Ternary Nanocatalysts Research Articles

Spontaneous incorporation of gold in palladium-based ternary nanoparticles makes durable electrocatalysts for oxygen reduction reaction.

Replacing platinum by a less precious metal such as palladium, is highly desirable for lowering the cost of fuel-cell electrocatalysts. However, the instability of palladium in the harsh environment of fuel-cell cathodes renders its commercial future bleak. Here we show that by incorporating trace amounts of gold in palladium-based ternary (Pd6CoCu) nanocatalysts, the durability of the catalysts improves markedly. Using aberration-corrected analytical transmission electron microscopy in conjunction with synchrotron X-ray absorption spectroscopy, we show that gold not only galvanically replaces cobalt and copper on the surface, but also penetrates through the Pd–Co–Cu lattice and distributes uniformly within the particles. The uniform incorporation of Au provides a stability boost to the entire host particle, from the surface to the interior. The spontaneous replacement method we have developed is scalable and commercially viable. This work may provide new insight for the large-scale production of non-platinum electrocatalysts for fuel-cell applications.

Influence of Nanostructured Carbon Supports on Nanocatalysts Towards Electrooxidation of Formic Acid for Direct Formic Acid Fuel Cells

Direct formic acid fuel cells (DFAFCs) have been reported as a prominent source of alternative green energy and solution to imminent energy crisis for the last two decades. The challenge to commercialize DFAFCs is mainly the utilization of cost effective, high performance and durable anodic catalyst for electrooxidation of formic acid (HCOOH). Low metal loading, high surface area, good electrical conductivity, excellent stability in acidic and alkaline media, and easy availability make nanostructured carbon supports attractive for fuel cell applications. We report here the comparative studies of three different carbon based support materials and their influence on catalytic activities towards the electrochemical oxidation of HCOOH using mono (20 wt% Pd) and ternary (10 wt% Pd-Ni-Co) composite nano-catalysts with commercial 20 wt% Pd/C (activated carbon, ~500 m2g-1). The nano-catalysts were synthesized using Pd2+, Ni2+ and Co2+ precursors using Vulcan-XC72 (250 m2g-1, <50 nm), Ketjen Black (1400 m2g-1) and graphite nano-particles (GNP) (~10 nm) support materials and NaBH4 as reducing agent. The electrochemical oxidation of HCOOH was conducted at a glassy carbon disk electrode (GCE, 3 mm diameter) pre-casted with 9 µL of each catalyst ink covered with 3 µL Nafion® polymer (5 wt%) in 0.50 M HCOOH-0.10 M H2SO4. The catalytic oxidation behavior of HCOOH of all the catalysts was compared using cyclic voltammetry. Multi-potential step chronoamperometry (CA) was utilized for stability tests. The catalytic behavior of all the ternary nano-catalysts is believed to be ascribed to the direct oxidation pathway of HCOOH as indicated by the oxidation peak potential of ~ -0.2 V vs Hg/Hg2SO4 (satd. K2SO4) reference electrode. In contrast, the synthesized mono catalysts and commercial Pd/C showed both direct and indirect oxidation pathways. The use of Ni and Co also showed synergistic effect as the HCOOH oxidation peak potential was shifted negatively by ~200 mV with respect to that of the commercial catalyst containing even doubled amounts of Pd. Furthermore, CA data showed that GNP and Ketjen Black supported catalysts were almost as stable as the commercial Pd/C, although the electrooxidation current at the Vulcan-XC72 based catalysts decreased by ~50% within about 20 min. On the other hand, Vulcan-XC72 supported catalysts showed the highest HCOOH oxidation current and the rest were in close proximity to one another. Finally, morphology and elemental analyses employing scanning electron microscope and energy dispersive X-ray spectroscopy revealed the different catalytic activity on various support materials were concordant with the electrochemical data as the turbostratic substrates contributed better metal dispersion and uniform size distribution. Financial support from the CAREER Award (CHE-0955878) is gratefully acknowledged.

A ternary nanocatalyst of Ni/Cr/Co oxides with high activity and stability for alkaline glucose electrooxidation

A novel ternary nanocatalyst of Ni-Cr-Co oxides is synthesized as anode electro-catalysts for glucose oxidation. The nanostructure is characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), which indicates that the catalyst particles are well dispersed with average size of 30nm when the calcination temperature is 500°C. The electrochemical performance is evaluated via cyclic voltammetry (CV). Compared with the bimetallic Ni-Cr and Ni-Co nanocatalysts, Ni-Cr-Co electrocatalysts exhibites more negative onset potential (0.4V) and high oxidation peak current density (23.8mAcm−2) in alkaline media towards glucose oxidation. Meanwhile, the results also show that the Ni-Cr-Co nanomaterial possesses good performance of anti-poisoning capability, reproducibility and long-time stability, which make it an excellent candidate for fuel cell electrocatalyst.

Ternary dendritic nanowires as highly active and stable multifunctional electrocatalysts.

Multimetallic nanocatalysts with a controlled structure can provide enhanced catalytic activity and durability by exploiting electronic, geometric, and strain effects. Herein, we report the synthesis of a novel ternary nanocatalyst based on Mo doped PtNi dendritic nanowires (Mo-PtNi DNW) and its bifunctional application in the methanol oxidation reaction (MOR) at the anode and the oxygen reduction reaction (ORR) at the cathode for direct methanol fuel cells. An unprecedented Mo-PtNi DNW structure can combine multiple structural attributes of the 1D nanowire morphology and dendritic surfaces. In the MOR, Mo-PtNi DNW exhibits superior activity to Pt/C and Mo doped Pt dendritic nanowires (Mo-Pt DNW), and excellent durability. Furthermore, Mo-PtNi DNW demonstrates excellent activity and durability for the ORR. This work highlights the important role of compositional and structural control in nanocatalysts for boosting catalytic performances.

Oxygen reduction reaction at binary and ternary nanocatalysts based on Pt, Pd and Au

Carbon-supported monometallic, binary and ternary nanocatalysts based on Pt, Pd and Au were synthesized by a “water in oil” microemulsion method and characterized by atomic absorption spectrometry, thermogravimetry, transmission electron microscopy, X-ray diffraction, and electrochemical methods. A comparative study of the oxygen reduction reaction on monometallic, alloyed binary and ternary nanocatalysts has been performed. The catalytic activity and the selectivity of the nanocatalysts towards the ORR have been determined by rotating disc electrode and rotating ring disc electrode in O2-saturated 0.1M HClO4 electrolyte. It was shown that the addition of palladium to platinum led to a constant decrease of the activity with the Pd ratio. The modification of platinum by gold allows improving the activity of the catalyst towards ORR for gold ratio up to 50at%. Ternary Pt70Pd15Au15/C and Pt50Pd25Au25/C were synthesized. These catalysts showed improved catalytic activities towards ORR. Aging tests have been carried out, showing that a part of the loss in the activity of gold containing catalysts is due to gold segregation from the bulk to the surface of nanoparticles.

Binary and Ternary Catalysts Based on Pt, Au and Ni for the Oxygen Reduction Reaction

Proton exchange membrane fuel cells (PEMFC) are currently considered as an alternative to fossil fuels for transportation, stationary, aeronautics applications1… However, the activation of oxygen reduction reaction (ORR) at the cathode of PEMFC has been and remains a key challenge to make this technology marketable. Indeed, oxygen reduction reaction has a low kinetics and requires catalyst to be activated. Platinum is known to be the most active electrocatalyst for this reaction. The disadvantages of platinum based catalysts are their high cost and low durability. Then several studies were carried out for the last decades in order to develop new catalysts both to improve the catalytic activity and the durability, and to reduce the platinum loading at the cathode. Studies indicated that structural and electronic effects involved in Pt alloys or core shell structures (with metals such as Au, Ni, Fe, Co) enhance the catalytic activity 2, 3. Recent works on Pt3M (M= Ni, Fe, Co) showed considerable improvement of catalytic activity toward the ORR4. It was also shown that the durability could significantly be improved by alloying Pt with Au. This contribution presents a comparative study of the ORR on monometallic, alloyed binary and ternary nanocatalysts based on Pt, Ni and Au. Water-in-oil microemulsion method has been implemented for synthesizing Pt/C, Au/C, PtxM1-x/C (M= Ni, Au) and PtxNiyAuz/C nanocatalysts supported on a carbon black Vulcan XC-72 support. Nanocatalysts were comprehensively characterized by atomic absorption and thermogravimetric analysis in order to determine bulk chemical compositions and metal loadings. The morphology of catalysts and the particle sizes were determined by transmission electron microscopy (TEM). X-ray diffraction (XRD) studies allowed determining their microstructure (crystallite size and alloy formation). The surface composition was determined by X-Ray photoelectron spectrometry (XPS) and electrochemical analyses. The catalytic activity and the selectivity of the nanocatalysts toward the ORR have been determined by rotating disc electrode (RDE) and rotating ring disc electrode (RRDE) in O2-saturated 0.1 M HClO4 electrolyte. It was shown that the catalytic activity of PtxAu1-x/C nanocatalysts is maintained up to 50 at % of gold in the alloy. The addition of Ni to Pt allows improving the catalytic activity in comparison to that recorded on pure Pt/C catalyst (figure 1), with an optimum for a Pt3:Ni1 ratio. Hence, different ternary PtxNiyAuz/C catalysts were synthesized keeping the Pt:Ni ratio 3:1, and their catalytic activities were determined, as well as their selectivity towards the 4-electron process. [1] C. Coutanceau, S. Baranton, “Advanced Processes in Catalytic Oxidation - Oxygen Activation in Fuel Cells and Electrocatalytic Processes”, in “From Laboratory Studies to Industrial Applications", D. Duprez and F. Cavani (Eds.), Imperial College Press, London, 2014. [2] F. H. B. Lima, J. Zhang, M. H. Shao, K. Sasaki, M. B. Vukmirovic, E. A. Ticianelli, R. R. Adzic, J. Phys. Chem. C 2007, 111, 404-410. [3] M. T. Paffet, J. G. Beery, S. Gottesfeld, J. Electrochem. Soc. 135 (1988) 1431. [4] T. Toda, H. Igarashi, H. Uchida, M. Watanabe, J. Electrochem. Soc. 1999, 146, 3750. Acknowledgement: This work was made under the framework of the SMARTCat project funded by the European Commission under the FP7 Fuel Cells and Hydrogen Joint Technology Initiative grant agreement FP7-2012-JTI-FCH-325327. Figure 1

Carbon supported Pd-Pt-Cu nanocatalysts for formic acid electrooxidation: Synthetic screening and componential functions

Carbon supported Pd-Pt-Cu trimetallic nanocatalysts for formic acid oxidation (FAO) are comparatively synthesized via different one-pot liquid-phase chemical reduction routes. Either sodium borohydride or ethylene glycol is employed as the main reducing agent, with the stabilizer opted from disodium ethylenediamine tetraacetate (EDTA), oleylamine, sodium citrate and urea. The trimetallic nanocatalyst synthesized with ethylene glycol and sodium citrate exhibits the most homogeneous nanoparticle dispersion and the highest alloying degree. Pd20Pt1Cu10/C-Cit shows the best electrocatalytic performance among all the tested electrocatalysts. Componential distributions on nanoalloy particles are distinguished through ex situ XPS, CO stripping and in situ ATR-IR measurements on interested nanocatalysts. The cheaper element Cu functions mainly as the “core filler” to expose a Pd and Pt-segregated active surface, and a deliberately controlled small fraction of Pt (versus Pd) on the surface minimizes the undesired dehydration of formic acid. In addition, a weak electronic effect from Cu and Pt may promote FAO on Pd. Surface restructuring with Pt agglomeration and partial Cu dealloying arising from a repeated potential cycling pretreatment degrades the performance of the ternary nanocatalysts.

Photocatalytic activity of CdS and Ag2S quantum dots deposited on poly(amidoamine) functionalized carbon nanotubes

Two novel ternary nanocatalysts, f-MWCNTs-CdS and f-MWCNTs-Ag2S were successfully constructed by covalent grafting of fourth generation (G4) hyperbranched, crosslinked poly(amidoamine) (PAMAM) to carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and subsequent deposition of CdS or Ag2S quantum dots (QDs). The structural transformation, surface potential, and morphology of functionalized MWCNTs (f-MWCNTs) and nanocatalysts were characterized by UV–vis spectrophotometer, Fourier transform infrared spectroscopy, powder X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, scanning electron microscopy and energy dispersive spectroscopy. Transmission electron microscopy reveals the effective anchoring of QDs on f-MWCNTs. The catalytic activity of nanocatalysts was evaluated by photodegradation of methyl orange under illumination of UV light. The coupling of MWCNTs, PAMAM and CdS or Ag2S QDs significantly enhanced the catalytic efficiency of nanocatalysts. The rate constants for degradation of methyl orange in presence of nanocatalysts were calculated using the Langmuir–Hinshelwood model. Overall, the excellence in photodegradation was accomplished by hybridizing f-MWCNTs with CdS or Ag2S QDs.