Organic-Inorganic Hybrid Crystal-Assisted Etching of Nickel Foam for the Collectively Exhaustive Electrochemical Performance of Oxygen Evolution Reaction.

In this work, an organic-inorganic hybrid crystal, violet-crystal (VC), was used to etch the nickel foam (NF) to fabricate a self-standing electrode for the water oxidation reaction. The efficacy of VC-assisted etching manifests the promising electrochemical performance towards the oxygen evolution reaction (OER), requiring only ~356 and ~376 mV overpotentials to reach 50 and 100 mA cm-2 , respectively. The OER activity improvement is attributed to the collectively exhaustive effects arising from the incorporation of various elements in the NF, and the enhancement of active site density. Furthermore, the self-standing electrode is robust, exhibiting a stable OER activity after 4,000 cyclic voltammetry cycles, and ~50 h. The anodic transfer coefficients (αa ) show that the first electron transfer step is the rate-determining step on the surface of NF-VCs-1.0 (NF etched by 1 g of VCs) electrode, while the chemical step involving dissociation following the first electron transfer step is identified as the rate-limiting step in other electrodes. The lowest Tafel slope value observed in the NF-VCs-1.0 electrode indicates the high surface coverage of oxygen intermediates and more favorable OER reaction kinetics, as confirmed by high interfacial chemical capacitance and low charge transport/interfacial resistance. This work demonstrates the importance of VCs-assisted etching of NF to activate the OER, and the ability to predict reaction kinetics and rate-limiting step based on αa values, which will open new avenues to identify advanced electrocatalysts for the water oxidation reaction.

Ferrocene-Incorporated Cobalt Sulfide Nanoarchitecture for Superior Oxygen Evolution Reaction.

Here, ferrocene(Fc)-incorporated cobalt sulfide (Cox Sy ) nanostructures directly grown on carbon nanotube (CNT) or carbon fiber (CF) networks for electrochemical oxygen evolution reaction (OER) using a facile one-step solvothermal method are reported. The strong synergistic interaction between Fc-Cox Sy nanostructures and electrically conductive CNTs results in the superior electrocatalytic activity with a very small overpotential of ≈304 mV at 10 mA cm-2 and a low Tafel slope of 54.2 mV dec-1 in 1 m KOH electrolyte. Furthermore, the Fc-incorporated Cox Sy (FCoS) nanostructures are directly grown on the acid pretreated carbon fiber (ACF), and the resulting fabricated electrode delivers excellent OER performance with a low overpotential of ≈315 mV at 10 mA cm-2 . Such superior OER catalytic activity can be attributed to 3D Fc-Cox Sy nanoarchitectures that consist of a high concentration of vertical nanosheets with uniform distribution of nanoparticles that afford a large number of active surface areas and edge sites. Besides, the tight contact interface between ACF substrate and Fc-Cox Sy nanostructures could effectively facilitate the electron transfer rate in the OER. This study provides valuable insights for the rational design of energy storage and conversion materials by the incorporation of other transition metal into metal sulfide/oxide nanostructures utilizing metallocene.

Enhanced Superhydrophobic Performance of BN-MoS2 Heterostructure Prepared via a Rapid, One-Pot Supercritical Fluid Processing.

Fabrication of highly crystalline BN-MoS2 heterostructure with >95% yield was demonstrated using one-pot supercritical fluid processing within 30 min. The existence of 20-50 layers of BN-MoS2 in the prepared heterostructure was confirmed by AFM analysis. The HR-TEM imaging and mapping analysis revealed the well-melded BN and MoS2 nanosheets in the heterostructure. The drastic reduction in XRD line intensities corresponding to the (002) plane and broadening of the peaks for the BN system over MoS2 indicated the effective exfoliation and lateral size reduction in BN nanosheets during SCF processing. Also, the exfoliated MoS2 nanosheets are preferentially exposed rather than BN nanosheets; consequently, the MoS2 nanosheets sturdily covered BN nanosheets in the heterostructure. The exfoliated BN and MoS2 nanosheets with nanoscale roughness make the surface highly hydrophobic in nature. As a result, the BN-MoS2 heterostructure showed superior superhydrophobic performance with high water contact angle of 165.9°, which is much higher than the value reported in the literature.

Boosting Oxygen Evolution Reaction on Metallocene-based Transition Metal Sulfides Integrated with N-doped Carbon Nanostructures.

In this study, utilizing metallocene and organosulfur chelating agent, an innovative synthetic route was developed towards electrochemically activated transition metal sulfides entrapped in pyridinic nitrogen-incorporated carbon nanostructures for superior oxygen evolution reaction (OER). Most importantly, the preferential electrochemical activation process, which consisted of both anodic and cathodic pre-treatment steps, strikingly enhanced OER and long-lasting cyclic stability. The substantial increase in OER electrocatalytic activity of Ni9 S8 /Ni3 S2 -NC and Co9 S8 -NC during the activation process was mainly attributed to the increase of faradaic active site density on the catalytic layer resulting from the reconstruction of catalytic interfaces. It was also found that Fe-based metallocene [ferrocene (Fc)]-incorporation in the Co9 S8 -NC and Ni9 S8 /Ni3 S2 -NC nanostructures significantly boosted the OER activity. Thus, the combined effects of Fc-incorporation and the electrochemical activation process reduced the overpotential to about 115 and 95 mV on the Ni9 S8 /Ni3 S2 -NC and Co9 S8 -NC nanostructures to derive a current density of 10 mA cm-2 , respectively. Notably, Fc-Ni9 S8 /Ni3 S2 -NC electrocatalysts required very small overpotentials of around 222, 244, and 280 mV to acquire the current densities of 10, 20, and 50 mA cm-2 , respectively. This work opens up a new avenue for superior OER electrocatalysts by the utilization of metallocene and the preferential electrochemical activation process.

A dual-ion accepting vanadium carbide nanowire cathode integrated with carbon cloths for high cycling stability.

Herein, we report vanadium carbide (V8C7) nanowires (NWs) axially grown on carbon cloths (CCs) as a dual-ion accepting cathode for both lithium (LIBs) and sodium-ion batteries (SIBs). Using a facile hydrothermal method, we grew V2O3 NWs on CCs and subsequently reduced them to V8C7 by annealing with carbon sources under a H2/Ar atmosphere. In striking contrast to V2O5 NW cathodes obtained by annealing under air, the V8C7 NWs exhibit outstanding cycling stability during 500 cycles, and good rate capability for both LIBs and SIBs. V8C7 NWs as cathode active materials for LIBs exhibited 203.9 mA h g-1 specific capacity at 0.1 C after 500 cycles, 91.12% cycling retention and a coulombic efficiency of 99.84%. As cathodes in SIBs, the V8C7 NWs delivered 176.34 mA h g-1 specific capacity at 0.1 C during 300 cycles. Their defect sites by removal of the oxygen framework in V2O3 NWs have a high surface area (183.27 m2 g-1) and the unique 1D NW structure highly mitigates the volume changes during charge and discharge showing a superior electrochemical performance. Compared to commercially available cathodes, V8C7 nanowires have very good cycling stability and enhanced electrical conductivity. Moreover, the synergistic effect with 3D CCs utilized here as a current collector provides a large number of cation-accessible active sites in conjunction with high electrical conductivity and chemical stability.

Supercritical water assisted preparation of recyclable gold nanoparticles and their catalytic utility in cross-coupling reactions under sustainable conditions.

Preparation of gold nanoparticles (AuNPs) in environmentally friendly water without using any reducing agents under supercritical conditions is demonstrated. PXRD, XPS, FE-SEM and HR-TEM analysis confirmed the formation of phase-pure and crystalline AuNPs of the size of ∼10-30 nm. The catalytic potential of AuNPs was manifested through a generalized green procedure that could accommodate both Sonogashira as well as Suzuki coupling under aqueous conditions at low catalytic loading (0.1 mol%). The AuNP catalyst was found to be recuperated after the reaction and reused for up to six catalytic cycles with no leaching out of gold species as confirmed through ICP-OES analysis. With no confinement of AuNP catalysis to cross-coupling reaction, synthetic extension to one-flask preparation of π-conjugated semiconductors (4 examples) and their optoelectronic properties were also investigated. Other significant features of the present work include short reaction time, site-selectivity, wide substrate scope, high conversion, good chemical yields and applicability in gram-scale synthesis. Overall, the results of this paper signify an operationally sustainable supercritical fluid processing method for the synthesis of AuNPs and their catalytic application towards cross-coupling reactions in green media.

Electrochemical cycling and beyond: unrevealed activation of MoO3 for electrochemical hydrogen evolution reactions.

We demonstrate electrochemical cycling-induced reduction of MoO3 to monoclinic molybdenum dioxide and molybdenum sub-oxides (MoO3-x), which exhibit excellent electrochemical hydrogen evolution reaction (HER) activity. The conversion of MoO3 during cycling was probed; after 250 cycles, the redox peaks were found to diminish with an onset potential shift and increased HER current density. At 400 cycles, the insertion/deinsertion processes observed in the initial cycles are completely absent and the HER current density is enhanced to the maximum. The effect of MoO3 morphology and size on the electrochemical reduction of MoO3 was also studied.

Supercritical Fluid Facilitated Disintegration of Hexagonal Boron Nitride Nanosheets to Quantum Dots and Its Application in Cells Imaging.

Preparation of quantum dots (QDs) and exfoliation of two-dimensional layered materials have gathered significant attention in recent days. Though, there are number of attempts have been reported, facile and efficient methodology is yet to be explored. Here, we demonstrate supercritical fluid processing approach for rapid and facile synthesis of blue luminescent BN QDs from layered bulk material via in situ exfoliation followed by disintegration. The microscopic and AFM analysis confirmed the few layer BN QDs formation. The strong luminescent behavior of BN QDs is utilized to stain Gram-negative bacterial cells specifically in the presence of Gram-positive bacterial cells.