No abstract

No abstract

Pd and PdM (M = Fe and Co) nanostructured electrocatalysts were synthesized by the impregnation method and supported on carbon black Vulcan XC-72R for the formic acid oxidation reaction, FAOR, in acid medium. Nitrates or chlorides were used as Fe and Co precursors to study the counter ion role on the physicochemical features and electrochemical performance of the electrocatalysts. TEM analysis showed that PdM was deposited on the carbon material with a particle size around 2-3 nm. From XRD, peaks associated with the fcc palladium planes were observed along with evidence of PdM alloy formation, particularly when the nitrate salts were used as metal precursors. Furthermore, XPS analyses indicated that nitrates promote the metal oxide formation to a greater extent than chlorides, mainly for Pd.PdCo electrocatalyst obtained from nitrates exhibited the highest performance for FAOR with a steady state current density of 451 and 313 µA cm -2 at 200 and 400 mV respectively, which is in both cases, 3 times larger than that developed for a commercial Pd/C catalyst.

From potentiodynamic and potentiostatic electrochemical methods it was assessed, for the first time, the kinetics and mechanism involved during the electrochemical synthesis of palladium nanoparticles, PdNPs, from a deep eutectic solvent, DES, formed by the choline chloride and ethylene glycol eutectic mixture at 298 K. It was found that the potentiostatically electrodeposited PdNPs were formed through multiple 3D nucleation with diffusion-controlled growth. The nucleation frequency and the nucleation active sites increased linearly and exponentially with applied potential, respectively, and the Pd(II) ions diffusion coefficient, D, in DES was D = (2.77 ± 0.19) 10 −7 cm 2 s −1 . The morphology and composition of the PdNPs were characterized by SEM and XPS, respectively. The PdNPs were homogeneously dispersed onto the GCE surface, with monodispersed size ((41 ± 5) nm) and were formed mainly by metallic palladium with small amounts of PdO and PdO 2 . Furthermore, it was also shown that the GCE-PdNPs modified electrode depicts a high catalytic activity toward formic acid electrochemical oxidation reaction, revealing a mass activity of (4200 ± 100) mA mg Pd −1 at the peak potential, much greater than those reported so far for other PdNPs synthesized by means of sophisticated, time-consuming methods.

In this work, the leaching of the active material electrodes of spent alkaline batteries was carried out using a deep eutectic solvent formed by acetylcholine chloride-urea as leaching medium. From the leaching liquors of the cathode or the cathode/anode mix, the electrochemical formation of Mn or Mn-Zn alloy, onto a glassy carbon electrode, was respectively performed by means of cyclic voltammetry and chronoamperometry techniques. The analysis of the potentiostatic current density transients was done using of models that involve the three-dimensional nucleation and diffusion controlled growth of a) bimetallic phases [Díaz-Morales et al. J. Solid. State Electrochem. 17 (2013) 345–351], in the case of the Mn-Zn alloy and b) metallic nuclei, for Mn electrodeposition [Scharifker and Mostany, J. Electroanal. Chem., 177 (1984) 13–23]. From scanning electron microscopy and EDX, it was verified that the nuclei formed were composed of Mn, or the Mn-Zn alloy depending on the leaching liquors used.