Number Of Catalytic Active Sites Research Articles

Comparative electrocatalytic behavior of mesoporous FeP and FeS2 for the hydrogen evolution reaction

FeP nanoparticles and FeS2 nanospheres with mesoporous surface are synthesized, and their performance is compared for the hydrogen evolution reaction under identical electrochemical conditions. The activity-determining characteristics of the electrodes, such as specific and electrochemically active surface area, electrochemical impedance and charge transfer resistance, Tafel slopes, number of catalytic active sites, and turnover frequency (TOF) are studied and correlated to their activity. Because of its larger surface area and reduced charge transfer resistance, the FeS2 showed superior HER performance than the FeP, despite the latter’s higher intrinsic catalytic activity. The electrocatalytic stability of the electrocatalysts are also compared.

Boosting Interfacial Electron Transfer and CO2 Enrichment on ZIF-8/ZnTe for Selective Photoelectrochemical Reduction of CO2 to CO.

Artificial photosynthesis is an effective way of converting CO2 into fuel and high value-added chemicals. However, the sluggish interfacial electron transfer and adsorption of CO2 at the catalyst surface strongly hamper the activity and selectivity of CO2 reduction. Here, we report a photocathode attaching zeolitic imidazolate framework-8 (ZIF-8) onto a ZnTe surface to mimic an aquatic leaf featuring stoma and chlorophyll for efficient photoelectrochemical conversion of CO2 into CO. ZIF-8 possessing high CO2 adsorption capacity and diffusivity has been selected to enrich CO2 into nanocages and provide a large number of catalytic active sites. ZnTe with high light-absorption capacity serves as a light-absorbing layer. CO2 molecules are collected in large nanocages of ZIF-8 and delivered to the ZnTe surface. As evidenced by scanning electrochemical microscopy, the interface can effectively boost interfacial electron transfer kinetics. The ZIF-8/ZnTe photocathode with unsaturated Zn-Nx sites exhibits a high Faradaic efficiency for CO production of 92.9% and a large photocurrent of 6.67 mA·cm-2 at -2.48 V (vs Fc/Fc+) in a nonaqueous electrolyte at AM 1.5G solar irradiation (100 mW·cm-2).

Surface decoration of plasmonic Ag nanospheres for enhanced visible light photocatalysis of BiVO4

The industrial concern of producing benzaldehyde (BD) more efficiently is the key aspect of this work. Therefore, the oxidation of benzyl alcohol (BA) by photocatalytic route was chosen. The amoeba-like BiVO4 (BV) particles were synthesized by co-precipitate method since it gives higher yield when compared to other methods and silver nanoparticles were decorated over its surface by photo deposition method. Due to surface plasmon resonance (SPR effect), the decorated samples showed enhanced optoelectronic properties. The band edge positions shifted to higher energy levels profitably paving the way for the production of superoxide radicals (•O2−) effectively. The optimal catalyst material was engineered in such a way that it would facilitate the production of both •O2− and BA* radicals and inhibits the production of BD* radical. The decorated silver nanoparticles aided in increasing the surface area and the number of catalytic active sites, therein a 4.7-fold increase in benzaldehyde yield was achieved when compared to pure BV. Since monoclinic BV possesses piezoelectric property, the use of ultrasound in the reaction medium boosted the efficiency of the reaction and henceforth a maximum conversion of 88.29 % was obtained. Hydrogen peroxide formed as a byproduct, adds commercial value to this reaction.

Enhanced electrochemical performance of MoSe2 nanosheets on CoAl- layered double hydroxide for oxygen evolution reaction

The design of high-efficiency electrocatalysts for water electrolysis has attracted much attention. A crucial half-reaction in electrochemical water splitting is the oxygen evolution reaction (OER), which suffers from sluggish reaction kinetics due to the high-energy barrier of the complex electron transfer process. This study presents a MoSe2@CoAl-layered double hydroxide (LDH) hybrid nanostructure prepared using the facile hydrothermal method and investigated as a potential OER electrocatalyst. Morphological analysis indicated that the MoSe2 formed in very thin nanosheet structures containing multiple defects on the LDH platelets, increasing the number of catalytic active sites. Compared with pristine MoSe2 and CoAl-LDH, the obtained MoSe2@CoAl-LDH catalyst exhibited enhanced electrocatalytic activity for the OER in an alkaline solution. The MoSe2@CoAl-LDH electrocatalyst showed an overpotential of 360 mV at a current density of 10 mA cm−2 and a small Tafel slope of 53 mV dec−1. In addition, it demonstrated good electrochemical stability. The MoSe2@CoAl-LDH exhibited a lower Tafel slope than commercial RuO2, indicating faster electron transfer on the MoSe2@CoAl-LDH electrode.

CuAs2O4: Design, Hydrothermal Synthesis, Crystal Structure, Photocatalytic Dye Degradation, Hydrogen Evolution Reaction, Knoevenagel Condensation Reaction, and Thermal Studies.

CuAs2O4 has been explored as a heterogeneous catalyst in the fields of photocatalysis, electrocatalysis, and solvent-free organic transformation reactions. The homogeneity has been successfully attained for the first time by designing a pH-assisted hydrothermal synthesis technique. Single-crystal X-ray diffraction studies reveal that no phase transition has been observed by lowering the temperature up to 103 K with no existence of satellite reflections. The crystal structure exhibits tetragonal symmetry with space group P42/mbc and consists of [CuO6] octahedra and [AsO3E] tetrahedra (E represents the stereochemically active lone pair). Structural investigation shows a cylindrical void inside the structure, which could lead to interesting physical and chemical properties. The photocatalytic dye degradation efficiency with methylene blue (MB) showed ∼100% degradation, though the degradation efficiency increased by 2-fold with the addition of 6% H2O2. The reusability of the catalyst up to the 10th cycle with ∼35% MB dye degradation has been established. It can exhibit HER activity with a low overpotential of 165 mV with respect to RHE to attain the current density of j = 10 mA cm-2. SEM and TEM revealed rod-shaped particles, which supported the large number of catalytic active sites. The structural consistency of the catalyst after photodegradation and HER studies is confirmed by the PXRD pattern. XPS confirms the oxidation state of Cu and As in the compound. The catalytic activity toward the Knoevenagel condensation reaction at moderate temperature under solvent-free condition is also studied. TG-DTA shows an endothermic minimum (Tmin) at 436 °C due to the mass loss of As2O3.

A cauliflower-like Ni metal-organic phosphate modified carbon paste electrode as an efficient catalyst for electrochemical water oxidation in neutral media

We fabricated the cauliflower-like Ni metal-organic phosphates (Ni-MOPh) with different synthesis time (Ni-MOPh-Ts, Ts = Times) as a carbon paste electrode material (Ni-MOPh-Ts/C) for oxygen evolution reaction (OER) in neutral media. The as-synthesized Ni-MOPh-12 h/C shows a better OER ability than that of Ni-MOPh-6 h/C and Ni-MOPh-2 h/C, which also shows conspicuous performance with the overpotential of 420 mV to obtain 10 mA cm−2. Reaction kinetics studies exhibit that Ni-MOPh-12 h/C can provide higher electrochemical ability, mainly due to the small charge transfer resistance, and a high number of catalytic active sites.

Design and Realization of Ni Clusters in MoS2@Ni/RGO Catalysts for Alkaline Efficient Hydrogen Evolution Reaction.

Due to their almost zero relative hydrogen atom adsorption-free energy, MoS2-based materials have received substantial study. However, their poor electronic conductivity and limited number of catalytic active sites hinder their widespread use in hydrogen evolution reactions. On the other hand, metal clusters offer numerous active sites. In this study, by loading Ni metal clusters on MoS2 and combining them with the better electrical conductivity of graphene, the overpotential of the hydrogen evolution reaction was reduced from 165 mV to 92 mV at 10 mA·cm-2. This demonstrates that a successful method for effectively designing water decomposition is the use of synergistic interactions resulting from interfacial electron transfer between MoS2 and Ni metal clusters.

Co@Co Cages Engineered from Hollowing MOFs for Enhanced Hydrogen Evolution Reaction Performance.

Advances in hollow engineering of metal-organic frameworks (MOFs) have enabled a variety of applications in catalysts, sensors, and batteries, but the hollow derivatives are often limited to hydroxides, oxides, selenides, and sulfides with the presence of additional elements from the environment. Here we have successfully synthesized hollow metallic Co@Co cages through a facile two-step strategy. Interestingly, the Co@Co(C) cages with a small amount of residual carbon show excellent catalytic performance due to the abundant exposed active sites and fast charge transfer. During the hydrogen evolution reaction, the overpotential of Co@Co(C) is as low as ∼54 mV at the current density of 10 mA cm-2, which is close to that of ∼38 mV for the Pt/C electrodes. The two-step synthesis strategy opens up opportunities for increasing the number of catalytic active sites and rates of charge/mass transfer while pushing the limits of materials utilization beyond that achieved in existing MOF-based nanostructures.

Carbon Nanofibers Coated with MOF-Derived Carbon Nanostructures for Vanadium Redox Flow Batteries with Enhanced Electrochemical Activity and Power Density

A unique synthetic approach has been introduced where nanostructurally grown zinc layered double hydroxide on graphitic carbon felt (CF) is converted into a zeolitic imidazolate framework (ZIF-8), and then, subsequent carbonization resulted in a N/O-functionalized porous carbon electrode (N,O/CF). Because of the presence of N/O-containing functional groups and deposition of ZIF-8-derived nanoporous carbon on the CF, the N,O/CF is found to be highly hydrophilic in nature with a large surface area. Cyclic voltammetry measurements with N,O/CF suggest the fast electrochemical kinetics of V(IV) ↔ V(V) reactions. Polarization curves and electrochemical impedance spectroscopy measurements of the vanadium redox flow battery (VRFB) assembly illustrate the significant decrease in charge transfer resistance at electrode surfaces. At 50 mL/min electrolyte flow rate, N,O/CF delivers energy efficiencies of 83.11 and 76.66% at current densities of 40 and 80 mA/cm2, respectively. The values are 82.59 and 76.39%, respectively, at 100 mL/min, showing the negligible effect of the flow rate. The power density of VRFBs at various electrolyte flow rates is also presented, which increases with increasing flow rates and is higher for N,O/CF (∼821 mW/cm2) than for bare CF (606 mW/cm2). The stability test confirms the retention of energy, voltage, and coulombic efficiencies after recycling of the electrode. The above-mentioned findings of improved performance of VRFBs with employing the N,O/CF electrode are a cumulative effect of enhanced nanoporosity, an increased number of catalytic active sites, high wettability, and low charge transfer resistance.

Tube-Sponge-Inspired Hierarchical Electrocatalysts with Boosted Mass and Electron Transfer for Efficient Oxygen Evolution.

Hindered gas bubble release and limited electron conducting process represent the major bottlenecks for large-scale electrochemical water splitting. Both the desorption of bubbles and continuous electron transport are achievable on the surfaces of biomimetic catalytic materials by designing multiscale structural hierarchy. Inspired by the tubular structures of the deep-seasponges, an exceptionally active and binder-free porous nickel tube arrays (PNTA) decorated with NiFe-Zn2+ -pore nanosheets (NiFe-PZn ) are fabricated. The PNTA facilitate removal of bubbles and electron transfer in the oxygen evolution reaction by reproducing trunks of the sponges, and simultaneously, the NiFe-PZn increase the number of catalytic active sites by simulating the sponge epidermis. With improved external mass transfer and interior electron transfer, the hierarchical NiFe-PZn @PNTA electrode exhibits superior oxygen evolution reaction performance with an overpotential of 172mV at 10mAcm-2 (with a Tafel slope of 50mVdec-1 ). Furthermore, this electrocatalytic system recorded excellent reaction stability over 360h with a constant current density of 100mAcm-2 at the potential of 1.52V (versus RHE). This work provides a new strategy of designing hierarchical electrocatalysts for highly efficient water splitting.

P-induced Co-based interfacial catalysis on Ni foam for hydrogen generation from ammonia borane

Co-based monolithic phosphides have caught attention due to their stability and corrosion resistance properties during the catalytic reaction. Herein, P-induced Co-based interfacial phosphides Co-CoP-NC/NF are prepared through the PH3-phosphorization. The theoretical and experimental analysis confirms the uniform growth of Co-CoP nanoparticles (NPs) with turmeric-like morphology. Co-CoP NPs (average size = 8.78 nm) express prominent interfacial interaction and a strong electronic interaction between metal sites and doped phosphorous (P). Thus, P inducing synergistically increases the number of catalytic active sites (CoP) and electronic modulation of metallic sites (Co). The optimized catalyst Co-CoP-NC/NF-2 express the excellent and the best-ranked catalytic activity for ammonia borane hydrolysis with hydrogen evolution rate (rB = 2500 mL min−1 g−1Co), turnover frequency (TOF = 600 h−1), and apparent activation energy (Ea = 30.6 kJ mol−1). This work provides a potential avenue for developing monolithic catalysts for industrial applications in the field of heterogeneous catalysis and sustainable energy.

Cyclophosphazene Intrinsically Derived Heteroatom (S, N, P, O)-Doped Carbon Nanoplates for Ultrasensitive Monitoring of Dopamine from Chicken Samples

A novel, metal-free electrode based on heteroatom (S, N, P, O)-doped carbon nanoplates (SNPO-CPL) modifying lead pencil graphite (LPG) has been synthesized by carbonizing a unique heteroatom (S, N, P, O)-containing novel polymer, poly(cyclcotriphosphazene-co-2,5-dioxy-1,4-dithiane) (PCD), for precise screening of dopamine (DA). The designed electrode, SNPO-CPL-800, with optimized percentage of S, N, P, O doping through the sp2-carbon chain, and a large number of surface defects (thus leading to a maximum exposition number of catalytic active sites) led to fast molecular diffusion through the micro-porous structure and facilitated strong binding interaction with the targeted molecules in the interactive signaling transducer at the electrode-electrolyte interface. The designed SNPO-CPL-800 electrode exhibited a sensitive and selective response towards DA monitoring, with a limit of detection (LOD) of 0.01 nM. We also monitored DA levels in commercially available chicken samples using the SNPO-CPL-800 electrode even in the presence of interfering species, thus proving the effectiveness of the designed electrode for the precise monitoring of DA in real samples. This research shows there is a strong potential for opening new windows for ultrasensitive DA monitoring with metal-free electrodes.

Green synthesis of Ag ultra-fine nano-catalyst supported on layered double oxide and chitosan: Accelerated reduction of 4-nitrophenol to 4-aminophenol

In this research, the green synthesis of a silver nanoparticle (Ag NPs) based nano-catalyst for reducing 4-nitrophenol (4-NP) pollutants were explained. Hence, instead of using chemical reductant, natural extract of green tea was utilized as reducing agent to prepare Ag NPs. The obtained Ag NPs had uniform size and shape. The small size of Ag NPs helps exited electron to be stabilized and extends lifespan during a reduction reaction. Then, layered double hydroxides (LDHs) was prepared, and after calcination was added to Ag NPs. The calcination of LDH leads to a significant increase in the number of catalytic active sites, thereby enhancing catalyst function. Besides, chitosan (CS) was chosen as a natural polymer matrix. Ag-LDH hybrids can remain immobilized and well-dispersed on CS matrix. The CS matrix also facilitates the separation process. More importantly, it enhances reusability of the nano-catalyst noticeably and accordingly plays an important role in the synthesis of the reusable high-performance nano-catalyst. Finally, the prepared CS/Ag-LDH NC film reduced 4-NP to 4–aminophenol in 5 min with a conversion percentage of 99.01% ± 0.13. The effect of various parameters like pH, catalyst amount, NaBH4 concentration, and 4-NP concentration was evaluated. Based on the obtained findings, reaction kinetics is pseudo-first-order with an apparent rate constant of 1.65 × 10−2 (s−1), and the activation energy was calculated to be 13.93 kJ mol−1. Presence of CS enhanced reusability of the nano-catalyst noticeably so that, performance of the nano-catalyst remained unchanged after five reuse cycles.

Enhanced hydrogen evolution performance by nanoarchitectonics of Fe/Co alloy electrode beyond Fe/Co/Ni alloy electrode

With the increasing global energy demand, hydrogen production from electrolytic water became the main way to prepare efficient and clean hydrogen energy. Transition metal catalyst were promising hydrogen evolution catalyst for low cost, stable performance and high catalytic activity. In this study, Fe–Co–Ni, Co–Fe, Ni–Fe and Co–Ni alloy electrodes were prepared by electrodeposition. Among the four alloys, Co–Fe showed the best hydrogen evolution performance. The surface of Co–Fe alloy electrode coating was composed of round small particles of different sizes closely combined to form a large complex. In the alloy, Co was accounted for 62.2% and Fe was accounted for 37.8%. The increase of Co content increased the specific surface area of the electrode, provided a large number of catalytic active sites, and improved the hydrogen evolution performance. In the Co–Fe alloy electrode, Fe was existed in the form of Fe2+ and Fe3+, Co was existed in the form of Co2+. The electrochemical test results showed that Co–Fe alloy electrode had the highest electrocatalytic activity. Since the conductivity of cobalt hydroxide and iron hydroxide generated in the strong alkali environment, which was stronger than that of nickel hydroxide, the internal resistance of the Co–Fe alloy electrode in the hydrogen evolution process was reduced. Under the same conditions, the Co–Fe alloy electrode needed only 1483 mV overpotential to drive a current density of 0.1 A/cm2. The Tafel slope of Co–Fe alloy electrode was the smallest, only 144.04 mV/dec, and the electron transmission efficiency was the highest. Co–Fe alloy electrode had the lower electron conduction resistance and better electrochemical hydrogen evolution performance.

Latest Advances in Metasurfaces for SERS and SEIRA Sensors as Well as Photocatalysis.

Metasurfaces can enable the confinement of electromagnetic fields on huge surfaces and zones, and they can thus be applied to biochemical sensing by using surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA). Indeed, these metasurfaces have been examined for SERS and SEIRA sensing thanks to the presence of a wide density of hotspots and confined optical modes within their structures. Moreover, some metasurfaces allow an accurate enhancement of the excitation and emission processes for the SERS effect by supporting resonances at frequencies of these processes. Finally, the metasurfaces allow the enhancement of the absorption capacity of the solar light and the generation of a great number of catalytic active sites in order to more quickly produce the surface reactions. Here, we outline the latest advances in metasurfaces for SERS and SEIRA sensors as well as photocatalysis.

Nanocatalyst-Assisted Facile One-Pot Synthesis of Glycidol from Glycerol and Dimethyl Carbonate.

This paper reports the facile one-pot synthesis of glycidol via the transesterification of glycerol with dimethyl carbonate using KNO3/Al2O3 nanoparticles as supporting catalysts. KNO3/Al2O3 nanoparticles were prepared by the impregnation method. XRD and FT-IR analyses indicated an interaction between KNO3 and Al2O3 that enabled the decomposition of KNO3 during the process and resulted in the formation of KAl5O8, the Al–O–K group, and K2O. K2O was recognized as one of the active sites of the catalyst. SEM results indicated the high performance of the supporting catalyst, as the catalytic activity depended on both the number of catalytic active sites and their distribution. The yield of glycidol was 64% at the expense of 95% glycerol under moderate reaction conditions (120 min, 1 atm, and 70 °C). The nanocatalyst prepared at 800 °C with a loading amount of 30% KNO3 was the most efficient for the synthesis of glycidol. Furthermore, the catalyst was recovered and reused without a loss of efficiency even after the fourth recycling. A plausible mechanism for the one-pot synthesis of glycidol has also been proposed.

Co-Doped Zeolite-GO Nanocomposite as a High-Performance ORR Catalyst for Sustainable Bioelectricity Generation in Air-Cathode Single-Chambered Microbial Fuel Cells.

High-performance cobalt (Co) nanoparticles supported on a zeolite-graphene oxide (1:2) matrix (catalyst Z2) are synthesized through a facile reduction method. In multipoint Brunauer-Emmett-Teller (MBET) surface area analysis, catalyst Z2 demonstrates a higher surface area compared with other synthesized catalysts, indicating the presence of a larger number of catalytic active sites, and supports outstanding ORR performance due to an improved electron-transfer rate and a higher number of redox-active sites. Furthermore, it is observed that catalyst Z2 is an excellent electrocatalytic material due to its low charge-transfer resistance and higher oxygen reduction reaction (ORR) activity. Herein, the electrocatalytic investigation suggests that catalyst Z2 at a potential of 483 mV and a reduction current of -0.382 mA displays a higher electrocatalytic performance and higher stability toward ORR compared with other synthesized catalysts and even the standard Pt/C catalyst. Also, when catalyst Z2 is applied as an air-cathode ORR electrocatalyst for a single-chambered microbial fuel cell (SC-MFC), the SC-MFC coated with catalyst Z2 generates the maximum power density of 416.78 mW/m2, which is 306% higher than that of SC-MFC coated with Pt/C (102.67 mW/m2). In fact, the longer stability and electronic conductivity have contributed to an outstanding ORR activity of the nanocomposite due to its porous surface morphology and the presence of the functional groups in the zeolite-GO support matrix. In brief, Co (cobalt) nanoparticles doped on a zeolite-GO (1:2) support matrix are promising cathode electrocatalysts in the practical application of MFCs and other related devices.

The study of amorphous La@Mg catalyst for high efficiency hydrogen storage

Amorphous catalysts have a large number of catalytic active sites. Here, we report a magnesium composite trace lanthanum catalyst (La@Mg), in which La and Mg layers form amorphous Mg–La compound on the surface of layered Mg. The test shows this La@Mg has hydrogen storage capacity of about 7.6 wt% and hydrogen desorption of 7.2 wt%, higher than that of crystalline La@Mg and sole Mg, rapid absorption/desorption kinetic and stable reversible absorption/desorption cycles. La@Mg exhibits an optimistic hydrogen storage performance than Mg-based materials previously reported in the literature. Combined with theoretical calculations, it is shown that the amorphous Mg–La has an catalysis on hydrogen storage performance of La@Mg system, which contributing to the dispersion of Mg and providing channels for hydrogen diffusion, facilitating hydrogenation by accelerating H atoms diffuse between the subsurface and the surface. This work provides experiment and mechanism guidance for the development of efficient hydrogen storage materials.

Conversion of Interfacial Chemical Bonds for Inducing Efficient Photoelectrocatalytic Water Splitting.

Sp-C-hybridized alkyne bonds present the natural advantages of interacting with metal atoms and have the ability to generate a large number of new catalytic active sites on the surface and the interfaces, thus greatly promoting the efficient progress of various light/electrochemical reactions. In this work, we have successfully fabricated a novel type of interfacial structure containing sp-C-Mo/O bonds and mixed Mo valence states with outstanding catalytic activity and stability for photoelectrocatalytic (PEC) overall water splitting in a wide pH range (0-14), due to the presence of sp-carbon-rich graphdiyne. For example, in alkaline conditions (pH = 14), the overpotentials of oxygen and hydrogen evolution reactions at 10 mA cm-2 are 165 and 8 mV. When being used as an electrolyzer, the cell voltage of this catalyst is only 1.40 V to achieve 10 mA cm-2. The high PEC activity of graphdiyne@molybdenum oxide originates from the conversion of chemical bonds at the sp-C hybrid interface and the coexistence of multivalent states of molybdenum, triggering a large number of catalytic active sites, greatly promoting charge transfer and lowering water dissociation energy.

Formation/Decomposition of Li2O2 Induced by Porous NiCeOx Nanorod Catalysts in Aprotic Lithium-Oxygen Batteries.

To realize the utilization of high-performance lithium-oxygen batteries (LOBs), a rational-designed cathode structure and efficient catalytic materials are necessary. However, side products accumulated during battery cycling seriously affects the performance. Designing a cathode catalyst that could simultaneously facilitate the catalytic efficiency of the main reaction and inhibit the side reactions will make great sense. Herein, NiCeOx was proposed for the first time as a bifunctional cathode catalyst material for LOBs. The combined action of NiO and CeO2 components was expected to facilitate the decomposition of byproducts (e.g., Li2CO3), increase the oxygen vacancy content in CeO2, and enhance the adsorption of oxygen and superoxide. NiCeOx nanorods (NiCeOx PNR) were prepared using electrospinning method. It showed a hollow and porous nanorod (PNR)-like structure, which provided a large number of catalytic active sites and facilitated the transport of reactants and the deposition of discharge products. As a result, a high specific discharge capacity (2175.9 mAh g-1) and a long lifespan (67 cycles at 100 mA g-1 with a limited capacity of 500 mAh g-1) were obtained.