Voltammetric investigation of palladium oxides—I: Their formation/reduction in NaOH

An Alkaline-Acid Glycerol Electrochemical Reformer for Simultaneous Production of Hydrogen and Electricity

This study shows the results, for the first time, of an glycerol alkaline-acid electrolyzer. Such a configuration allows spontaneous operation, producing energy and hydrogen simultaneously as a result of the utilization of the neutralization and fuel chemical energy. The electroreformer—built with a 20 wt% Pd/C anode and cathode, and a Na⁺-pretreated Nafion^® 117—can simultaneously produce hydrogen and electricity in the low current density region, whereas it operates in electrolysis mode at high current densities. In the spontaneous region, the maximum power densities range from 1.23 mW cm⁻² at 30 °C to 11.9 mW cm⁻² at 90 °C, with a concomitant H₂ flux ranging from 0.0545 STP m⁻³ m⁻² h⁻¹ at 30 °C to 0.201 STP m⁻³ m⁻² h⁻¹ at 90 °C, due to the beneficial effect of the temperature on the performance. Furthermore, over a chronoamperometric test, the electroreformer shows a stable performance over 12 h. As a challenge, proton crossover from the cathode to the anode through the cation exchange Nafion^® partially reduces the pH gradient, responsible for the extra electromotive force, thus requiring a less permeable membrane.

Some Aspects on the One-Pot Fabrication of Nanoporous Pd-Au Surface Films by Electrochemical Alloying/Dealloying of (Pd-Au)-Zn from a Chlorozincate Ionic Liquid

The high thermal stability of the Lewis acidic ZnCl₂-1-ethyl-3-methylimidazolium chloride ionic liquid enables the in situ fabrication of hierarchical nanostructured Pd-Au bimetallic surfaces via electrochemical alloying/dealloying of (PdAu)Zn on PdAu substrate in the ionic liquid. Nanostructured PdAu samples that consist of patterned cracks and ligaments are fabricated by using potential cycling method and constant-potential electrolysis method, respectively. The effects of working temperature and amounts of the deposited Zn on the morphology of the dealloyed (PdAu)Zn nanostructure are examined. The formation of the hierarchical nanostructure is a compromise between high-surface-diffusive Au and low-surface-diffusive Pd. Whereas Au in the alloy promotes the nanostructure formation, Pd in the PdAu nanostructure protects this material from coarsening. Compared with the plain PdAu, the nanostructured PdAu surface prepared at 150 °C exhibits a significantly higher active surface area and a high capability for the electro-oxidation of glucose.

Ethanol oxidation on electrocatalysts obtained by spontaneous deposition of palladium onto nickel-zinc materials

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 Pd(IV) salts. 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 Ni--O moieties. As a reference material, a nanostructured Pd/C material was prepared by reduction of an aqueous solution of PdCl(2)/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 microg 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)(-1) at room temperature) and onset potential (as low as -0.6 V vs Ag/AgCl/KCl(sat)).