In the present work, the hydrotalcite-like materials known as layered double hydroxides (LDHs) were synthesized. The Ni–Al and Ni–Fe materials with different Ni/Fe ratio were obtained by coprecipitation method at variable pH. The LDH structure was verified by X-ray diffraction, Fourier transform infrared, and Raman spectroscopy. No secondary extra phases were observed for any material. The electronic properties were evaluated by UV–vis spectroscopy, while the magnetic ones were followed by electron paramagnetic resonance (EPR). The results suggested that sample H/Ni–Fe2 (Ni/Fe = 2) has a ferrimagnetic behavior as a result of the combined action of NiII–OH–NiII, FeIII–OH–NiII, and FeIII–OH–FeIII pairs across the layers and ferromagnetic interactions operating between layers. Furthermore, the material H/Ni–Fe1 (Ni/Fe = 1.5) showed a combination of paramagnetic and ferromagnetic interactions which favors a superexchange interaction among metal centers through the OH bridges across the cationic sheets; the superexchange interaction enhances the electrocatalytic activity on the oxygen evolution reaction (OER) in alkaline media. On the other hand, XPS experiments showed that the H/Ni–Fe1 did not exhibit structural changes after electrochemical processes. The activity toward the OER was in the order H/Ni–Fe1 > H/Ni–Fe2 > H/Ni–Al, as was confirmed using in situ linear sweep voltammetry (LSV) coupled with mass spectrometry (differential electrochemical mass spectrometry).

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In this work, platinum nanoparticles were impregnated by two different techniques, namely the carbonyl chemical route and photodeposition, onto systematically surface-modified multiwalled carbon nanotubes. The different interactions between platinum nanoparticles with sp(2)-sp(3) carbon nanodomains were investigated. The oxidation of an adsorbed monolayer of carbon monoxide, used to probe electronic catalytic modification, suggests a selective nucleation of platinum nanoparticles onto sp(2) carbon nanodomains when photodeposition synthesis is carried out. XPS attests the catalytic center electronic modification obtained by photodeposition. DFT calculations were used to determine the interaction energy of a Pt cluster with sp(2) and sp(3) carbon surfaces as well as with oxidized ones. The interaction energy and electronic structure of the platinum cluster presents dramatic changes as a function of the support surface chemistry, which also modifies its catalytic properties evaluated by the interaction with CO. The interaction energy was calculated to be 8-fold higher on sp(3) and oxidized surfaces in comparison to sp(2) domains. Accelerated Stability Test (AST) was applied only on the electronic-modified materials to evaluate the active phase degradation and their activity toward oxygen reduction reaction (ORR). The stability of photodeposited materials is correlated with the surface chemical nature of supports indicating that platinum nanoparticles supported onto multiwalled carbon nanotubes with the highest sp(2) character show the higher stability and activity toward ORR.

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This work revises the essentials of electrocatalytic electrochemical measurement done in alkaline electrolytes. The hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) were considered as a baseline to understand some key critical factors in a half-cell system. The material considered herein was essentially the carbon supported platinum nanoparticles as benchmark material. The main electrochemical techniques considered were cyclic voltammetry (CV) and the rotating disk electrode (RDE). The critical factors considered were the electrochemical cell vessel, reference electrode, nature of the cation in the alkaline electrolyte, and ohmic drop correction. The anion-exchange membrane as electrolyte for alkaline fuel cells (AFCs) provides opportunities to develop non-precious metal (NPM) catalytic centers. This is certainly an advantage that AFC can offer to activate NPM toward the cathodic oxygen reduction reaction (ORR), with a performance approaching that of platinum (Pt). Nonetheless, in such an alkaline medium the hydrogen oxidation reaction (HOR) is challenging, even for platinum that shows a sluggish kinetics and regardless of the fact the mechanism is still not well-understood.2 Numerous efforts to tailor high active and stable nanostructured electrocatalyst (including precious and non-precious centers) for AFCs have been performed. Moreover, important experimental issues have not yet being normalized. This is essential, in order to compare data generated in various laboratories. A series of experimental questions, such as, ink formulation, thin-film coated quality, catalyst loading, electrochemical cell, reference electrode, temperature, electrolyte cation and so on, can indeed affect considerably the electrochemical measurements. One can, moreover, find in the literature excellent protocols to normalize fuel cell electrocatalytic reactions in acid measurements, 3-7 using commercial Pt/C as benchmark material. Protocols for the alkaline medium are seldom, however, a recent work analyses the impact of impurities in alkaline electrolytes. 8 Moreover, to the best of our knowledge, the reported data to obtain reproducible and comparable results in alkaline media are still lacking, since different experimental protocols used for the evaluation of, e.g., benchmark Pt/C in alkaline medium, make it difficult to compare the HOR, and ORR kinetics. Reproducibility and replicability in the measurements is of paramount importance in order to assess good performance of advanced electrocatalytic materials. This work provides a protocol to perform, as a baseline, the HOR and ORR processes, generated on carbon supported platinum NPs in alkaline electrolyte. An Overview on Alkaline HOR and ORR Data in the Last DecadeThe research on fuel cell reactions (HOR and ORR) in alkaline medium reflects the principal development of the proton-exchange membrane fuel cells (PEMFC). The former approach is more focused on novel NPM catalytic centers. Commercial-based platinum electrocatalytic material in massif, single cr...