Electrochemical impedance analysis of methanol oxidation on carbon nanotube-supported Pt and Pt-Ru nanoparticles

Acetonitrile’s Effect on the Efficiency of Ethanol Electrooxidation at a Polycrystalline Pt Electrode in Relation to pH-Dependent Fuel Cell Applications

The present paper reports cyclic voltammetric and a.c. impedance spectroscopy investigations on the influence of the acetonitrile concentration on the kinetics (and individual product’s efficiency) of the ethanol oxidation reaction (EOR), performed on a polycrystalline Pt electrode surface in 0.5 M H2SO4 and 0.1 M NaOH supporting solutions. The kinetics of the EOR were examined at room temperature over the voltammetric potential range, which covers the electrooxidation of surface-adsorbed COAds species, as well as the formation of acetaldehyde molecules. In addition, the time-dependent efficiency of acetate and acetaldehyde formation in relation to the initial acetonitrile content for both acidic and alkaline electrolytes was evaluated by means of spectrophotometric Ultraviolet/ Visible Spectroscopy (UV-VIS) instrumental analysis.

In Situ Crystallization of Active NiOOH/CoOOH Heterostructures with Hydroxide Ion Adsorption Sites on Velutipes-like CoSe/NiSe Nanorods as Catalysts for Oxygen Evolution and Cocatalysts for Methanol Oxidation

Hydroxide ion (OH^-) adsorption process is critical for accelerating the half-reactions of both metal-air batteries and direct methanol fuel cells in alkaline media. This study designs a rational catalyst/cocatalyst by constructing the readily available OH^-adsorption sites to boost oxygen evolution reaction (OER) and methanol oxidation reaction (MOR). Cobalt selenide-coated nickel selenide nanorods are in situ grown on nickel foam to obtain CoSe/NiSe-nrs/NF via a one-pot solvothermal synthesis route. CoSe-0.2/NiSe-nrs/NF (Co/Ni molar ratio of 0.26) exhibits an excellent OER activity(an overpotential of 310 mV at 100 mA cm^-2 and a Tafel slope of 58.3 mV dec^-1). The differently oriented CoSe/NiSe-nrs with a velutipes-like structure and metallic property provide a promising electrical conductivity for charge transfer. In situ X-ray diffraction tests verify the crystallization of active β-NiOOH during OER, and the crystallized NiOOH/CoOOH contributes to the excellent OER cycling stability in alkaline media. Synergistic effects between CoSe and NiSe-nrs/NF can balance the formation of NiOOH/CoOOH heterostructures to govern the exposure of available active sites. NiOOH/CoOOH as a highly active component can energetically adsorb OH^- to promote OER. CoSe/NiSe-nrs/NFs as a low Pt-loading (0.5 wt%) support offer the mutually beneficial interactions for promoting cocatalytic and CO_ads (poisonous intermediate) co-oxidation activities toward MOR. The electrochemically active surface area and mass activity of Pt/CoSe-0.2/NiSe-nrs/NF are 85 m² g_pt^-1 and 1437.1 mA mg_pt^-1, respectively, which are much higher than those of commercial Pt/C (10.0 wt%). OH^- absorbed on the NiOOH/CoOOH structure eliminates CO_ads on the Pt surface via bifunctional mechanisms to improve the MOR activity. This study provides a promising reference for designing the versatile catalysts for energy conversion.

Small-sized and highly dispersed Pt nanoparticles loading on graphite nanoplatelets as an effective catalyst for methanol oxidation

A series of high loading Pt nanoparticles (NPs) with a small particle size uniformly dispersed on graphite nanoplatelets (GNPs) have been synthesized in the presence of an imidazolium-based ionic liquid (Pt/I-IL (x)/GNPs). I-IL, an amphoteric ion used as an additive agent to stabilize Pt NPs, can also prevent the aggregation of the GNPs. The results obtained from X-ray diffraction, transmission electron microscopy and electrochemical testing showed that the I-IL assisted synthesis method resulted in size reduction of Pt NPs, an improvement of Pt dispersion on GNPs, and the identification of the relationships between the mean size of Pt NPs and the volume of I-IL. Among all as-prepared Pt/GNP catalysts with or without I-IL assisted, the sample with 10 microliters of I-IL assisted (Pt/I-IL (10)/GNPs) exhibits the highest electrocatalytic activity and the best stability toward the methanol oxidation reaction. Moreover, the Pt/I-IL (10)/GNP catalyst markedly outperforms the commercial Pt/C from Johnson Matthey in terms of both methanol oxidation activity and stability, revealed by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy.