A strategy for easy synthesis of carbon supported Co@Pt core–shell configuration as highly active catalyst for oxygen reduction reaction

An oxygen-mediated galvanic battery reaction strategy has been developed to one-step synthesize carbon-supported Co@Pt core–shell nanostructures. Relying on this strategy, a structural evolution of 3-D Pt-on-Co bimetallic nanodendrites into Co@Pt core–shell configuration is readily achieved in our study. These well-supported and low-Pt-content nanostructures show superior electrocatalytic activities to oxygen reduction reaction. Especially, the supported Co@Pt core–shell electrocatalyst for oxygen reduction reaction shows a high activity with the maximal Pt-mass activity of 465 mA mg⁻¹ Pt at 0.9 V (vs. RHE). The present investigation clearly demonstrates that the design and synthesis of the core–shell nanostructures is a viable route for building Pt-based electrocatalysts with optimized utilization efficiency and higher cost performance.     

TiO2–CdS supported CuNi nanoparticles as a highly efficient catalyst for hydrolysis of ammonia borane under visible-light irradiation

TiO₂–CdS nanotubes (NTs) were used for the first time as a support to load metal nanoparticles (NPs) for the hydrolysis of ammonia borane (AB) which is a new strategy. The TiO₂–CdS NTs support was first synthesized using a hydrothermal method, and then the CuNi NPs were loaded using a liquid-phase reduction method. The synthesized samples were characterized by XRD, SEM-EDS, TEM, XPS, ICP, UV–Vis, and PL analyses. The characterization results show that the CuNi NPs existed in the form of an alloy with a size of ~1.2 nm and uniformly dispersed on the support. Compared with their single metal counterparts, the bimetallic CuNi-supported catalysts showed a higher catalytic activity in the hydrolysis of AB under visible-light irradiation: Cu_0·45Ni_0·55/TiO₂–CdS catalyst had the fastest hydrogen evolution rate with a high conversion frequency (TOF) of 25.9 mol_H2·mol_cat⁻¹ min⁻¹ at 25 °C and low activation energy of 32.8 kJ mol⁻¹. Cu_0.45Ni_0.55/TiO₂–CdS catalyst showed good recycle performance, maintaining 99.3% and 85.6% of the original hydrogen evolution rate even after five and ten recycles, respectively. Strong absorption of visible light, improved electron–hole separation efficiency, and metal synergy between Cu and Ni elements played a crucial role in improving the catalytic hydrolysis performance of AB. The catalyst prepared in this study provides a new strategy for the application of photocatalysts.     

Electrochemical performance of Pd and Au–Pd core–shell nanoparticles on surface tailored carbon black as catalyst support

The present work studies the influence of the surface chemistry of carbon supports on the electrochemical behaviour of Pd and Au–Pd core–shell (CS) nanoparticles. Vulcan XC-72R was chemically modified by different acid treatments, inducing changes in the volume of the mesopores and surface density of oxygenated species. The CS nanostructures featuring 19 nm Au cores and 10 nm Pd shells were synthesized by colloidal methods and subsequently incorporated to the carbons supports. Pd nanoparticles were prepared by impregnating a Pd precursor into the modified carbons followed by reduction with sodium borohydride. The use of different preparation methods allowed the independent study of the effect of the support on the morphology/distribution of the nanoparticles and on the reactivity of the nanoparticles, through their interaction with organic molecules. The electrocatalysts were characterised by XRD, EDX, Raman spectroscopy and contact angle measurements. CO and formic acid (HCOOH) electro-oxidation were studied using cyclic voltammetry and chronoamperometry. The effect of the carbon support on the electrocatalytic activity was highly dependent on the method of preparation. Pd nanoparticles obtained by impregnation showed higher HCOOH oxidation currents when supported on the highly oxidised Vulcan support. This is due to the generation of smaller particle sizes (2.3 nm) as a result of the high density of oxygenated functional groups. On the other hand, the CS nanostructures are significantly less active in highly oxidised Vulcan as a results of specific chemical interactions which may be related to the formation of oxides. The implication of these findings towards rationalising particle–substrate interactions are briefly discussed.     

Bimetallic palladium–iridium alloy nanoparticles as highly efficient and stable catalyst for the hydrogen evolution reaction

Addressed herein, a highly efficient, durable and uniformly dispersed activated carbon supported palladium–iridium nanomaterials (3.42 ± 0.34 nm) were reported for the first time as a catalyst in dimethylamine-borane dehydrogenation reaction at the room temperature. The activated carbon supported palladium-iridium nanosheet (Pd–Ir NPs) is obtained by a simple ultrasonic reduction method, and the fabricated nanocatalyst have been defined by Ultra-Violet-Visible (UV–VIS), Raman spectroscopy, X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HR-TEM). These newly prepared Pd–Ir nanocomposites were found to be highly efficient and stable for dehydrocoupling of dimethylamine borane. The catalytic activity of the Pd–Ir NPs was excellent by showing the one of the best catalytic activity with a very high turnover frequency (295.1 h^?1) and low E_a value of 36.6 ± 2 kJ/mol for DMAB dehydrocoupling. Another important fact about the prepared catalyst is the reusability of the catalyst was very high and easily reused five times without any significant decrease in their catalytic performance. In the current work, the synthesize, characterization and the catalytic performance of the Pd–Ir nanoparticles for the dehydrogenation of the DMAB reaction will be discussed in detail.     

Defects-rich graphene/carbon quantum dot composites as highly efficient electrocatalysts for aqueous zinc/air batteries

The development of metal-free electrocatalysts for the oxygen reduction reaction (ORR) has great influence on many energy conversion devices. In present study, a highly efficient defect-rich graphene/carbon quantum dot composite was successfully obtained and employed as an advanced electrocatalyst for zinc/air batteries. To create more active sites to enhance the performance, one of the most important methods is to form defects in carbon matrix. Other methods are activation process. Here, a defect-rich graphene quantum dots (GQDs) was employed and integrated in the graphene matrix in the first hydrothermal process. Moreover, the following melamine activation during the heat treatment was executed to further fabricate defects on the surface of carbon materials. By innovative combination of the effective two methods, defects-rich carbon composite was synthesized, which lead to an excellent electrocatalytic activity for oxygen reduction reaction, indicative of great potential in the application of zinc/air batteries.     

Bimetallic Fe–Co chalcogenophosphates as highly efficient bifunctional electrocatalysts for overall water splitting

Fabrication of multicomponent materials is the most effective strategy to develop high-performance multifunctional catalysts. In this work, a series of bimetallic Fe–Co chalcogenophosphates were facilely prepared and used as bifunctional water electrolysis catalysts. The results have shown that the obtained catalysts showed high performances for hydrogen and oxygen evolution reactions, and overall water splitting. For the optimum catalyst, only 260 and 365 mV of overpotential for HER and OER, and 1.59 V of cell voltage for water splitting was needed respectively in 1 M KOH when 10 mA cm^?2 of current density was reached. High stability and Faraday efficiency were also obtained, and the obtained results confirm that the catalyst is competitive in application in water electrolysis.     

Ru@Pt core–shell nanoparticles for methanol fuel cell catalyst: Control and effects of shell composition

The present work presents a method to encapsulate pre-synthesised Ru nanoparticles (NPs) by Pt using a polyol method without capping agents at various pH values (6, 7, 8 and 10). The structural and surface properties of the catalysts were characterised using X-ray diffraction, transmission electron microscopy, CO stripping, and energy-dispersive X-ray spectroscopy. The studies suggest that the pH during encapsulation of Ru by Pt plays an important role in controlling of shell composition. A core–shell catalyst with an alloy shell was obtained at a pH of 6, whereas a monometallic Pt shell was obtained at a pH of 10. The core–shell catalysts gave higher steady-state current for methanol oxidation: 10-fold higher for alloy shells and 5-fold higher for Pt-enriched shells compared to the pure Pt catalyst. It is suggested that the highest catalytic enhancement of the core–shell catalysts is obtained through the bi-functional character that dominates the alloy shells rather than the ligand-effect-promoted Pt-enriched shells.     

Hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticles for highly efficient methanol electrooxidation

Exploiting highly efficient electrocatalysts through simple methods is very critical to the development of energy conversion technologies. Herein, we develop a hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticle catalyst (Pt–Cu/RGO) by a facile one-step electrodeposition of graphene oxide in the presence of H₂PtCl₆ and copper ethylenediamine tetraacetate. The nanostructure and composition were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Meanwhile, the electrocatalytic performance was investigated by cyclic voltammetry and chronoamperometry, showing that the Pt–Cu/RGO catalyst not only equips with an outstanding electrocatalytic activity for the methanol oxidation reaction (2.3 times that of commercial Pt/C catalyst), but also shows a robust durability and superior tolerance to CO poisoning. The excellent electrocatalytic performance could be attributed to the three-dimensional hierarchical structure, porous dealloyed nanoparticles and synergistic effect between each component.     

Polypyrrole supported Co–W–B nanoparticles as an efficient catalyst for improved hydrogen generation from hydrolysis of sodium borohydride

Effective and reusable catalysts with high performance are essentially necessary for NaBH₄ based on-demand hydrogen generators to the widespread use for energy conversion in fuel cell power systems. Herein, we report a facile synthesis of surfactant-directed polypyrrole-supported Co–W–B nanoparticles as a robust catalyst for efficient hydrolysis of NaBH₄ reaction. This non-noble metal catalyst provides much higher catalytic activity than a conventional cobalt boride catalyst. By incorporating tungsten to catalyst composition and tuning molar ratio of W/(Co + W), about a four-fold higher hydrogen generation rate was attained compared to bare Co–B. Among the all catalysts tested, Co–W–B/PPy with 7.5% W possessed the remarkable catalytic performance of 9.92 L min^?1 g^?1 and high stability over five cycles with the apparent activation energy of 49.18 kJ mol^?1.     

In-situ transformation of electrodeposited W–Co oxide to ZnCo2O4 nanoparticles as an effective bifunctional catalysts in Zn-air batteries

W–Co was cathodically electrodeposited on gas diffusion layer (GDL) electrodes for application as a bifunctional catalyst for Zn-air batteries. The electrodes were synthesized galvanostatically at various pH values (4.5 and 7.5) and deposition times (5, 15 and 25 min). Transmission electron microscopy (TEM) analysis showed that the deposits oxidized in contact with air, forming a conformal layer of W–Co oxide with a thickness of ~10 nm. During battery cycling, most of the W dissolved in the electrolyte. The remaining Co oxide agglomerated, forming nanoparticles less than 100 nm in size. Zinc (present in the electrolyte as ZnO) was incorporated into the Co oxide nanoparticles. As such, the conformal layer of W–Co oxide transformed into cubic spinel ZnCo₂O₄ nanoparticles which provided excellent bifunctional catalytic activity. The W in the original deposit acted as a conduit to facilitate formation of the ZnCo₂O₄ nanoparticles. The ZnCo₂O₄ catalyst demonstrated good performance in two-electrode and three-electrode full-cell Zn-air battery tests. In three-electrode tests at 10 mA cm⁻², a round trip efficiency of 62% was achieved, exceeding the efficiency of Pt/Ru–C (61%). The final efficiencies were 59% for the three-electrode configuration (after 100 cycles). A high maximum power density of 216 mW cm⁻² was also achieved.     

Co supported on Mg–La mixed oxides as an efficient catalyst for ammonia synthesis

Ammonia presents a promising hydrogen source and energy carrier for mobile and stationary applications. The development of new and cheaper catalysts for ammonia synthesis is thus of great importance in improving the efficiency of the Haber-Bosch process. Here we report the investigation of ammonia synthesis on cobalt catalysts supported on magnesium–lanthanum mixed oxides with varying Mg/La molar ratios. Our studies revealed that the catalyst's activity is tuneable by varying the support composition, allowing an adjustment of the surface adsorption properties. Owing to the increased basicity of the support and weaker interactions between cobalt and hydrogen atoms, the catalyst supported on mixed MgO–La₂O₃ oxide with Mg/La molar ratio of 7 demonstrated the highest activity and stability for ammonia synthesis as compared to other reported cobalt catalysts.     

One-step prepared prussian blue/porous carbon composite derives highly efficient Fe–N–C catalyst for oxygen reduction

Preparation of high-efficiency oxygen reduction reaction (ORR) catalysts with abundant and inexpensive biomass materials have been a hot research topic. We use nitrogen-rich lentinus edodes and potassium ferrate (K₂FeO₄) to simultaneously activate the carbon material and prepare prussian blue (PB), and a porous carbon composite (PB/C) containing PB is synthesized. Finally, using ammonium chloride (NH₄Cl) as a nitrogen source to further synthesize a Fe–N–C catalyst (PB/CN₁T₈₀₀) containing a trace amount of Fe for ORR. Results show that the prepared PB/CN₁T₈₀₀ catalyst forms a coral-like structure, which mainly contains mesopores and possesses a large specific surface area of approximately 1582 m² g⁻¹. Moreover, the onset potential of PB/CN₁T₈₀₀ is 0.95 V, and the half-wave potential is 0.83 V, which are consistent with those of commercial Pt/C. Thus the PB/CN₁T₈₀₀ material is an ORR catalyst with excellent performance. This work provides a basis for simple and efficient conversion of rich biomass into PB/porous carbon composites to prepare highly efficient catalysts.     

Cu-MOF@Co-MOF derived Co–Cu alloy nanoparticles and N atoms co-doped carbon matrix as efficient catalyst for enhanced oxygen reduction

We prepare a series of N-containing Cu-MOF@Co-MOF core-shell templates by employing two-step feed-in pathway and then step by step calcining these materials to obtain the N-doped carbon layers encapsulated Co–Cu alloy nanoparticles as efficient catalysts for enhanced oxygen reduction. The purpose of Cu-MOF designed as core materials is to increase the number of openly active sites when the templates are calcined at high temperature. During calcining, the Cu atoms facilitate the dispersion of Co on the surface of Co–Cu alloy nanoparticles, which efficiently avoid the agglomeration of Co during carbonization. When being used as cathode oxygen reduction catalysts, the optimal Co–Cu(3:1)@CN-900 material exhibits outstanding performance that can be comparable with the 20 wt% Pt/C catalysts, and the onset potential and half-wave potential of Co–Cu(3:1)@CN-900 is 60 mV and 37 mV higher than that of monometallic Co@CN-900 catalysts, respectively. Moreover, the active sites of Co–Cu(3:1)@CN-900 catalysts are also carefully investigated.     

Three-dimensional ZnCo/MoS2–Co3S4/NF heterostructure supported on nickel foam as highly efficient catalyst for hydrogen evolution reaction

Exploring inexpensive and earth-abundant electrocatalysts for hydrogen evolution reactions is crucial in electrochemical sustainable chemistry field. In this work, a high-efficiency and inexpensive non-noble metal catalysts as alternatives to hydrogen evolution reaction (HER) was designed by one-step hydrothermal and two-step electrodeposition method. The as-prepared catalyst is composed of the synergistic MoS₂–Co₃S₄ layer decorated by ZnCo layered double hydroxides (ZnCo-LDH), which forms a multi-layer heterostructure (ZnCo/MoS₂–Co₃S₄/NF). The synthesized ZnCo/MoS₂–Co₃S₄/NF exhibits a small overpotential of 31 mV and a low Tafel plot of 53.13 mV dec^?1 at a current density of 10 mA cm^?2, which is close to the HER performance of the overpotential (26 mV) of Pt/C/NF. The synthesized ZnCo/MoS₂–Co₃S₄/NF also has good stability in alkaline solution. The excellent electrochemical performance of ZnCo/MoS₂–Co₃S₄/NF electrode originates from its abundant active sites and good electronic conductivity brought by the multilayer heterostructure. This work provides a simple and feasible way to design alkaline HER electrocatalysts by growing heterostructures on macroscopic substrates.     

CuO–NiO/Co3O4 hybrid nanoplates as highly active catalyst for ammonia borane hydrolysis

Dehydrogenation of hydrogen-rich chemicals, such as ammonia borane (AB), is a promising way to produce hydrogen for mobile fuel cell power systems. However, the practical application has been impeded due to the high cost and scarcity of the catalysts. Herein, a low-cost and high-performing core-shell structured CuO–NiO/Co₃O₄ hybrid nanoplate catalytic material has been developed for the hydrolysis of AB. The obtained hybrid catalyst exhibits a high catalytic activity towards the hydrolysis of AB with a turnover frequency (TOF) of 79.1 mol_H2 mol cat⁻¹ min⁻¹. The apparent activation energy of AB hydrolysis on CuO–NiO/Co₃O₄ is calculated to be 23.7 kJ.mol⁻¹. The synergistic effect between CuO–NiO and Co₃O₄ plays an important role in the improvement of the catalytic performance. The development of this high-performing and low-cost CuO–NiO/Co₃O₄ hybrid catalytic material can make practical applications of AB hydrolysis at large-scale possible.     

Polymer-graphene hybride decorated Pt nanoparticles as highly efficient and reusable catalyst for the dehydrogenation of dimethylamine–borane at room temperature

Addressed herein, we report a reduced graphene oxide (rGO) nanosheet coupled with polyaniline (PANI) for platinum (Pt) nanoparticles as supporting materials. The PANI-coupled rGO (PANI@rGO) nanosheet is prepared by a simple one-step chemical assembly strategy, and Pt nanoparticles are anchored on the support of PANI@rGO through the reaction of PANI with a platinum salt. The designed PANI efficiently exposes the surface of rGO sheets and stabilizes metal nanoparticles. Consequently, the Pt@PANI-rGO catalyst exhibits good reusability, durability and high catalytic performance for dimethylamine–borane dehydrogenation reaction. The structure morphology and properties of Pt@PANI-rGO NPs were characterized by using several different techniques such as UV–Vis, XPS, TEM, XRD and HR-TEM-EDX analyses. This newly prepared catalyst can be reused again at low concentrations and temperature. They showed a high turnover frequency (42.94 h^?1) and low E_a value of 15.1 ± 2 kJ/mol for DMAB dehydrocoupling in the ambient conditions. The proposed nano architecture offers a new pathway to promote the performances of rGO in various applications; moreover, this work provides a powerful and universal synthetic strategy for such an architecture.     

Co–Co3O4 nanostructure with nitrogen-doped carbon as bifunctional catalyst for oxygen electrocatalysis

In view of the development of advanced bi-functional oxygen electrodes for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), herein, we report the synthesis of Co–Co₃O₄ nanostructure encased in N-doped carbon (Co–Co₃O₄/NC) by carbothermal reduction followed by controlled oxidative treatment. The formation of a protective-active oxide layer on the metallic-Co not only facilitated the effective charge separation and transport but also displayed improved stability of Co–Co₃O₄/NC in an alkaline operating condition. The Co–Co₃O₄/NC catalyst afforded 0.810 V overvoltage between ORR and OER in 0.1 M KOH solution, consequently, this lower reversible overvoltage would result in energy saving of around 0.246 V if Co–Co₃O₄/NC is used as an oxygen electrode instead of commercially available 40 wt % Pt/C. Furthermore, in comparison with the use of Pt/C + IrO₂ as an ORR and OER catalyst, respectively the single bi-functional electrocatalyst i.e., Co–Co₃O₄/NC would result in energy saving of around 0.13 V.     

Graphite–FeSi alloy composites as anode materials for rechargeable lithium batteries

Iron–silicon are prepared by annealing elemental mixtures at 1000 °C followed by mechanical milling. Graphite–Fe₂₀Si₈₀ alloy composites have been prepared by ball-milling a mixture of Fe₂₀Si₈₀ alloy and graphite powder. The microstructure and electrochemical performance of the composites are characterized by X-ray diffraction and an electrochemical method. The FeSi₂ matrix is stable for extended cycles and acts as a buffer for the active centre, Si. The Fe₂₀Si₈₀ alloy electrode delivers large initial capacity, but the capacity degrades rapidly with cycling. Fe₂₀Si₈₀ alloy–graphite composite electrodes, however, show good cycleability and a high reversible capacity of about 600 mAh g⁻¹. These composites appear to be promising candidates for negative electrodes in lithium rechargeable batteries.     

Monodisperse nickel–palladium alloy nanoparticles supported on reduced graphene oxide as highly efficient catalysts for the hydrolytic dehydrogenation of ammonia borane

Addressed herein is the catalysis of reduced graphene oxide-supported monodisperse NiPd alloy nanoparticles (NPs) (rGO-NiPd) in the hydrolytic dehydrogenation of ammonia borane (AB). This is the first example of the use of NiPd alloy NPs as catalyst in the hydrolytic dehydrogenation of AB. Monodisperse NiPd alloy NPs (3.5 nm) were synthesized by co-reduction of nickel(II) acetate and palladium(II) acetylacetonate in oleylamine (OAm) and borane-tert-butylamine complex (BTB) at 100 °C. The current recipe allowed to control the composition of NiPd alloy NPs and to study the composition-controlled catalysis of rGO-NiPd in the hydrolytic dehydrogenation of AB. Among the all compositions tested, the Ni₃₀Pd₇₀ was the most active one with the turnover frequency of 28.7 min⁻¹. The rGO-Ni₃₀Pd₇₀ were also durable catalysts in the hydrolytic dehydrogenation of AB providing 3650 total turnovers in 35 h and reused at six times without deactivation. The detailed reaction kinetics of hydrolytic dehydrogenation of AB revealed that the reaction proceeds first order with respect to the NiPd concentration and zeroth order with respect to the AB concentration. The apparent activation energy of the catalytic dehydrogenation of AB was also calculated to be E_a^app = 45 ± 2 kJ*mol⁻¹.     

Pd decorated Co–Ni nanowires as a highly efficient catalyst for direct ethanol fuel cells

The storage and conversion of energy necessitates the use of appropriate electrochemical systems and chemical reaction catalysts. This work presents newly developed catalysts for electrooxidation of ethanol in an alkaline medium. Nanocatalysts composed of Co–Ni nanowires (Co–Ni NWs) decorated with Pd nanoparticles (Pd NPs) were made at varying metal ratios and their chemical composition and structure was investigated in detail. The synthesis involved a wet chemical reduction assisted by a magnetic field, which led to the generation of NWs, followed by the deposition of spherical Pd NPs on their surface. The best catalytic activity was obtained for the catalyst made of Co₃–Ni₇ decorated with Pd NPs, which exhibited EOR of 8003 mA/mg_Pd for only 0.86 wt% of Pd loading. The results can be explained by the synergistic effect between the morphology of the bimetallic support and the favorable interaction of oxophilic Co, Ni with catalytic Pd.