Electrocatalytic Performance of 2D Monolayer WSeTe Janus Transition Metal Dichalcogenide for Highly Efficient H2 Evolution Reaction.

Nowadays, the development of clean and green energy sources is the priority interest of research due to increasing global energy demand and extensive usage of fossil fuels, which create pollutants. Hydrogen has the highest energy density by weight among all chemical fuels. For the commercial-scale production of hydrogen, water electrolysis is the best method, which requires an efficient, cost-effective, and earth-abundant electrocatalyst. Recent studies have shown that the 2D Janus transition metal dichalcogenides (JTMDs) are promising materials for use as electrocatalysts and are highly effective for electrocatalytic H2 evolution reaction (HER). Here, we report a 2D monolayer WSeTe JTMD, which is highly effective toward HER. We have studied the electronic properties of 2D monolayer WSeTe JTMD using the periodic hybrid DFT-D method, and a direct electronic band gap of 2.39 eV was obtained. We have explored the HER pathways, mechanisms, and intermediates, including various transition state (TS) structures (Volmer TS, i.e., H*-migration TS, Heyrovsky TS, and Tafel TS) using a molecular cluster model of the subject JTMD noted as W10Se9Te12. The present calculations reveal that the 2D monolayer WSeTe JTMD is a potential electrocatalyst for HER. It has the lowest energy barriers for all the TSs among other TMDs. It has been shown that the Heyrovsky energy barrier (= 8.72 kcal mol-1) in the case of the Volmer-Heyrovsky mechanism is larger than the Tafel energy barrier (= 3.27 kcal mol-1) in the Volmer-Tafel mechanism. Hence, our present study suggests that the formation of H2 is energetically more favorable via the Volmer-Tafel mechanism. This study helps to shed light on the rational design of 2D single-layer JTMD, which is highly effective toward HER, and we expect that the present work can be further extended to other JTMDs to find out the improved electrocatalytic performance.

Illuminating the Role of Mo Defective 2D Monolayer MoTe2 toward Highly Efficient Electrocatalytic O2 Reduction Reaction.

The fuel cell is one of the solutions to current energy problems as it comes under green and renewable energy technology. The primary limitation of a fuel cell lies in the relatively slow rate of oxygen reduction reactions (ORR) that take place on the cathode, and this is an all-important reaction. An efficient electrocatalyst provides the advancement of green energy-based fuel cell technology, and it can speed up the ORR process. The present work provides the study of non-noble metal-based electrocatalyst for ORR. We have computationally designed a 3 × 3 supercell model of metal defective (Mo-defective) MoTe2 transition metal dichalcogenide (TMD) material to study its electrocatalytic activity toward ORR. This work provides a comprehensive analysis of all reaction intermediates that play a role in ORR on the surfaces of metal-deficient MoTe2. The first-principles-based dispersion-corrected density functional theory (in short DFT-D) method was implemented to analyze the reaction-free energies (ΔG) for each ORR reaction step. The present study indicates that the ORR on the surface of metal-defective MoTe2 follows the 4e- transfer mechanism. This study suggests that the 2D Mo-defective MoTe2 TMD has the potential to be an effective ORR electrocatalyst in fuel cells.

Nanostructured Pt-doped 2D MoSe2: an efficient bifunctional electrocatalyst for both hydrogen evolution and oxygen reduction reactions.

Two-dimensional transition metal dichalcogenides (TMDs) are a new family of 2D materials with features that make them appealing for potential applications in nanomaterials science and engineering. Recently, these 2D TMDs have attracted significant research interest because of the abundant choice of materials with diverse and tunable electronic, optical, chemical, and electrocatalytic properties. Although, the edges of the 2D TMDs show excellent electrocatalytic performance, their basal plane (001) is inert, which hinders their industrial applications for electrocatalysis. Transition metal/chalcogen atom vacancies or doping with some other foreign atoms may be a remedy to activate the inert basal plane. Here, we have computationally designed 2D monolayer MoSe2 and studied its electronic properties with electrocatalytic activities. A Pt-atom has been doped in the pristine 2D MoSe2 (i.e., Pt-MoSe2) to activate the inert basal plane resulting in a zero band gap. This study reveals that the Pt-MoSe2 is an excellent bifunctional electrocatalyst for both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) with the aid of first priciples-based hybrid density functional theory (DFT). The periodic hybrid DFT method has been applied to compute the electronic properties of both the pristine MoSe2 and Pt-MoSe2. To determine both the HER and ORR mechanisms on the surface of the Pt-MoSe2 material, non-periodic DFT calculation has been performed by considering a molecular Pt1-Mo9Se21 cluster model. The present study shows that the 2D Pt-MoSe2 follows the Volmer-Heyrovsky mechanism for the HER with energy barriers of about 9.29 kcal mol-1 and 10.55 kcal mol-1 during the H˙-migration and Heyrovsky reactions. The ORR is achieved by a four-electron transfer mechanism with the formation of two transition energy barriers of about 14.94 kcal mol-1 and 11.10 kcal mol-1, respectively. The lower energy barriers and high turnover frequency during the reactions expose that the Pt-MoSe2 can be adopted as an efficient bifunctional electrocatalyst for both the HER and ORR. The present studies demonstrate that the exceptional HER and ORR activity and stability performance shown by the MoSe2 electrocatalyst can be enhanced by Pt-doping, opening a promising concept for the sensible design of high-performance catalysts for H2 production and O2 reduction.

Elucidating the oxygen reduction reaction mechanism on the surfaces of 2D monolayer CsPbBr3 perovskite.

The oxygen reduction reaction (ORR) is an indispensable reaction in electrochemical energy converting systems such as fuel cells. Generally, reaction kinetics of the ORR is slow, and to speed it up, a practical electrocatalyst is needed. Pt-based catalysts are thermodynamically more appropriate, but due to their scarcity and high cost, they cannot be used on a commercial scale in industries. To search for non-noble metal catalysts, we have performed a theoretical study on the CsPbBr3 perovskite material as a potential candidate for the ORR. The 3D bulk crystal structure of CsPbBr3 shows a large electronic band gap (Eg) of around 2.95 eV and it cannot be used as an efficient electrocatalyst for the ORR. We have cleaved a (001) surface from the 3D CsPbBr3 perovskite and computationally designed a 2D monolayer slab structure of the CsPbBr3 material. The present study showed that the 2D monolayer structure of CsPbBr3 has a tiny band gap about 0.22 eV, and hence the 2D monolayer CsPbBr3 perovskite can be used as a cathode material for fuel cell applications. Special priority has been given to the 2D layered perovskite structure to gain insights into its ORR kinetics by employing the first principles-based density functional theory (DFT) method. This study reveals that the basal plane of the 2D CsPbBr3 perovskite exhibits excellent electrocatalytic activity toward the ORR with a four-electron reduction pathway selectivity. Both the dissociative and associative reaction mechanisms of the ORR on the surfaces of the 2D monolayer CsPbBr3 perovskite have been explored by computing the change in Gibb's free energy (ΔG). All the reaction intermediates studied here are thermodynamically favorable and the present study suggests that the ORR follows a 4e- transfer mechanism on the surface of 2D CsPbBr3 and the associative mechanism is favorable over the dissociative mechanism of the ORR. This study provides a theoretical basis for future application of 2D CsPbBr3 perovskite-based electrocatalysts for achieving an effective ORR, indicating that they are promising Pt-free candidates for fuel cell components.

Unveiling the role of 2D monolayer Mn-doped MoS2 material: toward an efficient electrocatalyst for H2 evolution reaction.

Two-dimensional (2D) monolayer pristine MoS2 transition metal dichalcogenide (TMD) is the most studied material because of its potential applications as nonprecious electrocatalyst for the hydrogen evolution reaction (HER). Previous studies have shown that the basal planes of 2D MoS2 are catalytically inert, and hence it cannot be used directly in desired applications such as electrochemical HER in industry. Here, we thoroughly studied a defect-engineered Mn-doped 2D monolayer MoS2 (Mn-MoS2) material, where Mn was doped in pristine MoS2 to activate its inert basal planes. Using the density functional theory (DFT) method, we performed rigorous inspection of the electronic structures and properties of the 2D monolayer Mn-MoS2 as a promising alternative to noble metal-free catalyst for effective HER. A periodic 2D slab of monolayer Mn-MoS2 was created to study the electronic properties (such as band gap, band structures and total density of states (DOS)) and the reaction pathways occurring on the surface of this material. The detailed HER mechanism was explored by creating an Mn1Mo9S21 non-periodic finite molecular cluster model system using the M06-L DFT method including solvation effects to determine the reaction barriers and kinetics. Our study revealed that the 2D Mn-MoS2 follows the most favorable Volmer-Heyrovsky reaction mechanism with a very low energy barrier during H2 evolution. It was found that the change in the free energy barrier (ΔG) during the H˙-migration (i.e., Volmer) and Heyrovsky reactions is about 10.34-10.79 kcal mol-1 (computed in the solvent phase), indicating that this material is an exceptional electrocatalyst for the HER. The Tafel slope (y) was lower in the case of the 2D monolayer Mn-MoS2 material due to the overlap of the s-orbital of hydrogen and d-orbitals of the Mn atoms in the HOMO and LUMO transition states (TS1 and TS2) of both the Volmer and Heyrovsky reaction steps, respectively. The better stabilization of the atomic orbitals in the HER rate-limiting step Heyrovsky TS2 is the key for reducing the reaction barrier, and thus the overall catalysis, indicating a better electrocatalytic performance for H2 evolution. This study focused on designing low-cost and efficient electrocatalysts for the HER using earth abundant transition metal dichalcogenides (TMDs) and decreasing the activation energy barriers by scrutinizing the kinetics of the reaction to achieve high reactivity.

Sonication-Induced Boladipeptide-Based Metallogel as an Efficient Electrocatalyst for the Oxygen Evolution Reaction.

Bioinspired, self-assembled hybrid materials show great potential in the field of energy conversion. Here, we have prepared a sonication-induced boladipeptide (HO-YF-AA-FY-OH (PBFY); AA = Adipic acid, F = l-phenylalanine, and Y = l-tyrosine) and an anchored, self-assembled nickel-based coordinated polymeric nanohybrid hydrogel (Ni-PBFY). The morphological studies of hydrogels PBFY and Ni-PBFY exhibit nanofibrillar network structures. XPS analysis has been used to study the self-assembled coordinated polymeric hydrogel Ni-PBFY-3, with the aim of identifying its chemical makeup and electronic state. XANES and EXAFS analyses have been used to examine the local electronic structure and coordination environment of Ni-PBFY-3. The xerogel of Ni-PBFY was used to fabricate the electrodes and is utilized in the OER (oxygen evolution reaction). The native hydrogel (PBFY) contains a gelator boladipeptide of 15.33 mg (20 mmol L-1) in a final volume of 1 mL. The metallo-hydrogel (Ni-PBFY-3) is prepared by combining 15.33 mg (20 mmol L-1) of boladipeptide (PBFY) with 3 mg (13 mmol L-1) of NiCl2·6H2O metal in a final volume of 1 mL. It displays an ultralow Tafel slope of 74 mV dec-1 and a lower overpotential of 164 mV at a 10 mA cm-2 current density in a 1 M KOH electrolyte, compared to other electrocatalysts under the same experimental conditions. Furthermore, the Ni-PBFY-3 electrocatalyst has been witnessed to be highly stable during 100 h of chronopotentiometry performance. To explore the OER mechanism in an alkaline medium, a theoretical calculation was carried out by employing the first-principles-based density functional theory (DFT) method. The computed results obtained by the DFT method further confirm that the Ni-PBFY-3 electrocatalyst has a high intrinsic activity toward the OER, and the value of overpotential obtained from the present experiment agrees well with the computed value of the overpotential. The biomolecule-assisted electrocatalytic results provide a new approach for designing efficient electrocatalysts, which could have significant implications in the field of green energy conversion.

Pyrene-based fluorescent Ru(II)-arene complexes for significant biological applications: catalytic potential, DNA/protein binding, two photon cell imaging and in vitro cytotoxicity.

Ruthenium complexes are being studied extensively as anticancer drugs following the inclusion of NAMI-A and KP1019 in phase II clinical trials for the treatment of metastatic phase and primary tumors. Herein, we designed and synthesized four organometallic Ru(II)-arene complexes [Ru(η6-p-cymene)(L)Cl] (1), [Ru(η6-benzene)(L)Cl] (2), [Ru(η6-p-cymene)(L)N3] (3) and [Ru(η6-benzene)(L)N3] (4) [HL = (E)-N'-(pyren-1-ylmethylene)thiopene-2-carbohydrazide] that have anticancer, antimetastatic and two-photon cell imaging abilities. Moreover, in the transfer hydrogenation of NADH to NAD+, these compounds also display good catalytic activity. All the complexes, 1-4, are well characterized by spectroscopic techniques (NMR, mass, FTIR, UV-vis and fluorescence). The single crystal X-ray diffraction technique proved that the ligand L coordinates through an N,O-bidentate chelating fashion in the solid-state structures of complexes 1 and 2. The stability study of the complexes was performed through UV-visible spectroscopy. The cytotoxicities of all the complexes were screened through MTT assay and the results revealed that the complexes have potential anticancer activity against various cancerous cells (HeLa, MCF7 and A431). Studies with spectroscopic techniques revealed that complexes 1-4 exhibit strong interactions with biological molecules i.e. proteins (HSA and BSA) and CT-DNA. The density functional theory (DFT-D) method has been employed in the present study to know the interaction between DNA and complexes by calculating the HOMO and LUMO energy. A plausible mechanism for NADH oxidation has also been explored and the DFT calculations are found to be in accord with the experimental observation. Furthermore, we have investigated intracellular reactive oxygen species (ROS) generation capabilities in the MCF7 breast cancer cell line. The Hoechst/PI dual staining method confirmed the apoptosis mode of cell death. Meanwhile, complexes 1-4 show capabilities to prevent the metastasis phase of cancer cells by inhibiting cell migration.

Aging-Responsive Phase Transition of VOOH to V10O24·nH2O vs Zn2+ Storage Performance as a Rechargeable Aqueous Zn-Ion Battery Cathode.

Vanadium oxyhydroxide has been recently investigated as a starting material to synthesize different phases of vanadium oxides by electrochemical or thermal conversion and has been used as an aqueous zinc-ion battery (AZIB) cathode. However, the low-valent vanadium oxides have poor phase stability under ambient conditions. So far, there is no study on understanding the phase evolution of such low-valent vanadium oxides and their effect on the electrochemical performance toward hosting the Zn2+ ions. The primary goal of the work is to develop a high-performance AZIB cathode, and the highlight of the current work is the insight into the auto-oxidation-induced phase transition of VOOH to V10O24·nH2O under ambient conditions and Zn2+ intercalation behavior thereon as an aqueous zinc-ion battery cathode. Herein, we demonstrate that hydrothermally synthesized VOOH undergoes a phase transition to V10O24·nH2O during both the electrochemical cycling and aerial aging over 38-45 days. However, continued aging till 150 days at room temperature in an open atmosphere exhibited an increased interlayer water content in the V10O24·nH2O, which was associated with a morphological change with different surface area/porosity characteristics and notably reduced charge transfer/diffusion resistance as an aqueous zinc-ion battery cathode. Although the fresh VOOH cathode had impressive specific capacity at rate performance, (326 mAh/g capacity at 0.1 A/g current and 104 mAh/g capacity at 4 A/g current) the cathode suffered from a continuous capacity decay. Interestingly, the aged VOOH electrodes showed gradually decreasing specific capacity with aging at low current and however followed the reverse order at high current. At a comparable specific power of ∼64-66 W/kg, the fresh VOOH and aged VOOH after 60, 120, and 150 days of aging showed the respective energy densities of 208.3, 281.2, 269.2, and 240.6 Wh/kg. Among all the VOOH materials, the 150 day-aged VOOH cathode exhibited the highest energy density at a power density beyond 1000 W/kg. Thanks to the improved kinetics, the 150 day-aged VOOH cathode delivered a considerable energy density of 39.7 Wh/kg with a high specific power of 4466 W/kg. Also, it showed excellent cycling performance with only 0.002% capacity loss per cycle over 20 300 cycles at 10 A/g.