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.

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.

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).

Copper nanoparticle-embellished Zr-based metal-organic framework for electrocatalytic hydrogen evolution reaction.

Copper nanoparticles (Cu NPs) have gained immense popularity in catalysis by virtue of their impressive properties and earth abundance. Herein, we incorporated small-sized copper nanoparticles into the amine-functionalized NU-1000 MOF and used this composite material as an effective catalyst for electrocatalytic Hydrogen Evolution Reaction (HER) studies.

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.

Regulating Surface Charge by Embedding Ru Nanoparticles over 2D Hydroxides toward Water Oxidation.

Exploring highly active and earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is considered one of the prime prerequisites for generating green hydrogen. Herein, a competent microwave-assisted decoration of Ru nanoparticles (NPs) over the bimetallic layered double hydroxide (LDH) material is proposed. The same has been used as an OER catalyst in a 1 M KOH solution. The catalyst shows an interesting Ru NP loading dependency toward the OER, and a concentration-dependent volcanic relationship between electronic charge and thermoneutral current densities has been observed. This volcanic relation shows that with an optimum concentration of Ru NPs, the catalyst could effectively catalyze the OER by obeying the Sabatier principle of ion adsorption. The optimized Ru@CoFe-LDH(3%) demands an overpotential value of only 249 mV to drive a current density value of 10 mA/cm2 with the highest TOF value of 14.4 s-1 as compared to similar CoFe-LDH-based materials. In situ impedance experiments and DFT studies demonstrated that incorporating the Ru NPs boosts the intrinsic OER activity of the CoFe-LDH on account of sufficient activated redox reactivities for both Co and lattice oxygen of the CoFe-LDH. As a result, compared with the pristine CoFe-LDH, the current density of Ru@CoFe-LDH(3%) at 1.55 V vs RHE normalized by ECSA increased by 86.58%. First-principles DFT analysis shows that the optimized Ru@CoFe-LDH(3%) possesses a lower d-band center that indicates weaker and more optimal binding characteristics for OER intermediates, improving the overall OER performance. Overall, this report displays an excellent correlation between the decorated concentration of NPs over the LDH surface which can tune the OER activity as verified by both experimental and theoretical calculations.

Redox-Active and Urea-Engineered-Entangled MOFs for High-Efficiency Water Oxidation and Elevated Temperature Advanced CO2 Separation Cum Organic-Site-Driven Mild-Condition Cycloaddition.

Development of the multifaceted metal-organic framework (MOF) with in situ engineered task-specific sites can promise proficient oxygen evolution reaction (OER) and high-temperature adsorption cum mild-condition fixation of CO2. In fact, effective assimilation of these attributes onto a single material with advance performance characteristics is practically imperative in view of renewable energy application and carbon-footprint reduction. Herein, we developed a three-fold interpenetrated robust Co(II) framework that embraces both redox-active and hydrogen-bond donor moieties inside the microporous channel. The activated MOF demonstrates notable OER catalysis in alkaline medium via quasi-reversible Co2+/Co3+ couple and unveils low overpotential with impressive 53.5 mV/dec Tafel slope that overpowers some benchmark, commercial, as well as contemporary materials. In particular, significantly increased turnover frequency (3.313 s-1 at 400 mV) and fairly low charge-transfer resistance (3.02 Ω) compared to Co3O4, NiO, and majority of redox-active MOFs together with 91% Faradaic efficiency and notable framework durability after multiple OER cycles endorse high-performance water oxidation. Pore-wall decked urea groups benefit appreciable CO2 adsorption even at elevated temperatures with considerable MOF-CO2 interactions and exhibit recurrent capture-release cycles at diverse temperatures. Interestingly, CO2 selectivity displays radical upsurge with temperature rise, affording 40% improved CO2/N2 value of 200 at 313 K, which outperforms many porous adsorbents and delineates real-time CO2 scavenging potential. The guest-free MOF effectively catalyzes solvent-free CO2 cycloaddition with broad substrate tolerance and satisfactory reusability under relatively mild condition. Opposed to the common Lewis acid-mediated reaction, two-point hydrogen-bonding activates the substrate, as supported from controlled experiments, juxtaposing the performance of an un-functionalized MOF and fluorescence modification-derived framework-epoxide interaction, providing valuable insights on unconventional cycloaddition route in the MOF.

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.

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.

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.

Catalytically active silver nanoparticles stabilized on a thiol-functionalized metal-organic framework for an efficient hydrogen evolution reaction.

A post-synthetic technique, Solvent Assisted Ligand Incorporation (SALI), was used for thiol functionalization in the zirconium-based metal-organic framework NU-1000. This thiol-functionalized MOF was employed as a support for the growth of silver nanoparticles (Ag NPs) through coordination of a Ag(I) complex with a node-anchored thiol-ligand, followed by the reduction of Ag(I) to Ag(0). X-ray photoelectron spectroscopy revealed that the ratio of Ag(0) to Ag(I) proportionally increased with the loading of silver ions. The HER activity increased with the enhancement of Ag(0) in the system and the best efficiency was observed for the composite with ∼95% Ag(0). This composite displayed an overpotential of 165 mV in an acidic medium at 10 mA cm-2 and a Tafel slope of 53 mA dec-1. The loading of silver beyond the optimum value led to the aggregation of the particles which affected the overpotential substantially. The catalyst demonstrated appreciable static stability for 24 h, which promotes the use of the material as an HER catalyst. Therefore, these results emphasized that Ag NPs embedded onto a thiol-functionalized MOF is a propitious material for developing a clean and renewable energy source.

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.

Effective Formation of a Mn-ZIF-67 Nanofibrous Network via Electrospinning: An Active Electrocatalyst for OER in Alkaline Medium.

Finding the active center in a bimetallic zeolite imidazolate framework (ZIF) is highly crucial for the electrocatalytic oxygen evolution reaction (OER). In the present study, we constructed a bimetallic ZIF system with cobalt and manganese metal ions and subjected it to an electrospinning technique for feasible fiber formation. The obtained nanofibers delivered a lower overpotential value of 302 mV at a benchmarking current density of 10 mA cm-2 in an electrocatalytic OER study under alkaline conditions. The obtained Tafel slope and charge-transfer resistance values were 125 mV dec-1 and 4 Ω, respectively. The kinetics of the reaction is mainly attributed from the ratio of metals (Co and Mn) present in the catalyst. Jahn-Teller distortion reveals that the electrocatalytic active center on the Mn-incorporated ZIF-67 nanofibers (Mn-ZIF-67-NFs) was found to be Mn3+ along with the Mn2+ and Co2+ ions on the octahedral and tetrahedral sites, respectively, where Co2+ ions tend to suppress the distortion, which is well supported by density functional theory analysis, molecular orbital study, and magnetic studies.

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.

Constructing electrospun spinel NiFe2O4 nanofibers decorated with palladium ions as nanosheets heterostructure: boosting electrocatalytic activity of HER in alkaline water electrolysis.

The development of efficient electrocatalysts for the water splitting process and understanding their fundamental catalytic mechanisms are highly essential to achieving high performance in energy conversion technologies. Herein, we have synthesised spinel nickel ferrite nanofibers (NiFe2O4-NFs) via an electrospinning (ES) method followed by a carbonization process. The resultant fiber was subjected to electrocatalytic water splitting reactions in alkaline medium. The catalytic efficiency of the NiFe2O4-NFs in OER was highly satisfactory. But it is not high enough to catalyse the HER process. Hence, palladium ions were decorated as nanosheets on NiFe2O4-NFs as a heterostructure to improve the catalytic efficiency for HER. Density functional theory (DFT) confirms that the addition of palladium to NiFe2O4-NFs helps to reduce the effect of catalyst poisoning and improve the efficiency of the catalyst. In an alkaline hybrid electrolyser, the required cell voltage was observed as 1.51 V at a fixed current density of 10 mA cm-2.

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.

Incorporating Au11 nanoclusters on MoS2 nanosheet edges for promoting the hydrogen evolution reaction at the interface.

The electrocatalytic hydrogen evolution reaction (HER) holds grip as a promising strategy to obtain renewable energy resources in the form of clean fuel - hydrogen (H2). However, understanding the catalytic mechanism at the atomic level for sustainable and efficient production of hydrogen remains an arduous challenge. In this regard, atomically precise nanoclusters (NCs) with their molecule-like properties can be utilized for a better understanding of the mechanism at the catalytic interface, identification of active sites, and much more. Herein, we report a strategy to enhance the HER activity of the well-known electrocatalyst MoS2 by the incorporation of atomically precise gold nanoclusters, Au11(PPh3)7I3. Interestingly, Au11(PPh3)7I3 NCs were impregnated onto MoS2 nanosheets without protecting ligands as naked Au11 clusters which have increased atom efficiency. Different loadings of Au11(PPh3)7I3 nanoclusters on MoS2 nanosheets revealed the superior HER activity of 2% loading of the NCs. Theoretical calculations have shown that the nanocomposite has the optimum hydrogen adsorption energy that is crucial for efficient H2 production. Combined experimental and theoretical results provide the atomic-level understanding of the utilization of electrochemically dormant ligand-protected NCs to accelerate the HER activity of MoS2 nanosheets.

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.

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.

Revealing the pH-Universal Electrocatalytic Activity of Co-Doped RuO2 toward the Water Oxidation Reaction.

Electrocatalytic water splitting has gained vast attention in recent decades for its role in catalyzing hydrogen production effectively as an alternative to fossil fuels. Moreover, the designing of highly efficient oxygen evolution reaction (OER) electrocatalysts across the universal pH conditions was more challengeable as in harsh anodic potentials, it questions the activity and stability of the concerned catalyst. Generally, geometrical engineering and electronic structural modulation of the catalyst can effectively boost the OER activity. Herein, a Co-doped RuO2 nanorod material is developed and used as an OER electrocatalyst at different pH conditions. Co-RuO2 exhibits a lower overpotential value of 238 mV in an alkaline environment (1 M KOH) with a Tafel slope value of 48 mV/dec. On the other hand, in acidic, neutral, and near-neutral environments, it required overpotentials of 328, 453, and 470 mV, respectively, to attain a 10 mA/cm2 current density. It is observed that doping of Co into the RuO2 could synergistically increase the active sites with the enhanced electrophilic nature of Ru4+ to accelerate OER in all of the pH ranges. This study finds the applicability of earth-abundant-based metals like Co to be used in universal pH conditions with a simple doping technique. Further, it assured the stable nature in all pH electrolytes and needs to be further explored with other metals in the future.