboxylic acids aids postmetalation with transition metal ions to engineer heterobimetallic materials. Notably, overpotential of Ni2+ grafted triple-redox composite reduces to 270 mV with twofold declined Tafel slope than the parent MOF, ranking among the best-reported values, and outperforming majority of related catalysts. Significantly, turnover frequency and charge transfer resistance display 35.5 and 1.4-fold upsurge, respectively, with much uplifted chronopotentiometric stability and increase active surface area owing to synergistic Co(II)-Ni(II) coupling. The simultaneous presence of ─COOH and nitrogen-rich moieties renders this hydrogen-bonded MOF as acid-base synergistic catalyst for recyclable deacetalization-Knoevenagel reaction with >99% product yield under solvent-free mild condition. Besides control experiments, unique role of ─COOH as hydrogen-bond donor site in substrate activation is validated from comparing the performances of molecular-shearing approach-derived structurally similar unfunctionalized MOF, and the heterobimetallic composite. To the best of tandem Knoevenagel condensation, larger-sized acetal exhibits poor yield of α,ß-unsaturated dicyanides, and demonstrates pore-fitting-mediated size-selectivity.

Morphology-Dependent Electrocatalytic Behavior of Cobalt Chromite toward the Oxygen Evolution Reaction in Acidic and Alkaline Medium.

Exploiting an affordable, durable, and high-performance electrocatalyst for the oxygen evolution reaction (OER) under lower pH condition (acidic) is highly challengeable and much attractive toward the hydrogen-based energy technologies. A spinel CoCr2O4 is observed as a potential noble-metal-free candidate for OER in alkaline medium. The presence of Cr further leads to electronic structure modulation of Co3O4 and thereby greatly increases the corrosive resistance toward OER in acidic environment. Herein, a typical CoCr2O4 with three different morphologies was synthesized for the very first time and employed as an electrocatalyst for OER in alkaline (1 M KOH) and acidic (0.5 M H2SO4) medium. Moreover, different morphologies display a different intrinsic exposed active site and thereby display different electrocatalytic activities. Likewise, the CoCr2O4 Mic (synthesized by the microwave heating method) displays a higher catalytic activity toward OER and delivers a low overpotential of 293 and 290 mV to attain 10 mA/cm2 current density and smaller Tafel slope values of 40 and 151 mV/dec, respectively, in alkaline and acidic environment than the synthesized CoCr2O4 Wet (wet-chemically synthesized) and CoCr2O4 Hyd (hydrothermally synthesized). Moreover, CoCr2O4 Mic exhibits a long-term durability of 24 h (1 M KOH) and 10.5 h (0.5 M H2SO4). The optimized Co-O bond energy in OER condition makes the CoCr2O4 Mic superior than the CoCr2O4 Hyd and CoCr2O4 Wet. Moreover, the substitution of Cr induces the electron delocalization around the Co active species and thereby, positive shifting of the redox potential leads to providing an optimal binding energy for OER intermediates. Also, interestingly, this work represents a catalytic activity trend by a simple experimental result without any complex theoretical calculation. The morphology-dependent electrocatalytic activity obtained in this work will provide a new strategy in the field of electrochemical conversion and energy storage application.

Immobilization of Gold Nanoparticles on Postsynthetically Modified NU-1000 for Hydrogen Evolution Reaction.

NU-1000, being a hydrothermally stable metal-organic framework (MOF), with structural robustness is viable for functionalization with various entities. A postsynthetic modification strategy called solvent-assisted ligand incorporation (SALI) is chosen for functionalizing NU-1000 with thiol moieties using 2-mercaptobenzoic acid. In accordance with soft acid-soft base interactions, the thiol groups on NU-1000, as a scaffold, can immobilize the gold nanoparticles without much aggregation. The catalytically active gold sites on thiolated NU-1000 are utilized for hydrogen evolution reaction (HER). The catalyst delivered an overpotential of 101 mV at a current density of 10 mAcm-2 in 0.5 M H2SO4. The faster charge transfer kinetics determined from the Tafel slope of 44 mV/dec enhances the HER activity. The sustainable performance of the catalyst for 36 h proves its utility as a potential catalyst to produce neat hydrogen.

Exploring the Defect Sites in UiO-66 by Decorating Platinum Nanoparticles for an Efficient Hydrogen Evolution Reaction.

UiO-66 has been tailored using defect engineering methodology to introduce thiol functionalities into the MOF skeletal structure. The thiolated UiO-66 serves as a scaffold to support the platinum nanoparticles with a size of ∼2 nm through a soft-soft interaction. This Pt@UiO-66-SH, utilized as an HER catalyst, exhibited an overpotential of 57 mV at a current density of 10 mA cm-2 in an acidic medium with a Tafel slope of 75 mV/dec and a high TOF value (389.37 s-1). This catalyst showed long-term durability for 30 h, specifying the potential of the material to produce neat hydrogen.

Stabilization of Ru NPs over 3D LaCrO3 Nanostructures for High-Performance HER Catalysts in Acidic Media.

Hydrogen is considered as one of the best alternatives to carbon-based fossil fuels as energy sources. Electrocatalytic water splitting is one of the finest and eco-friendly methods for the production of hydrogen as compared to all other methods such as stream reforming carbon, hydrolysis of metal hydrides, etc. However, the sluggish kinetics on both the half-cell reactions limits the large-scale production of hydrogen. Hence, to overcome such kind of kinetic issues, designing a catalyst with characteristics of low overpotential and high stability is a matter of prime importance for the research community. Perovskite oxides are one of the well-documented materials for their excellent electrocatalytic water oxidation activity. But because of the lack of a proper proton adsorption site, these materials are unable to show proper hydrogen evolution reaction (HER) activity. Several strategies have been adopted for improving the HER activity of perovskite materials like cation doping, nanostructuring, etc. Here in this work, we prepared a shape-selective LaCrO3 (LCO) material. To enhance the electrocatalytic activity, we decorated the LCO with Ru nanoparticles via a hydrothermal method with different concentrations of Ru (Ru@LaCrO3), coined LCOn (n = 1-2.5). The as-synthesized RLCO2.5 showed the highest HER activity by demanding a low overpotential of 150 mV, whereas bare LCO demanded a higher overpotential of 364 mV to reach the benchmark current density of 10 mA/cm2. Also, RLCO2.5 showed a very low Rct value of 15.8 Ω and followed the facile kinetics with a lower Tafel value of 101 mV/dec. It also showed excellent stability over 55 h at a current density of 10 mA/cm2 in chronoamperometry studies. Acceleration degradation studies of RLCO2.5 showed comparably good activity with a small hike in overpotential toward HER. Hence, RLCO-based materials are highly helpful to develop efficient electrocatalysts to produce hydrogen in a large scale.

Tuning the Electronic Structure of a Ni-Vacancy-Enriched AuNi Spherical Nanoalloy via Electrochemical Etching for Water Oxidation Studies in Alkaline and Neutral Media.

Internal Ni-vacancy-enriched spherical AuNi nanoalloys (AuNi1-2-T) have been prepared via a noble electrochemical etching method. AuNi1.5-T showed the highest oxygen evolution reaction (OER) activity compared to bare AuNi1.5, and it demands only 239 mV overpotential, which was 134 mV lesser than the overpotential required by commercial RuO2 at 10 mA cm-2 current density in a 1 M KOH solution (pH = 14). The calculated turnover frequency (TOF) value for AuNi1.5-T (0.0229 s-1) was 11.74 times higher than that of AuNi1.5 (0.00195 s-1). Also, the electrochemically activated AuNi1.5-T showed superior neutral water oxidation activity by demanding only 335 mV overpotential with a TOF value of 0.000135 s-1 in a 1 M Na2SO4 solution (pH = 7) at 10 mA cm-2. The long-term stability studies (over 60 h) reveal the excellent robustness of an electrochemically treated alloy system. Density functional theory based electronic structure calculations showed that in the case of AuNi and AuNi1.5, Au d, Au s, and Ni d orbitals have significant contributions, whereas in the Ni-vacant systems, the density of states is mainly governed by d orbitals of Au and Ni. Also, the Ni-vacant system possesses a work function value of 4.96 eV, which is lower than that of the pristine system (5.27 eV) and thereby favored OH- binding with an optimum adsorption energy. This result is in reasonable agreement with the experimental outcome of an accelerated OER in a vacancy-enriched Ni-rich AuNi alloy system. Also, mechanistic analysis reveals that the creation of a Ni vacancy can effectively alter the overall mechanism of the OER and thereby facilitate the same with a lower applied energy.

Ruthenium-Doping-Induced Amorphization of VS4 Nanostructures with a Rich Sulfur Vacancy for Enhanced Hydrogen Evolution Reaction in a Neutral Electrolyte Medium.

The generation of pure H2 from a neutral electrolyte solution represents a transformative route with low cost and environmentally friendly nature. However, the complex kinetics of hydrogen evolution reaction (HER) via water electrolysis make its practical application to be difficult. Herein, we have reported Ru-doping-induced formation of VS4 nanostructures with a rich S vacancy for neutral HER in a 0.2 M phosphate buffer solution. The Ru-doped VS4 demands an overpotential value of 160 mV at 10 mA/cm2 current density with a lower catalyst loading of 0.1 mg/cm2, while pristine VS4 demands a 374 mV overpotential with the same mass loading. 60 hours of chronoamperometric study reveals the excellent stability of Ru-doped VS4 materials, which is the highest amount of time ever reported for neutral HER. The marginal degradation of a catalyst under a long-term stability study was confirmed through inductively coupled plasma mass spectrometry (ICP-MS) analysis. The introduction of Ru to the VS4 lattice leads to a 4.35-fold increase in the turnover-frequency values compared to those of bare VS4 nanostructures. The higher HER activity of S-vacancy-enriched VS4 materials is thought to originate through effective water adsorption in S vacancy and Ru3+ sites followed by the dissociation of a H2O molecule, and S22- efficiently converts Had to H2. Also, post-HER characterization reveals that the transformation of some Ru3+ to Ru0 additionally favored the HER by providing a better H adsorption site under a static cathodic potential.

Vanadium-Doped Nickel Cobalt Layered Double Hydroxide: A High-Performance Oxygen Evolution Reaction Electrocatalyst in Alkaline Medium.

Vast attention from researchers is being given to the development of suitable oxygen evolution reaction (OER) electrocatalysts via water electrolysis. Being highly abundant, the use of transition-metal-based OER catalysts has been attractive more recently. Among the various transition-metal-based electrocatalysts, the use of layered double hydroxides (LDHs) has gained special attention from researchers owing to their high stability under OER conditions. In this work, we have reported the synthesis of trimetallic NiCoV-LDH via a simple wet-chemical method. The synthesized NiCoV-LDH possesses aggregated sheet-like structures and is screened for OER studies in alkaline medium. In the study of OER activity, the as-prepared catalyst demanded 280 mV overpotential and this was 42 mV less than the overpotential essential for pristine NiCo-LDH. Moreover, doping of a third metal into the NiCo-LDH system might lead to an increase in TOF values by almost three times. Apart from this, the electronic structural evaluation confirms that the doping of V3+ into NiCo-LDH could synergistically favor the electron transfer among the metal ions, which in turn increases the activity of the prepared catalyst toward the OER.

Modulating the Surface Electronic Structure of Active Ni Sites by Engineering Hierarchical NiFe-LDH/CuS over Cu Foam as an Efficient Electrocatalyst for Water Splitting.

Water electrolysis encounters a challenging problem in designing a highly efficient, long durable, non-noble metal-free electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Here, in our work, a two-step hydrothermal reaction was performed to construct a hierarchal NiFe-layer double hydroxide (LDH)/CuS over copper foam for the overall water splitting reaction. While employed the same as an anode material, the designed heterostructure electrode NiFe-LDH/CuS/Cu exhibits excellent OER performance and it demands 249 mV overpotential to reach a current density of 50 mA cm-2 with a lower Tafel slope value of 81.84 mV dec-1. While as a cathode material, the NiFe-LDH/CuS/Cu shows superior HER performance and it demands just 28 mV of overpotential value to reach a current density of 10 mA cm-2 and a lower Tafel slope value of 95.98 mV dec-1. Hence, the NiFe-LDH/CuS/Cu outperforms the commercial Pt/C and RuO2 in terms of activity in HER and OER, respectively. Moreover, when serving as both the cathode and anode catalysts in an electrolyzer for total water splitting, the synthesized electrode only needs a cell potential of 1.55 V versus RHE to reach a current density of 20 mA cm-2 and long-term durability for 25 h in alkaline media. To study the interfacial electron transfer, Mott-Schottky experiments were performed, representing that the electron is transferred from n-type NiFe-LDH to p-type CuS as a result of creating the p-n junction in NiFe-LDH/CuS/Cu. The formation of this p-n junction allows the LDH layer to be more active toward the OH- adsorption and thereby could allow the OER or HER with a less energy input. This work affords another route to a cost effective, highly efficient catalyst toward producing clean energy across the globe.

Enabling and Inducing Oxygen Vacancies in Cobalt Iron Layer Double Hydroxide via Selenization as Precatalysts for Electrocatalytic Hydrogen and Oxygen Evolution Reactions.

Production of hydrogen by water electrolysis is an environment-friendly method and comparatively greener than other methods of hydrogen production such as stream reforming carbon, hydrolysis of metal hydride, etc. However, sluggish kinetics of the individual half-cell reactions hinders the large-scale production of hydrogen. To minimize this disadvantage, finding an appropriate, competent, and low-cost catalyst has attracted attention worldwide. Layer double hydroxide (LDH)-based materials are promising candidates for oxygen evolution reaction (OER) but not fruitful and their hydrogen evolution reaction (HER) activity is very poor, due to the lack of ionic conductivity. The inclusion of chalcogenide and generation of inherent oxygen vacancies in the lattice of LDH lead to improvement of both OER and HER activities. The presence of rich oxygen vacancies was confirmed using both the Tauc plot (1.11 eV, vacancy induction) and the photoluminescence study (peak at 426 nm, photoregeneration of oxygen). In this work, we have developed vacancy-enriched, selenized CoFe-LDH by the consequent wet-chemical and hydrothermal routes, respectively, which was used for OER and HER applications in 1 M KOH and 0.5 M H2SO4 electrolytes, respectively. For OER, the catalyst required only 251 mV overpotential to reach a 50 mA/cm2 current density with a Tafel slope value of 47 mV/dec. For HER, the catalyst demanded only 222 mV overpotential for reaching a 50 mA/cm2 current density with a Tafel slope value of 126 mV/dec. Hence, generating oxygen vacancies leads to several advantages from enhancing the exposed active sites to high probability in obtaining electrocatalytically active species and subsequent assistance in oxygen and hydrogen molecule cleavage.

Electrospun Cobalt-Incorporated MOF-5 Microfibers as a Promising Electrocatalyst for OER in Alkaline Media.

Metal-organic framework (MOF)-based materials have attracted attention in recent times owing to their remarkable properties such as regulatable pore size, high specific surface area, and elasticity in their network topology, geometry, dimension, and chemical functionality. It is believed that the incorporation of a MOF network into a fibrous matrix results in the improvement of the electrocatalytic properties of the material. Herein, we have synthesized a Co-incorporated MOF-5-based fibrous material by a simple wet-chemical method, followed by an electrospinning (ES) process. The as-prepared Co-incorporated MOF-5 microfibers were employed as an electrocatalyst for the oxygen evolution reaction (OER) in 1 M KOH electrolyte. The catalyst demands a lower overpotential of 240 mV to attain a current density of 10 mA/cm2 with a lower Tafel slope value of 120 mV/dec along with a charge transfer resistance value of 2.9 Ω from electron impedance spectroscopy (EIS) analysis. From these results, it has been understood that the incorporation of Co metal into the MOF-5 microfibrous network has significantly improved the OER performance, which made them a potential entrant in other energy-related applications also.

Metallic Gold-Incorporated Ni(OH)2 for Enhanced Water Oxidation in an Alkaline Medium: A Simple Wet-Chemical Approach.

The development of a highly efficient electrocatalyst for the oxygen evolution reaction (OER) with a lower overpotential and high intrinsic activity is highly challenging owing to its sluggish kinetic behavior. As an alternative to the state-of-the-art OER catalyst, recently, transition-metal-based hydroxide materials have been shown to play important roles for the same. Owing to the high earth abundance of various Ni-based hydroxide and its derivatives, these are known to be highly studied materials for the OER. Herein, we report a simple wet-chemical synthesis of metallic gold-incorporated (by varying the concentration of Au3+ ions) Ni(OH)2 nanosheets as an active and stable electrocatalyst for the OER in 1 M KOH medium. The Au-Ni(OH)2 (2) catalyst demanded a low overpotential of 288 mV to attain a geometric current density of 10 mA/cm2 with a lower Tafel value of 55 mV/dec compared to bare Ni(OH)2 with a lower mass loading of only 0.1 mg/cm2. Tafel slope analysis reveals that the incorporation of metallic gold on the hydroxide surfaces could alter the mechanistic pathways of the overall OER reaction. It has been proposed that the incorporation of metallic gold over the Ni(OH)2 surfaces led to a change in the electronic structure of the electroactive nickel sites (Jahn-Teller distortion), which favors the OER by electronic aspects.

Temperature-Controlled Structural Variations of Meticulous Fibrous Networks of NiFe-Polymeric Zeolite Imidazolate Frameworks for Enhanced Performance in Electrocatalytic Water-Splitting Reactions.

Developing non-noble, earth-ample, and stable electrocatalysts are highly anticipated in oxygen-evolution reaction (OER) and hydrogen-evolution reaction (HER) at unique pH conditions. Herein, we have synthesized bimetallic (nickel and iron) zeolite imidazolate framework (ZIF)-based nanofibrous materials via a simple electrospinning (ES) process. The structural stability of the fibrous material is subjected to various calcination conditions. We have elaborated the structural importance of the one-dimensional (1D) fibrous materials in electrocatalytic water-splitting reactions. As a result, NiFe-ZIF-NFs (Nanofibers)-RT (Room Temperature) have delivered a small overpotential of 241 mV at 10 mA cm-2 current density in OER and 290 mV at a fixed current density of 50 mA cm-2 in HER at two different pH conditions with 1 M KOH and 0.5 M H2SO4, respectively. Furthermore, it exposes the actual surface area of 27.270 m2 g-1 and a high electrochemical active surface area (ECSA) of 50 µF in OER and 55 µF in HER, which is responsible for the electrochemical performance with better stability. This exceptional activity of the materials is mainly attributed to the structural dependency of the fibrous network through the polymeric architecture.

Enhancement of the OER Kinetics of the Less-Explored α-MnO2 via Nickel Doping Approaches in Alkaline Medium.

Development of a low-cost transition metal-based catalyst for water splitting is of prime importance for generating green hydrogen on an industrial scale. Recently, various transition metal-based oxides, hydroxides, sulfides, and other chalcogenide-based materials have been synthesized for developing a suitable anode material for the oxygen evolution reaction (OER). Among the various transition metal-based catalysts, their oxides have received much consideration for OER, especially in lower pH condition, and MnO2 is one of the oxides that have widely been used for the same. The large variation in the structural disorder of MnO2 and internal resistance at the electrode-electrolyte interfaces have limited its large-scale application. By considering the above limitations of MnO2, here in this work, we have designed Ni-doped MnO2 via a simple wet-chemical synthetic route, which has been successfully applied for OER application in 0.1 M KOH solution. Doping of various quantities of Ni into the MnO2 lattices improved the OER properties, and for achieving 10 mA/cm2 current density, the Ni-doped MnO2 containing 0.02 M of Ni2+ ions (coined as MnO2-Ni0.002(M)) demands only 445 mV overpotential, whereas the bare MnO2 required 610 mV overpotential. It has been proposed that the incorporation of nickel ions into the MnO2 lattices leads to an electron transfer from the Ni3+ ions to Mn4+, which in turn facilitates the Jahn-Teller distortion in the Mn-O octahedral unit. This electron transfer and the creation of a structural disorder in the Mn sites result in the improvization of the OER properties of the MnO2 materials.

Surface Decoration of DNA-Aided Amorphous Cobalt Hydroxide via Ag+ Ions as Binder-Free Electrodes toward Electrochemical Oxygen Evolution Reaction.

Out of various available methods, generation of hydrogen by electrocatalytic water splitting is the most accepted one which consists of two half-cell reactions, viz, oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction at the cathode. OER is a complex four-electron transfer process, and to sustain the spontaneous generation of hydrogen at the cathode, it is urgent to develop some earth-abundant, low-cost electrode materials. Recently, use of cobalt-based hydroxide as the electrode substrate has taken much consideration and has been fabricated over various substrates. Because of various structural disorders, internal resistance, and dependence on the electrode, the binder substrate makes their applications limited. Here, in this work, to remove structural disorder and to increase electrical conductivity, we have incorporated silver ions into amorphous Co(OH)2, which turns to be a highly active OER electrocatalyst. Also, for the first time, we have developed hydroxide-based materials by using DNA as a stabilizer, and most importantly, using DNA gives an immense opportunity to run long-term OER applications without using an external binder such as nafion. Moreover, for the first time, these DNA-based materials were coated on nickel foam mainly to eliminate the low conductive nature of Ag2O. The synthesized catalyst showed a very high OER activity, and to reach 50 mA/cm2 current density, it needs only 260 mV as overpotential. The amorphous nature of hydroxide-based materials gives a higher opportunity toward the electrolyte to bind on the surface of a catalyst to run the OER with less applied overpotentials.

Nitrogen-Rich Covalent Organic Polymer for Metal-Free Tandem Catalysis and Postmetalation-Actuated High-Performance Water Oxidation.

Development of high-performing catalytic materials for selective and mild chemical transformations through adhering to the principles of sustainability remains a central focus in modern chemistry. Herein, we report the template-free assembly of a thermochemically robust covalent organic polymer (COP: 1) from 2,2'-bipyridine-5,5'-dicarbonyl dichloride and 2,4,6-tris(4-aminophenyl)triazine as [2 + 3] structural motifs. The two-dimensional (2D) layered architecture contains carboxamide functionality, delocalized π-cloud, and free pyridyl-N site-decked pores. Such trifunctionalization benefits this polymeric network exhibiting tandem alcohol oxidation-Knoevenagel condensation. In contrast to common metal-based catalysts, 1 represents a one of a kind metal-free alcohol oxidation reaction via extended π-cloud delocalization-mediated free radical pathway, as comprehensively supported from diverse control experiments. In addition to reasonable recyclability and broad substrate scope, the mild reaction condition underscores its applicability in benign synthesis of valuable product benzylidene malononitrile. Integration of 2,2'-bipyridyl units in this 2D COP favors anchoring non-noble metal ions to devise 1-M (M: Ni2+/ Co2+) that demonstrate outstanding electrochemical oxygen evolution reaction in alkaline media with high chronoamperometric stability. Electrochemical parameters of both 1-Co and 1-Ni outperform some benchmark, commercial, as well as a majority of contemporary OER catalysts. Specifically, the overpotential and Tafel slope (280 mV, 58 mV/dec) for 1-Ni is better than 1-Co (360 mV, 78 mV/dec) because of increased charge accumulation as well as a higher number of active sites compared to the former. In addition, the turnover frequency of 1-Ni is found to be 6 times higher than that of 1-Co and ranks among top-tier water oxidation catalysts. The results provide valuable insights in the field of metal-free tandem catalysis as well as promising electrochemical water splitting at the interface of task-specific functionality fuelling in polymeric organic networks.

2-Aryl-1H-imidazo[4,5-f][1,10]phenanthroline-Based Binuclear Ru(II)/Ir(III)/Re(I) Complexes as Mitochondria Targeting Cancer Stem Cell Therapeutic Agents.

A series of novel Ru(II)/Ir(III)/Re(I)-based organometallic complexes [Ru2L1, Ru2L2, Ir2L1, Ir2L2, Re2L1, and Re2L2] have been synthesized to assess their potency and selectivity against multiple cancer cells A549, HCT-116, and HCT-116 colon CSCs. The cytotoxic screening of the synthesized complexes has revealed that complex Ru2L1 and Ir2L2 are two proficient complexes among all, but Ru2L1 is the most potent complex. A significant binding constant value was observed for DNA and BSA in all complexes. Significant lipophilic properties allow them to penetrate cancer cell membranes, and substantial quantum yield (ϕf) values support bioimaging potential. Again, these complexes are particular for mitochondrial localization and produce a profuse amount of ROS to damage the mitochondrial DNA and then G1 phase cell-cycle arrest. Protein expression analysis unveiled that pro-apoptotic Bax protein overexpressed in Ru2L1-treated cells, whereas antiapoptotic Bcl-2 protein was expressed twofold in Ir2L2-treated cells, which correlated with autophagy reticence.

Morphology Tuning via Linker Modulation: Metal-Free Covalent Organic Nanostructures with Exceptional Chemical Stability for Electrocatalytic Water Splitting.

The development of synthetic routes for the formation of robust porous organic polymers (POPs) with well-defined nanoscale morphology is fundamentally significant for their practical applications. The thermodynamic characteristics that arise from reversible covalent bonding impart intrinsic chemical instability in the polymers, thereby impeding their overall potential. Herein, a unique strategy is reported to overcome the stability issue by designing robust imidazole-linked POPs via tandem reversible/irreversible bond formation. Incorporating inherent rigidity into the secondary building units leads to robust microporous polymeric nanostructures with hollow-spherical morphologies. An in-depth analysis by extensive solid-state NMR (1D and 2D) study on 1H, 13C, and 14N nuclei elucidates the bonding and reveals the high purity of the newly designed imidazole-based POPs. The nitrogen-rich polymeric nanostructures are further used as metal-free electrocatalysts for water splitting. In particular, the rigid POPs show excellent catalytic activity toward the oxygen evolution reaction (OER) with long-term durability. Among them, the most efficient OER electrocatalyst (TAT-TFBE) requires 314 mV of overpotential to drive 10 mA cm-2 current density, demonstrating its superiority over state-of-the-art catalysts (RuO2 and IrO2).

Functionality Modulation Toward Thianthrene-based Metal-Free Electrocatalysts for Water Splitting.

The development of metal-free bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is significant but rarely demonstrated. Porous organic polymers (POPs) with well-defined electroactive functionalities show superior performance in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Precise control of the active sites' local environment requires careful modulation of linkers through the judicious selection of building units. Here, a systematic strategy is introduced for modulating functionality to design and synthesize a series of thianthrene-based bifunctional sp2 C═C bonded POPs with hollow spherical morphologies exhibiting superior electrocatalytic activity. This precise structural tuning allowed to gain insight into the effects of heteroatom incorporation, hydrophilicity, and variations in linker length on electrocatalytic activity. The most efficient bifunctional electrocatalyst THT-PyDAN achieves a current density of 10 mA cm─2 at an overpotential (η10) of ≈65 mV (in 0.5 m H2SO4) and ≈283 mV (in 1 m KOH) for HER and OER, respectively. THT-PyDAN exhibits superior activity to all previously reported metal-free bifunctional electrocatalysts in the literature. Furthermore, these investigations demonstrate that THT-PyDAN maintains its performance even after 36 h of chronoamperometry and 1000 CV cycling. Post-catalytic characterization using FT-IR, XPS, and microscopic imaging techniques underscores the long-term durability of THT-PyDAN.

Melamine-Based Hydrogen-bonded Systems as Organoelectrocatalysts for Water Oxidation Reaction.

Applications of small organic molecules and hydrogen-bonded aggregates, instead of traditional transition-metal-based electrocatalysts, are gaining momentum for addressing the issue of low-cost generation of H2 to power a sustainable environment. Such systems offer the possibility to integrate desired functional moieties with predictive structural repetition for modulating their properties. Despite these advantages, hydrogen-bonded organic systems have largely remained unexplored, especially as electrocatalysts. Melamine and adipic acid-based hydrogen-bonded organic ionic (BMA) and co-crystal systems developed under varying temperatures are explored as electrocatalysts for water oxidation reaction (WOR). These systems are easily modifiable with precisely designed molecular architecture and judiciously positioned nitrogen atoms. Combined effect of charge-assisted hydrogen bonding stabilizes the ionic BMA system under corrosive alkaline conditions and augments its remarkable electrocatalytic WOR activity, achieving a current density of 10 mA cm-2 at an overpotential of 387 mV and Faradaic efficiency ∼94.5 %. The enhanced electrocatalytic ability of BMA is attributed to its hydrophilic nature, unique molecular composition with complementary hydrogen-bonded motifs and a high density of positively charged nitrogen atoms on the surface, that facilitates electrostatic interactions and accelerate charge and mass transport processes culminating in a turnover frequency of ∼0.024 s-1 . This work validates the potential of hydrogen-bonded molecular organo-electrocatalysts towards WOR.