Enhanced electrocatalytic effects of Pd particles immobilized on GC surface on the nitrite oxidation reactions (original) (raw)
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Electrochemical oxidation of ethanol on palladium-nickel nanocatalyst in alkaline media
2016
Pd-Ni/C catalyst was synthesized employing a borohydride reduction method. The high area Ni was first dispersed on the carbon support and then modified by Pd nanoparticles. Transmission electron microscopy confirmed relatively even distribution of Ni across the carbon support with discrete pal-ladium particles of about 3.3 nm mean diameter on it. Cyclic voltammetry confirmed the presence of Ni on the catalyst surface. The activity of the Pd-Ni/C catalysts for ethanol oxidation reaction (EOR) in alkaline solution was tested under the potentiodynamic and potentiostatic conditions and the results were compared to those obtained on the Pd/C catalyst. It was found that Pd-Ni/C is more active for the EOR compared to Pd/C by a factor up to 3, depending on the type of experiments and whether specific activity or mass activity are considered. During the potentiodynamic stability test an interesting phenomenon of activation of Pd-Ni/C catalyst was observed. It was found that maximum activity is attained after fifty cycles with the positive potential limit of 1.2 V, regardless of whether they were performed in the electrolyte with or without ethanol. It was postulated that potential cycling of the Pd-Ni surface causes reorganization of the catalyst surface bringing Pd and Ni sites to a more suitable arrangement for the efficient ethanol oxidation.
2009
Binary and ternary composite films of Pd, multiwalled carbon nanotubes (MWCNTs) and Ni are obtained on glassy carbon electrodes and investigated as electrocatalysts for the ethanol oxidation reaction in alkaline medium. The steady-state anodic Tafel polarization study shows that small introduction (1-5%) of MWCNTs to Pd increases the apparent electrocatalytic activity greatly, the magnitude of enhancement, however, being the greatest ($26 times) with 1%MWCNT. Addition of 1%Ni to the active Pd-1%MWCNT composite improved the apparent electrocatalytic activity (over 50%) further, but its higher additions (2-5%)
Pd, Ni and Pd–Ni nanoparticles uniformly dispersed on Vulcan XC-72R carbon black are prepared by microwave-irradiation using NaBH4 as a reducing agent. Pd/C, Ni/C and Pd–Ni/C electrocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). Pd–Ni alloy was formed with an average particle size of 3 nm. Kinetic parameters such as the electron transfer coefficient value (˛) and electron transfer rate constant of Ni/C and Pd–Ni/C electrocatalysts in 0.5 M KOH solution were calculated. The prepared electrocatalysts were examined for methanol oxidation in alkaline medium. The long-term stability of electrocatalysts in (0.6 M MeOH + 0.5 M KOH) solution was studied using repeated cyclic voltammetry and chronoamperometry. Two methanol oxidation peaks were observed at Pd–Ni/C at 0 and +913 mV. Their current density values are higher than those at Pd/C and Ni/C electrocatalysts by 3.84 and 1.43 times, respectively. The catalytic rate constant at Ni/C and Pd–Ni/C was estimated using double-step chronoamperometry as 1.80 × 103 and 5.88 × 103 cm3 mol−1 s−1, respectively. Pd–Ni/C showed better stability performance when compared to Pd/C and Ni/C electrocatalysts.
Fullerenes, Nanotubes and Carbon Nanostructures, 2018
In this work, Pd-Ni and Pd nanoparticles are deposited on Vulcan carbon (XC-72R), multi-walled carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO) and investigated towards oxygen reduction reaction (ORR). The structural features of catalyst are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). The ORR activity of catalysts is investigated via cyclic voltammetry (CV), rotating disk electrode (RDE), electrochemical impedance spectroscopy (EIS) and chronoamperometry techniques. Comparative CV analysis reveals higher electrochemical active surface area (ECSA) of Pd-Ni/rGO catalyst. This result suggests a general approach of a synergistic effect between Pd and Ni nanoparticles and better Pd-Ni dispersion on graphene sheets. The results from ORR measurements show that Pd-Ni/rGO has remarkable electrocatalytic activity and stability compared to Pd/C. The Koutecky-Levich and Tafel analysis suggest that the proposed main path in the ORR mechanism is direct four-electron transfer process with faster transfer kinetic rate on the Pd-Ni/rGO.
Journal of Electroanalytical Chemistry, 2019
Electrochemical deposition by applying potential steps between −0.25 (or 0 V) and 0.85 V (vs SCE) was used to deposit Pd on different nanocarbon substrates. Influence of overpotential on the electrodeposition process was observed. Obtained Pd/C catalysts were studied with scanning electron microscopy and electrochemically in alkaline solution. Specific activity for the oxygen reduction reaction (ORR) of the catalysts was determined using the rotating disc electrode method. The ORR on all the studied Pd/C catalysts proceeded through a 4-electron pathway with a rate-limiting step of the first electron transfer to the O 2 molecule. Pd catalysts deposited on graphene nanosheets showed highest specific activities for the ORR. The prepared catalysts showed higher specific activities than commercial Pd/C catalysts, which can be due to electrodeposition process proceeding without the presence of intrusive additives used in chemical synthesis of nanoparticles. Electrochemical activation was employed to improve the electrocatalytic activity of carbon nanotube-supported Pd catalysts for ORR. Au(111) upon immersion of Au(111) electrode into H 2 PtCl 4 solution at OCP [8]. Same group conducted similar experiment with Pd showing that the adsorption of Pd species on Au(111) was similar to that of Pt, furthermore while studying the deposition of Pd they noticed that the adsorption of PdCl 4 2− ions inhibited 3D growth [9,10]. Pd electrodeposition on different Au(hkl) facets was studied by Kibler and coworkers and it was shown that Pd preferably grows on Au defects [11-13]. In their further work they pointed out changes in deposition process when moving from chloride solution to sulphuric acid solution, showing that the growth of Pd in chloride-free solution favours 3D growth mode [14]. Contradicting evidence was found by Wang et al. showing that chlorides did not inhibit 3D growth [15]. Similar deposition mechanisms have also been noted on some carbon materials studied by different groups: glassy carbon (GC) [16-21], carbon black [22-25], carbon paper [26-28], single-walled carbon nanotube [29], multi-walled carbon nanotube (MWCNT)
Chemsuschem, 2009
Ni-Zn and Ni-Zn-P alloys supported on Vulcan XC-72 are effective materials for the spontaneous deposition of palladium through redox transmetalation with PdIVsalts. The materials obtained, Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C, have been characterized by a variety of techniques. The analytical and spectroscopic data show that the surface of Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C contain very small, highly dispersed, and highly crystalline palladium clusters as well as single palladium sites, likely stabilized by interaction with oxygen atoms from NiO moieties. As a reference material, a nanostructured Pd/C material was prepared by reduction of an aqueous solution of PdCl2/HCl with ethylene glycol in the presence of Vulcan XC-72. In Pd/C, the Pd particles are larger, less dispersed, and much less crystalline. Glassy carbon electrodes coated with the Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C materials, containing very low Pd loadings (22–25 μg cm−2), were studied for the oxidation of ethanol in alkaline media in half cells and provided excellent results in terms of both specific current (as high as 3600 A g(Pd)−1at room temperature) and onset potential (as low as −0.6 V vs Ag/AgCl/KClsat).
Enhanced performance of nano-electrocatalysts of Pd and PdCo in neutral and alkaline media
Journal of Applied Electrochemistry, 2018
Pd and PdCo nanostructures are synthesized by a soft-template route to be applied as electrocatalysts. Distinctive morphologies are obtained: nanowire-like structures, with mean diameter d = 33 nm (Pd NW), forming an entangled network; nanocubes (Pd NC) 64 nm in side, and PdCo (NS) nanospheres 60 nm in diameter. Pd:Co feed mol ratios (2:1) and (5:1) are used. Pd and Pd-Co nanostructures both crystallize in an fcc structure. A glassy carbon (GC) electrode is then modified with these colloidal dispersions, and further characterized by electrochemical methods. The modified Pd NW /GC, Pd NC /GC, and PdCo NS / GC electrodes are applied in the oxygen reduction (ORR) and oxygen evolution (OER) reactions, in a phosphate buffer pH 7 and 0.1 M NaOH solution. Voltammetric measurements are consistent with a diffusion-controlled mechanism, with a four-electron reduction process in each Pd and PdCo nanoelectrode. Resulting values of kinetic parameters indicate that the relative effectiveness of these solutions in ORR may be ordered as PdCo (5:1) NS /GC ≥ PdCo (2:1) NS /GC > Pd NC /GC ≥ Pd NW / GC > GC. For the OER, Tafel slopes are measured for the nanosized electrodes in both types of supporting electrolytes. Turnover frequencies estimated in alkaline solution for the OER indicate that nanostructured bimetallic PdCo NS /GC electrodes exhibit better activity than Pd/GC ones.
Enhanced Activity and Selectivity of Carbon Nanofiber Supported Pd Catalysts for Nitrite Reduction
Environmental Science & Technology, 2012
Pd-based catalyst treatment represents an emerging technology that shows promise to remove nitrate and nitrite from drinking water. In this work we use vaporgrown carbon nanofiber (CNF) supports in order to explore the effects of Pd nanoparticle size and interior versus exterior loading on nitrite reduction activity and selectivity (i.e., dinitrogen over ammonia production). Results show that nitrite reduction activity increases by 3.1-fold and selectivity decreases by 8.0fold, with decreasing Pd nanoparticle size from 1.4 to 9.6 nm. Both activity and selectivity are not significantly influenced by Pd interior versus exterior CNF loading. Consequently, turnover frequencies (TOFs) among all CNF catalysts are similar, suggesting nitrite reduction is not sensitive to Pd location on CNFs nor Pd structure. CNF-based catalysts compare favorably to conventional Pd catalysts (i.e., Pd on activated carbon or alumina) with respect to nitrite reduction activity and selectivity, and they maintain activity over multiple reduction cycles. Hence, our results suggest new insights that an optimum Pd nanoparticle size on CNFs balances faster kinetics with lower ammonia production, that catalysts can be tailored at the nanoscale to improve catalytic performance for nitrite, and that CNFs hold promise as highly effective catalyst supports in drinking water treatment.