Highly branched PtCu nanodandelion with high activity for oxygen reduction reaction

A facile hydrothermal route has been developed to synthesize the highly branched Pt₅₈Cu₄₂ nanoparticles via mixing the H₂PtCl₆ and CuCl₂ with octadecylamine. The Pt₅₈Cu₄₂ after post treatment forms a dandelion flower 3-D structure. A combination of both the branched shape and PtCu composition effects in the Pt₅₈Cu₄₂-nanoparticles shows superior electrocatalytic activity and durability to commercial Pt black for oxygen reduction reaction. The mechanism for the de-alloying and reconstructing of the Pt₅₈Cu₄₂-nanoparticles in electrochemical activity and durability tests has been proposed. It is found that after the durability process, the Pt₅₈Cu₄₂ precursor alloy changes into a substantially Pt enriched PtCu alloy (Pt₇₉Cu₂₁) with a Pt skin. The Pt skin effectively prevents the further dissolution of the Cu below the near-surface to enhance its durability. What's more, the Pt skin exposed to (111) planes which have the lowest surface energy among the low-index planes further promotes the improvement of durability of the PtCu catalyst.     

KOH-activated multi-walled carbon nanotubes as platinum supports for oxygen reduction reaction

In the present investigation, multi-walled carbon nanotubes (MWCNTs) thermally treated by KOH were adopted as the platinum supporting material for the oxygen reduction reaction electrocatalysts. FTIR and Raman spectra were used to investigate the surface state of MWCNTs treated by KOH at different temperatures (700, 800, and 900 °C) and showed MWCNTs can be successfully functionalized. The structural properties of KOH-activated MWCNTs supported Pt were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and their electrochemical performance was evaluated by the aid of cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry. According to the experimental findings of the present work, the surrface of MWCNTs can be successfully functionalized with oxygen-containing groups after activation by KOH, favoring the good dispersion of Pt nanoparticles with narrow size distribution. The as-prepared Pt catalysts supported on KOH treated MWCNTs at higher temperature, possess higher electrochemical surface area and exhibit desirable activity towards oxygen reduction reaction (ORR). More precisely, it has been found that the electrochemical active area of Pt/MWCNTs-900 is approximately two times higher than that of Pt/MWCNTs. It can be concluded that KOH activation is an effective way to decorate MWCNTs’ surface with oxygen-containing groups and bigger surface area, which makes them more suitable as electrocatalyst support materials.     

Thermal decomposition behavior of nickel-iron hydrotalcite and its electrocatalytic properties of oxygen reduction and oxygen evolution reactions

The thermal decomposition behavior of NiFe layered double hydroxide (LDH) was investigated by thermogravimetric analysis-differential scanning calorimetry (TG-DSC). The calcined product at 500 °C was mainly NiO/FeOx composite oxide, of which FeOx was amorphous oxide; the calcined product at 650 °C was mainly NiO/NiFe₂O₄ composite oxide. The polarization curves and chronopotentiometry stated that the NiO/FeOx and NiO/NiFe₂O₄ showed good electrocatalytic OER and ORR activity; the OER activity of NiO/FeOx was better than that of NiO/NiFe₂O₄; the ORR activity of NiO/NiFe₂O₄ was better than that of NiO/FeOx.     

Self-supported Ni2P nanotubes coated with FeP nanoparticles electrocatalyst (FeP@Ni2P/NF) for oxygen evolution reaction

Bimetallic phosphides have been widely investigated as electrocatalysts for oxygen evolution reaction (OER) due to their efficient activity and environmental friendliness. While the reasonable design and controllable synthesis of bimetallic phosphide with typical nanostructure is still a great challenge. Hence, we put forward a novel and straightforward way for constructing FeP nanoparticles coated Ni₂P ultrathin nanotube arrays on the surface of Ni foil (FeP@Ni₂P/NF), which is synthesized through two steps of electrodeposition and subsequent in-situ phosphorization process. The obtained FeP@Ni₂P/NF shows excellent electrochemical activity for OER, and it only needs potential of 1.52 V vs. RHE to reach the current density of 50 mA cm⁻² in an alkaline media. The excellent electrocatalytic activity of FeP@Ni₂P/NF mainly benefits from: (i) the synergistic effect between FeP and Ni₂P promoting electron transfer; (ii) the formation of the unique 3D ultrathin nanotube arrays increasing the quantity of active sites and avoiding the agglomeration of catalysts during testing. In addition, the influence of reaction condition on the electrochemical activity for OER has also been investigated through altering the phosphorization temperature of precursor.     

Facile synthesis of copper selenide with fluffy intersected-nanosheets decorating nanotubes structure for efficient oxygen evolution reaction

Rational nanostructure design is the key point to prepare catalysts with superior catalytic performance, and tedious preparation method limits them large-scale application. Here, a Cu₂Se with fluffy intersected-nanosheets decorating nanotubes structure were prepared by a simple and rapid solution-immersion method at room temperature. The hollow hierarchical structure on a good conductor Cu foam (CF) enlarges surface available sites, enhances the conductivity of electrode materials, then endowing the catalyst with quick charge/mass transportation and favorable oxygen evolution reaction (OER) performance. In alkaline medium, our as-prepared Cu₂Se/CF electrode demonstrates high OER performance, especially for lower overpotential (200 mV at 10 mA cm⁻²) compared with the previously reported Cu-based catalysts. Moreover, the Cu₂Se catalyst could afford galvanostatic test of 10 mA cm⁻² test over 12 h and present superior OER tolerance. These results indicate that the Cu₂Se catalyst via cost efficiency and efficient solution-immersion method could be applied to large-scale efficient OER.     

Nitrogen-doped carbon nanotubes with high activity for oxygen reduction in alkaline media

Nitrogen-doped carbon nanotubes (NCNTs) were prepared using a floating catalyst chemical vapour deposition method. The multiwalled NCNT contains 8.4 at% nitrogen and has a dimension of 100 nm in the diameter and 10-20 nm in the wall thickness. The catalytic activity and durability of the NCNTs towards oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) techniques in KOH solution. In addition, the effects of KOH concentration on several ORR performance indicators of the NCNT catalyst, such as the number of electrons transferred, the diffusion-limiting current density, the onset and half-wave potentials, were also examined in electrolytes of various KOH concentrations, ranging from 0.1 to 12 M. Experimental results show that NCNTs exhibited comparable activity for ORR in alkaline electrolyte as compared with commercially available Pt/C catalyst, and much higher activity than commercial Ag/C catalysts. In addition, the NCNTs showed good stability from the potential cycling test, and the concentration of KOH had significant impact on the ORR performance indicators of the NCNT catalysts.     

PtCu nanoframes as ultra-high performance electrocatalysts for methanol oxidation

Despite tremendous progress has been achieved in the past two decades, the lack of high-performance catalysts suitable for long-term operation remains a great challenge in realizing the commercial application of direct methanol fuel cell technology. Here, we reported a simple approach for one-pot synthesis of PtCu alloy nanoframes along with their exciting electro-catalytic performance for methanol oxidation. PtCu alloys with highly-open nanoframe structures have been achieved in presence of a structure-directing agent like polyvinyl pyrrolidone (PVP) and reducing solvent like sodium borohydride. Such PtCu alloy nanoframes show tremendous improvement in the methanol electrooxidation with a highest mass activity of 1.64 A mg_Pt ⁻¹ (much lower onset potential compared to Pt alone), which is believed to be much higher compared to that of the commercial Pt/C catalyst and most of the literature reports, indicating a better alloy formation and highly active sites created by highly open nanoframes structures.     

Architecture of porous CoS1.097-C composite nanowire for efficient oxygen reduction reaction

Design and preparation of efficient and low cost electrocatalysts for the oxygen reduction reaction (ORR) is vitally important for the commercialization of alkaline direct methanol fuel cell (ADMFC). Herein, porous CoS_1.097-C composite nanowire is prepared by one-step in-situ pyrolyzing Co-nitrilotriacetic acid (Co-NTA) precursor in Ar atmosphere with adding S powder. The obtained CoS_1.097-C composite nanowire gathered by carbon encapsulated CoS_1.097 nanoparticles are further analyzed by FT-IR, XRD, SEM, TEM, Raman, BET and XPS. The optimized CoS_1.097-C composite nanowire catalyst shows the onset potential of 0.90 V and half-wave potential of 0.79 V with the acquired tafel slope of 57.7 dec⁻¹ for ORR in 0.1 M KOH. Further studies indicate that the effective four-electron pathway contributes to excellent ORR activity. Moreover, the CoS_1.097-C composite nanowire catalyst exhibits good durability and methanol tolerance over the commercial Pt/C. This work provides a general strategy for developing carbon-based transition metal sulfide nanocomposite as cathode in ADMFC.     

Facile synthesis of Pd supported on Shewanella as an efficient catalyst for oxygen reduction reaction

While noble metals loaded on carbon-based supports are commonly used as oxygen reduction catalysts for fuel cell cathodes, the preparation process is complicated and expensive cost. In this paper, Pd²⁺ was first adsorbed on Shewanella by its adsorption characteristics, then the Pd supported on Shewanella catalyst was obtained after carbonization at 600 °C and hydrogen reduction at 200 °C. The Shewanella cells retain the rod shape of bacteria following pyrolysis under high temperatures, while N and Pd heteroatoms are uniform distribution on the carbon matrix. As a result, Pd supported on Shewanella catalyst exhibits excellent electrocatalytic activity for ORR via a dominant four-electron oxygen reduction pathway in alkaline medium. More importantly, the mass activity of the prepared catalyst was 5.8 times higher than that of commercial Pd/C, and its stability was also better than the Pd/C, which could be promising alternatives to costly Pt-based electrocatalysts for ORR.     

In-situ facile synthesis of heterostructural Co||MnCo2O4.5/NC with active oxygen vacancies and its bifunctional electrocatalysis for oxygen reduction and oxygen evolution reaction

A potential non-noble metal oxide catalyst with its low-cost and efficient catalytic ability attract increasing attention. In this paper, a highly efficient bifunctional electrocatalyst Co||MnCo₂O_4.5/NC with heterostructure and oxygen vacancies is prepared utilizing solid reaction in-situ. The optimal catalyst is obtained at 650 °C with the mass ratio (1:8) of MnCo₂O_4.5 and Dicyandiamide (DCD). It shows excellent electrocatalytic activity for oxygen reduction reaction (ORR) with high half-wave potential (0.81 V) and limit current density (6.22 mA cm^?2), which is better than that of the commercial 20% Pt/C(0.81 V, 5.52 mA cm^?2). At the same time, it also exhibits superior electrocatalytic activity for oxygen evolution reaction (OER) with low overpotential (330 mV) and a faster dynamics process. The superior electrocatalytic properties may be resulted from the presence of heterostructure and increasing ratio of oxygen vacancies, which helps to the rapid transfer of electrons and creates more active sites. Moreover, the self-generated N-doped carbon provides high conductivity of the as-prepared Co||MnCo₂O_4.5/NC composite. It can be seen that the application of interface engineering technologies is useful for improving the performance of the catalyst, providing an effective and facile synthesis strategy for non-noble metal catalyst.     

Readily fabricated NiCo alloy-metal oxide-carbon black hybrid catalysts for the oxygen reduction reactions in the alkaline media

Highly efficient, cost-effective and environmental-friendly electrocatalysts play a crucial role in oxygen reduction reaction (ORR) for fuel cells and metal-air batteries. Herein, a series of hybrids comprising of NiCo alloy, metal oxides and carbon black were readily prepared by a one-pot pyrolysis approach and employed as efficient ORR electrocatalysts in the alkaline media. Different amounts of Ketjen Black EC 300J (EC) with a large mesoporous area and exceptional electrical conductivity were directly added to synthesize the hybrids. Among the hybrids tested, the NC-MMO-EC-3 (where NC stands for NiCo alloy and MMO for mixed metal oxides) with an appropriate amount of EC displayed the best ORR electrochemical activity. The enhanced activity of the NC-MMO-EC-3 could be attributed to the conductivity improved by EC, the high dispersion of MMO and NC on EC support, and the beneficial interaction among those three components.     

Three-dimensional porous PtCu as highly efficient electrocatalysts for methanol oxidation reaction

Exploring affordable, durable, and effective electrocatalysts for methanol oxidation reaction (MOR) is of great importance to the industrial application of direct methanol fuel cells. Herein, a three-dimensional (3D) porous PtCu catalyst is synthesized by a facile and effective galvanic replacement method, which exhibits high activity and durability for MOR. The modulated electronic and strain effects of the Pt atoms are verified by extensive characterizations, and the mass and specific activities of the prepared catalyst are roughly 3.8 and 9.9 times higher than those of the commercial Pt/C catalysts, respectively. The robust activity of the prepared catalyst is probably owing to the optimized affination between Pt and the adsorbed poisoning species (mainly CO) induced by the electronic and strain effects of the Pt, as well as the unique 3D porous nanostructure.     

Monodisperse PtCu alloy nanoparticles as highly efficient catalysts for the hydrolytic dehydrogenation of ammonia borane

Pt-M alloy nanoparticles (NPs) with well-defined size and compositions exhibit dramatically catalytic performance in chemical reactions. In this work, monodisperse PtCu NPs with controlled size and compositions were synthesized by the co-reduction method in the presence of oleylamine. These NPs have excellent catalytic activities in the hydrolytic dehydrogenation of ammonia borane (AB) and their activities were composition dependent. Among the different-composition PtCu NPs, the Cu₅₀Pt₅₀ NPs exhibit the highest catalytic activity with an initial turnover frequency of 102.5 mol_(hydrogen)·mol_(catalyst)^?1·min^?1 and an apparent activation energy of 36 kJ·mol^?1, which demonstrate the validity of partly replacing Pt by a first-row transition metal on constructing high performance heterogeneous nanocatalysts for the hydrolytic dehydrogenation of AB.     

Durability of de-alloyed PtCu/C electrocatalysts

Durability is one of the most important characteristics of electrocatalysts used in low-temperature fuel cells with a proton exchange membrane. The degradation degree of deposited electrocatalysts containing platinum and platinum-copper nanoparticles with Pt-loading of about 20% by weight was assessed by voltammetric stress-testing, which corresponded to different mechanisms of degradation. The differences in the PtCu nanoparticles architecture, caused by the peculiarities in their synthesis, affect the catalysts stability and their composition change due to the stress tests.It has been shown that at the close values of Pt-loading and electrochemically active surface area (ESA), the bimetallic catalysts on the Vulcan XC72 carbon carrier demonstrate significantly higher stability compared to commercial Pt/C catalysts. In this case, the “gradient” catalyst obtained by successive multi-stage copper and platinum deposition showed the highest residual activity in ORR, as well as resistance to stress testing and to the copper selective dissolution.     

Tin-nitrogen/carbon for superior oxygen reduction reaction at fuel cell cathode

This work reports on the synthesis of tin-nitrogen/carbon (Sn–N/C) catalysts suitable for the electroreduction of molecular oxygen at the cathode of proton exchange membrane fuel cells. The catalysts were synthesized through a simple pyrolysis process of folic acid as the carbon and nitrogen source, tin chloride as a tin source and Vulcan carbon as the substrate. The synthesized catalyst exhibited excellent oxygen reduction activity with a half wave potential of 0.82 V and a mass activity of 15.5 mA mg⁻¹. Successful application at the cathode of a self-breathing fuel cell further confirmed the superior performance of this catalyst leading to a power density of 29.4 mW cm⁻². This is very comparable to the reference platinum/Vulcan carbon catalyst (28.4 mW cm⁻²). In addition, this Sn–N/C catalyst showed good stability under accelerated stress tests with only a 12% decrease in fuel cell performance after 10,000 cycles. The superior performance was assumed to be due to the presence of both metal-nitrogen and nitrogen-carbon active sites, which facilitate the four-electron path of the oxygen reduction reaction.     

Encapsulated spinel CuXCo3-XO4 in carbon nanotubes as efficient and stable oxygen electrocatalysts

The development of efficient, stable and cost-effective electrocatalysts for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER), have become one of the most important bottlenecks in pursuing emerging renewable energy storage and environment friendliness technologies. In this study, we have successfully developed encapsulated Cu_XCo_3-XO₄ spinel nanocrystals in carbon nanotubes as high-performance bifunctional oxygen electrocatalyst by one-step hydrothermal reaction. As compared with other Co-based materials, the resulting Cu_XCo_3-XO₄@C composite presents excellent catalytic performance and outstanding stability for both OER and ORR with ultralow overpotential (η = 0.358 V) at a current density of 10 mA/cm² and half-wave potential (E_1/2 = 0.82 V) in alkaline solution, respectively. The developed strategy to encapsulate spinel into carbon nanomaterials via a controllable pathway, may open new opportunities for the encapsulation structures of other catalysts.     

Nitrogen and sulfur doped ZnAl layered double hydroxide/reduced graphene oxide as an efficient nanoelectrocatalyst for oxygen reduction reactions

In this work, to synthesize an efficient and low-cost electrocatalysts for Oxygen Reduction Reaction (ORR), the combination of N,S-rGO and ZnAl-LDH with several concentrations is studied for the first time. For this purpose, six electrocatalysts including Graphene Oxide (GO), functionalized reduced graphene oxide with nitrogen and sulfur atoms (N,S–rGO), Zinc–Aluminum layered double hydroxides (ZnAl-LDH), and ZnAl-LDH/N,S–rGO hybrids in three weight ratios of 1:1, 1:3, and 1:5 (the weight ratio of N,S-rGO is 1) are synthesized by the hydrothermal method. The physical properties, morphology, and structure of the synthesized electrocatalysts are determined by using X-Ray Diffraction (XRD) analysis, Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Analysis (EDX), the Fourier Transform Infrared Spectroscopy (FTIR) and Raman analysis. Electrochemical measurements are implemented by using Cyclic Voltammetry (CV), Linear Scanning Voltammetry (LSV), and chronoamperometric. Also, the electron transfer number is calculated by K-L plot. The obtained results for all samples are compared with the %20 Pt/C commercial catalyst. Based on the results of the physical tests, in addition to the uniform distribution and the correct deposition of the synthesized electrocatalysts, the particle size also reached the nanometer range. According to the electrochemical results, among the synthesized electrocatalysts, the ZnAl-LDH/N,S–rGO with 1:1 wt ratio has the best electrochemical activity. This result indicates a well synergistic and interaction effect between N,S–rGO and ZnAl-LDH for the ORR. The onset potential is obtained to be −0.01 V vs Ag/AgCl. The average of electron transfer number by this electrocatalyst is 3.60, which indicates that it is close to the 4e pathway for the ORR. The electrocatalytic stability was favorable in the alkaline medium. It can be concluded that the Layered Double Hydroxides (LDHs) improve the electrical conductivity, the electrocatalytic activity, the active surface area, and the stability for the oxygen reduction reaction after the combination with carbon bases. To be clear, the combination of N,S-rGO and ZnAl-LDH with several concentrations has been investigated for the first time on the ORR applications. The sensitivity analysis is implemented to determine the optimal concentration. This study proposes a new approach for using N, S-rGO composite to improve the low electron conductivity of LDHs.     

Synthesis of ultrathin-wall PtCu nanocages as efficient electrocatalyst toward oxygen reduction reactivity

Pt-based hollow nanocrystals have shown an astonishing performance toward oxygen reduction reaction (ORR) because of their open structures, high surface areas and large Pt atom utilization. However, the careful geometric control of hollow nanocrystals is still not easy. Here, a facile template-free method was reported for the synthesis of ultrathin-wall PtCu nanocages with small islands on the surface (U–PtCu NCs). Moreover, the wall thickness of nanocages and the density of islands were well-tuned by controlling the experiment conditions. In the end, the novel hollow structures with abundant defects as well as the synergistic interaction between Pt and Cu elements endowed U–PtCu NCs with enhanced ORR activity. Specifically, its mass activity was 0.36 A mg⁻¹ and its specific activity was 0.71 mA cm⁻², which were about 4.2 and 7.1 times higher than that of commercial Pt/C. In addition, the enhanced stability was proved by the accelerated durability test of 10 000 cycles.     

Co-Fe/MIL-101(Cr) hybrid catalysts: Preparation and their electrocatalysis in oxygen reduction reaction

The development of highly efficient electrocatalysts with low cost for oxygen reduction reaction (ORR) is urgently required for metal-air batteries and fuel cells. In this work, FeCo/MIL-101(Cr) with various molar ratios of Fe/Co as hybrid catalysts was prepared by a facile and mild impregnation method. MIL-101(Cr) increased the specific surface areas of the hybrid catalysts, thus improving the dispersion of Fe and Co species at their surfaces. The effects of Fe and Co species on ORR activity of the hybrid catalysts were investigated. It is found that the synergistic effects between the well-dispersed Fe and Co species contribute mainly to ORR activity. More specifically, Fe species exert a partial-charge-transfer-activation effect on Co ones, which reduces the charge transfer resistance and thus improves the catalytic activity. As a result, FeCo/MIL-101(Cr) showed the excellent ORR activity, in which Co₅₀Fe₅₀/MIL-101(Cr) exhibited the superior ORR activity to the other prepared hybrid catalysts.