Catalytic Activity In Reaction Research Articles

NiMn2O4-based Ni-Mn bimetallic oxides as electrocatalysts for the oxygen reduction reaction in Al–air batteries

To date, research on air battery catalysts has been mainly focused on finding materials with a high oxygen reduction reaction (ORR) catalytic activity. However, the high cost of platinum catalysts restricts their commercialization. Herein, we report a simple hydrothermal-calcination method to fabricate low-cost NiMn2O4 -based Ni-Mn bimetallic oxides. The Ni-Mn-600 sample showed a high onset potential (1.01 V vs. RHE), which was more positive than that for 20 wt% Pt/C (0.97 V vs. RHE), and its half-wave potential (0.78 V vs. RHE) was comparable to that for 20 wt% Pt/C (0.84 V vs. RHE). Moreover, Ni-Mn-600 as an Al-air battery air–cathode catalyst exhibited a high discharge plateau of 1.42 V and peak power density of 100.45 mW cm−2, which outperformed those for 20 wt% Pt/C (1.34 V and 76.10 mW cm−2). The high ORR electrocatalytic activity of Ni-Mn-600 may be attributed to the nanorod morphology and high ratio of (Mn3++Mn4+)/Mn2+ and Ni3+/Ni2+. This work demonstrated that NiMn2O4-based Ni-Mn bimetallic oxides as cathode catalysts have good research prospects in aluminum-air batteries and other energy applications.

Modifying the electrochemical process of Li–O2 battery by integrated NiMn-layered double hydroxides substrate

As typical two-dimension material, layered double hydroxides (LDHs) attract great interest and are believed to be promising catalysts in Li–O2 battery due to their facile tunability of composition, structures and properties. However, the low electric conductivity and limited catalytic active site exposure caused by the large particle size and severe lamella stacking are the main challenges. Herein, an interconnected, highly active and ultra-thin NiMn-LDHs is deposited on 3D Ni foam and used as integrated porous catalyst substrate (NiMn-LDHs substrate), the NiMn-LDHs substrate is functional as both current collector and catalyst layer, and the NiMn-LDHs substrate exhibits high catalytic activity and robust stability, the substrate successfully plays the function of tunning the electrochemical process of Li–O2 battery. The Li–O2 battery uses this kind of substrate exhibits much improved discharge capacity and long cycle performance compared with pristine Ni substrate. The benefit of the porous NiMn-LDHs in improving the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activities is also supported by rotating disc electrode techniques. This work highlights the strategy of fabricating high efficient LDHs catalyst and provides a new direction for achieving highly efficient integrated catalytic cathode for practical use.

Influence of the nature of IB group metals on catalytic activity in reactions of homomolecular hydrogen exchange on Cu, Ag, Au nanoparticles

In contrast to bulk metals, the nanoparticles of copper, silver and gold catalyze the low-temperature reaction of ortho-para conversion of protium (the physical magnetic mechanism) which indicates the presence of magnetic properties in nanoparticles of metals of the IB group. Catalytic activity depends on the nature of the metal: Au > Ag > Cu. Copper nanoparticles are unstable, their catalytic activity decreases over time. Gold and silver nanoparticles are stable.The deutero‑hydrogen exchange reaction proceeds on silver and gold nanoparticles by the chemical mechanism. In copper nanoparticles, no H2-D2 exchange activity was observed.

Functional interactions of adrenodoxin with several human mitochondrial cytochrome P450 enzymes

Seven of the 57 human cytochrome P450 (P450) enzymes are mitochondrial and carry out important reactions with steroids and vitamins A and D. These seven P450s utilize an electron transport chain that includes NADPH, NADPH-adrenodoxin reductase (AdR), and adrenodoxin (Adx) instead of the diflavin NADPH-P450 reductase (POR) used by the other P450s in the endoplasmic reticulum. Although numerous studies have been published involving mitochondrial P450 systems, the experimental conditions vary considerably. We compared human Adx and bovine Adx, a commonly used component, and found very similar catalytic activities in reactions catalyzed by human P450s 11B2, 27A1, and 27C1. Binding constants of 6–200 nM were estimated for Adx binding to these P450s using microscale thermophoresis. All P450 catalytic reactions were saturated at 10 μM Adx, and higher concentrations were not inhibitory up to at least 50 μM. Collectively these studies demonstrate the tight binding of Adx (both human and bovine) to AdR and to several mitochondrial P450s and provide guidance for optimization of Adx-dependent P450 reactions.

Palladium Catalysts Based on Porous Aromatic Frameworks, Modified with Ethanolamino-Groups, for Hydrogenation of Alkynes, Alkenes and Dienes

The current work describes an attempt to synthesize hybrid materials combining porous aromatic frameworks (PAFs) and dendrimers and use them to obtain novel highly active and selective palladium catalysts. PAFs are carbon porous materials with rigid aromatic structure and high stability, and the dendrimers are macromolecules which can effectively stabilize metal nanoparticles and tune their activity in catalytic reactions. Two porous aromatic frameworks, PAF-20 and PAF-30, are modified step-by-step with diethanolamine and hydroxyl groups at the ends of which are replaced by new diethanolamine molecules. Then, palladium nanoparticles are applied to the synthesized materials. Properties of the obtained materials and catalysts are investigated using X-ray photoelectron spectroscopy, transmission electron microscopy, solid state nuclear magnetic resonance spectroscopy, low temperature N2 adsorption and elemental analysis. The resulting catalysts are successfully applied as an efficient and recyclable catalyst for selective hydrogenation of alkynes to alkenes at very high (up to 90,000) substrate/Pd ratios.

Oxygen Reduction Reaction Catalytic Activities of Pure Ni-Based Perovskite-Related Structure Oxides

Complex transition-metal oxides offer an interesting class of materials for use as oxygen reduction reaction (ORR) catalysts. A recent study proposed a volcano-shape relationship between ORR activi...

Highly porous metal organic framework derived NiO hollow spheres and flowers for oxygen evolution reaction and supercapacitors

In this study, metal-organic-framework (MOF) derived porous NiO hollow spheres and flowers were obtained using facile solvothermal synthesis and heat treatment. After pyrolyzing, the flower like and hollow spherical like morphology of NiO nanoparticles was successfully inherited from the initial MOF-based templates. The electrochemical studies demonstrated that the porous NiO hallow spheres unveiled a better supercapacitive performance (specific capacitance (Cs) = 1058 F g−1 at current density (j) = 2 A g−1) and oxygen evolution reaction (OER) catalytic activity (overpotential (ɳ) = 323 mV) compared to porous NiO flowers (Cs = 857 F g−1 at j = 2 A g−1 and ɳ = 346 mV). Moreover, excellent capacity retention of over 93% was obtained in porous NiO-hs nanoparticles even after 5000 cycles. The fabricated NiO//Fe2O3 asymmetric supercapacitor delivered an energy density (E) of 35.75 W h Kg−1 under power density (P) of 780 W kg−1 and showed promising stability over 3000 cycles. Considering the ease of preparation and high catalytic activity and supercapacitive performance, these prous NiO hallow structures can be considered as a potential electrode material for next generation energy storage devices and OER catalysts.

A-site deficient perovskite nanofibers boost oxygen evolution reaction for zinc-air batteries

Among the various perovskites, Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) has been theoretically proved to have the prominent intrinsic oxygen evolution reaction (OER) catalytic activity in the alkaline solutions. Whereas, most of the measured bulk BSCF samples suffer the unsatisfactory OER activities which are much more inferior than that of the state-of-the-art catalyst of IrO2. In this work, we synthesize the A-site deficient BSCF nanofibers with the diameter of 300 nm by electrospinning for the first time. Thanks to the one dimensional (1D) nanofiber structure and A-site deficiency, the optimized BSCF nanofibers (BSCF-80-ES) demonstrate the remarkably enhanced OER activity with a low potential of 1.54 V at 10 mA cm−2 in 1 M KOH and an improved oxygen reduction reaction (ORR) activity. It is noteworthy that the OER potential of BSCF-80-ES keeps almost unchanged during the long-term test, indicating an excellent OER stability. Moreover, BSCF-80-ES with the high bifunctional catalytic activity and superb stability can be used as a promising oxygen catalyst for aqueous and flexible solid-state zinc-air batteries.

Dynamic structure evolution of free-standing S-doped porous Co-Fe microspheres with enhanced oxygen evolution electrocatalysis in alkaline media

Herein, S-doped Co-Fe hybrid films with unique 3D porous microsphere arrays stacked by ultrathin nanoflakes directly grown on nickel foam (Co-Fe-S NFs@MS/NF) are synthesized via a single-step co-electrodeposition strategy. The synergistic effects among Fe, S and Co enable superior oxygen evolution reaction (OER) catalytic activity in basic environments. Impressively, this hybrid material can achieve further enhanced OER catalytic performance with surface self-assembly through in-situ electrochemical oxidation activation in both gentle alkaline (GA: 1.0 M KOH at 298 K) and industrial alkaline (IA: 30 wt.% KOH at 353 K) water electrolysis conditions. The transition processes are revealed in detail regarding the chemical, structural, and catalytic properties of the catalysts served in the GA and IA conditions. The pristine quasi-amorphous Co-Fe-S is found to partially transform into crystallized Co(Fe)OOH in the GA condition, while it remains amorphous nature in the IA condition. The enhanced OER activity is attributed to the formation of active Co(Fe)OOH species with massively proliferated specific surface area, optimized electronic structure, and accelerated kinetics. The activated Co-Fe-S NFs@MS/NF exhibits excellent OER activity, achieving 10 and 500 mA cm−2 at ultralow potentials of 1.453 (iR corrected) and 1.517 V with outstanding durability in the GA and IA conditions, respectively. For full water splitting, the assembled two-electrode system based on the Co-Fe-S NFs@MS/NF anode and a Co-S based cathode affords voltages of only 1.518 and 1.685 V to robustly deliver 10 and 500 mA cm−2 in GA and IA conditions over 200 h, respectively.

Comparative Study of PtNi Nanowire Array Electrodes toward Oxygen Reduction Reaction by Half-Cell Measurement and PEMFC Test.

A clear understanding of catalytic activity enhancement mechanisms in fuel cell operation is necessary for a full degree translation of the latest generation of non-Pt/C fuel cell electrocatalysts into high-performance electrodes in proton-exchange membrane fuel cells (PEMFCs). In this work, PtNi nanowire (NW) array gas diffusion electrodes (GDEs) are fabricated from Pt NW arrays with Ni impregnation. A 2.84-fold improvement in the oxygen reduction reaction catalytic activity is observed for the PtNi NW array GDE (cf. the Pt NW array GDE) using half-cell GDE measurement in a 0.1 M HClO4 aqueous electrolyte at 25 °C, in comparison to only a 1.07-fold power density recorded in the PEMFC single-cell test. An ionomer is shown to significantly increase the electrochemically active surface area of the GDEs, but the PtNi NW array GDE suffers from Ni ion contamination at a high temperature, contributing to decreased catalytic activities and limited improvement in operating PEMFCs.

A novel electrode with multifunction and regeneration for highly efficient and stable symmetrical solid oxide cell

Symmetrical solid oxide cells (SSOCs) have been extensively recognized due to their simple cell configuration, low cost and reliability. High performance electrode is the key determinant of SSOCs. Herein, a multifunctional perovskite oxide La0.6Ca0.4Fe0.8Ni0.2O3-δ (LCaFN) is investigated as electrode for SSOCs. The results confirm that LCaFN shows excellent oxygen reduction reaction (ORR), oxygen evolution reaction (OER), carbon dioxide reduction reaction (CO2-RR) and hydrogen oxidation reaction (HOR) catalytic activity. In SOFC mode, the SSOCs with LCaFN achieve good electrochemical performance with maximum power density of 300 mW cm−2 at 800 °C. For pure CO2 electrolysis in SOEC mode, polarization resistance of 0.055 Ω cm2 and current density of 1.5 A cm−2 are achieved at 2.0 V at 800 °C. Besides, the cell shows excellent stability both in SOFC mode and SOEC mode. Most importantly, SSOCs with symmetrical LCaFN electrodes show robust and regenerative performance under anodic or cathodic process during the switching gas, showing the great reliability of the SSOCs. The results show that this novel electrode offers a promising strategy for operation of SSOCs.

Abstract 2713: Elucidation of bone metastasis using a caudal artery injection mouse model and Akaluc-AkaLumine near-infrared bioluminescence technology

Abstract Bone is one of the most common sites of metastasis for various primary tumors including breast, prostate and lung cancers. We have addressed molecular basis underlying bone metastasis using newly developed murine model of bone metastasis and near-infrared bioluminescence technologies. Our new murine model overcomes several limitations in the current standard model by intra-cardiac (IC) injection of cancer cells [1]. We found that the caudal artery is a new pathway to predominantly deliver cancer cells to the bone marrow of hind limbs in mice. Intra-caudal arterial (CA) injection is technically as easy as tail vein injection [2]. In addition, CA injection delivered cancer cells >10-fold more efficiently than IC injection. This accelerated the development of bone metastasis in hind limbs with wide variety of cell lines. We have combined the CA injection model with near-infrared bioluminescence imaging. Bioluminescence imaging (BLI) with firefly luciferases and its natural substrate D-luciferin has been indispensable to noninvasively monitor metastasis development in mice. To improve deep-tissue imaging, synthetic luciferin AkaLumine has successfully extended the wavelength of firefly bioluminescence to the near-infrared region where tissue is more transparent to light [3]. More recently, our collaborators created an engineered luciferase Akaluc that displays high catalytic activity in reaction with AkaLumine [4]. AkaLumine-Akaluc bioluminescence imaging (AkaBLI) is capable of noninvasive visualization of single cancer cells deep inside mice. Combining the CA injection model with AkaBLI technology is a powerful tool for elucidating the mechanism of bone metastasis in small animals.

Stable and Catalytically Active Shape-Engineered Cerium Oxide Nanorods by Controlled Doping of Aluminum Cations.

Shape-engineered nanocrystals (SENs) promise a better selectivity and a higher activity in catalytic reactions than the corresponding non-shape-engineered ones because of their larger specific surface areas and desirable crystal facets. However, often, it is challenging to apply SENs in practical catalytic applications at high reaction temperatures, where SENs deforms into more stable, less active nanoparticles. In this paper, we show that atomic layer deposition (ALD) of Al2O3 at 200 °C can controllably dope Al cations into the shape-engineered CeO2 nanorods (NRs) to not only increase their shape transition temperature from 400 °C to beyond 700 °C but also greatly increase their specific reversible oxygen storage capacity (srOSC). The substituted Al3+ ions impede the surface diffusion of Ce ions and therefore improve the thermal stability of CeO2 NRs. These Al3+ dopants form -Al-O-Ce-O- clusters, which are new Ce species and can be reversibly reduced and oxidized at 500-700 °C. This low-temperature chemical doping method decouples the synthesis process of SENs from the doping process and maintains the shape of the SENs during the activation of dopants. This concept could be adopted to enable the applications of other SENs in challenging high-temperature environments.

Cathodic activation of synthesized highly defective monoclinic hydroxyl‐functionalized ZrO 2 nanoparticles for efficient electrochemical production of hydrogen in alkaline media

The high electrochemical stability of Zirconia (ZrO2) at high potentials strongly suggested it as an alternative to carbon supports, which experience reduced efficiency due to some corrosion problems particularly during prolonged electrocatalysis activity. However, the use of ZrO2 was limited by its low electrical conductivity and surface area. In this work, we developed a methodology for synthesizing monoclinic ZrO2 NPs with increased surface area and improved electrical/electrocatalytic characteristics without using any carbon-based co-support material or any metallic nanoparticles. In this context, for the first time, highly defective hydroxyl-functionalized ZrO2 NPs (designated here as ZT NPs) were prepared by a hydrothermal route in the presence of sodium tartrate as a mineralizer. XRD analysis demonstrated that the produced zirconia was semicrystalline microspheres, consisting of monoclinic ZrO2 NPs with high lattice defects. The addition of tartrate ions decreased the crystallite size and increased the defects and microstrain. At the same time, the alkaline hydrogen evolution reaction (HER) catalytic activity of ZrO2 NPs was significantly increased when using sodium tartrate as mineralizer; the overpotential required to obtain 10 mA cm−2 (η10) dropped down from 490 to merely 235 mV, while an exchange current density (jo) increased 12 times to 0.22 mA cm−2. The presence of structural defects (revealed by XRD) and the increased number of active surface sites contending O-H groups (evidenced from ATR-FTIR and XPS) as well as the enhanced electrochemical active surface area (confirmed from double-layer capacitance measurements) were the main reasons behind the high catalytic performance. The ZrO2 NPs catalytic activity increased even further during the long-term stability tests under severe cathodic conditions (ZT*, ZrO2 NPs obtained after the long-term stability, has jo = 0.47 mA cm−2 and η10 = 140 mV), approaching the activity of Pt/C catalyst. This process was assisted by mineralizer removal from the catalyst (testified by XPS). Our studies revealed that ZT* are characterized by larger electroactive surface area and more structure defects compared to ZT, where surface area and microstrains resulting from surface hydroxylation open cavities in zirconia structure.

Synthesis of Ultrathin MoS2 Nanosheets Embedded in 3D Hierarchically Nitrogen‐and‐Sulfur Co‐Doped Porous Carbon Composites as Efficient Oxygen Reduction Reaction Catalyst

AbstractCatalysts comprising MoS2 incorporated into 3D hierarchically N,S co‐doped carbon composites (MoS2@NSC) were prepared through a facile and scalable method by using the functional fluidic acrylonitrile telomer as a carbon source and doping agent, and SiO2 as a hard template. The optimal catalyst, MoS2@NSC‐2, showed effective oxygen reduction reaction (ORR) catalytic activity with the initial potential of 0.93 V and half‐potential of 0.82 V in basic electrolyte. In addition, MoS2@NSC‐2 favored a four‐electron reduction process and demonstrated a superior durability and methanol tolerance, which could be ascribed to its unique porous structure that can effectively facilitate the transfer of electrolyte and O2 molecules. The Mo−Nx species are formed due to the doping of N atoms into the crystal lattice of MoS2, which can further enhance the ORR catalytic activity. Our work affords a forward‐looking strategy for designing efficient and low‐cost ORR catalysts on a large scale.

Poly-active centric Co3O4-CeO2/Co-N-C composites as superior oxygen reduction catalysts for Zn-air batteries

Zinc-air battery is one of the most promising next-generation energy conversion and storage systems. Green and low-cost catalysts with high oxygen reduction reaction (ORR) catalytic activity are desired to meet the requirements of Zinc-air batteries. Herein, poly-active centric Co3O4-CeO2/Co-N-C (ketjenblack carbon) catalysts were prepared by a facile method. The Co3O4 and CeO2 nanoparticles are uniformly anchored on the surface of Co and N doped carbon support. The half-wave potential of Co3O4-CeO2/Co-N-C in the rotating disk electrode testing is close to that of Pt/C. The Zn-air battery using Co3O4-CeO2/Co-N-C as the cathode catalyst can provide a high specific capacity of 728 mA h g−1 at 20 mA cm−2 and maintain a stable discharge voltage. The remarkable catalytic performance is mainly attributed to the synergistic effect among Co3O4, CeO2 and Co-N-C, the outstanding electrical conductivity and the large surface area. Benefitting from the high catalytic activity, environmental friendliness and the facile synthesis process, Co3O4-CeO2/Co-N-C catalyst lends itself well to a great prospect in the application of metal-air batteries.

2D iron-doped nickel MOF nanosheets grown on nickel foam for highly efficient oxygen evolution reaction

Recently, metal–organic framework (MOF) manifests an outstanding oxygen evolution reaction (OER) catalytic activity due to its structural diversity, highly ordered pore structure and abundant active sites. Herein, through a facile one-step solvothermal method, iron-doped nickel MOF nanosheets in situ grown on conductive nickel foam (Fe-Ni MOF NSs/NF) were conveniently fabricated as efficient OER catalyst, using only one kind of metal salt precursor. The ultrathin 2-dimensional sheet structure possesses highly exposed surface area and numerous metal sites which are beneficial to electrocatalytic OER performance. The Fe-Ni MOF NSs/NF presents superior OER activity in 1 M KOH, requiring overpotentials of 258 and 270 mV to deliver the current density of 50 and 100 mA cm−2, along with a low Tafel slope of 40.8 mV dec−1. Moreover, the durability of the Fe-Ni MOF NSs/NF catalyst is also outstanding, exhibiting only minor chronoamperometric decay after 24 h continuous operation at 50 mA cm−2. The excellent OER activity could be ascribed to the coupling effects of ultrathin-nanosheet structure, favorable charge transfer kinetics, high conductivity and excellent intrinsic catalytic activity. This facile and economical strategy might be advantageous to prepare other high-performance MOF-based OER catalysts.

Thermal conversion of hollow nickel-organic framework into bimetallic FeNi3 alloy embedded in carbon materials as efficient oer electrocatalyst

Rapid deployment of renewable energy causes a significant change in environmental benefits. Thus, the transition metal-based electrocatalysts are developed to achieve efficient water splitting. Here a simple three-step method is adopted to successfully synthesize a type of hollow MOF-derived three-dimensional carbonaceous matrix that is randomly loaded with numerous FeNi3 alloy nanoparticles (NiFeC). In this work, the as-obtained NiFeC-800–5(carbonization temperature: 800 °C; pyrolysis rate: 5 °C/min) shows an excellent oxygen evolution reaction catalytic activity in 1.0 M KOH electrolyte, with a low overpotential of 269 mV at 10 mA cm-2 and a low Tafel slope of 72 mV dec‑1. Moreover, it exhibits an ultrastable durability after being electrolyzed continuously for 10 h, which is originated from these fine alloys encapsulated into the hierarchically porous carbonaceous material. Finally, we have proposed morphological and chemical changes for the NiFeC-800–5sample, in which the solid MOF precursor will be gradually etched into the hollow morphology by the strong hydrolysis of Fe(III) ions at high temperature, and the optimal carbonization temperature and heating rate are also well investigated. Moreover, the above approach can be used to obtain other MOF derived bimetallic alloy nanoparticles encapsulated into carbon materials for the energy conversion and storage applications.

Preparation and electrochemical performances of silver (alloy) nanoparticles decorated on reduced graphene oxide, using self-polymerization of dopamine in an acidic environment

Self-polymerization of dopamine, in either an alkaline or an acidic environment, to form polydopamine is a material-independent surface coating technique, influencing almost all areas of material science and engineering. We demonstrated a simple, two-step method to prepare in-situ silver or silver-copper alloy nanoparticles on the surface of reduced graphene oxides, using polydopamine formed in an acidic medium. The acidic medium was created by a nonthermal micro-hollow cathode discharge device and the device was operated at atmospheric pressure, using air as the working gas. The nanocomposites were characterized with SEM, EDX, ICP-OES, and FT-IR; the electrochemical catalytic activity was tested using rotating disk electrode. The characterization methods confirmed the formation of the nanocomposites, which contain polydopamine, reduced graphene oxides, and metal nanoparticles or nanoalloy. We hypothesized that by alloying silver and copper on the surface of reduced graphene oxides, the oxygen reduction reaction (ORR) catalytic activity of the nanocomposites will be enhanced through both alloying and substrate effects. The size range of the nanoparticles is between 10 nm and 15 nm. We find that both the silver and alloy samples catalyze the ORR via a four-electron mechanism. The alloy nanocomposites showed better performance indicator parameters than the silver one, in both mass activity and kinetic current density. This preparation method has paved a new way of synthesizing an ORR catalyst in an environmentally friendly manner.

The surface structure of β-NiOOH (001) under reaction conditions and its effect on OER activity: An ab initio study

β-NiOOH shows excellent oxygen evolution reaction (OER) catalytic activity under alkaline conditions, but the surface structure under the working environment is not yet fully established. Through ab initio thermodynamic approach, the relationship between catalyst surface structure and pH, electrode potential was studied. For the most stable state of the catalyst surfaces, three adsorbing oxygen atoms and one Ni vacancy form. Doped iron decreases the formation energy of Ni vacancy thus increasing the stable range of surface states. OER mechanism was explored based on the obtained most stable structures. The first step of the reaction is the desorption of oxygen rather than the formation of *OH due to large Steric effects. Ni vacancy reduces the dehydrogenation energy of the adsorbate *OOH and the formation energy of oxygen radical. The interaction between iron and oxygen atom is large than the Ni and oxygen. Therefore, Fe-doped system reduces the formation energy of *O and changes the potential-limited step from the formation of adsorbate *O to the desorption of O2.