Early stages of Mg–Nb alloy corrosion in a balanced salt solution – STEM-HAADF and EIS study

Enhanced catalysis of ethylene glycol electro-oxidation (EGO) is reported at a ternary CoOx/NiOx/Pt catalyst in which Pt nanoparticles (nano-Pt), nickel oxide nanoflowers (nanoNiOx), and cobalt oxide nanoparticles (nano-CoOx); are respectively electrodeposited onto a glassy carbon (GC) substrate. The electrocatalytic activity of the catalyst toward EGO depends on the catalyst's composition, loading sequence and loading level besides the electrolyte's pH and temperature. A detailed morphological, compositional, and structural inspection for the catalyst is achieved by FE-SEM, energy dispersive X-ray spectroscopy, and X-ray diffraction, respectively. Cyclic voltammetry is employed to ensure the successful electrodeposition of the catalyst's ingredients and to assess its activity. The superiority of the CoOx/NiOx/Pt/GC catalyst over a series of catalysts employing different ingredients and/or deposition sequence is demonstrated. It supports a larger (ca. fourfold) oxidation peak current, and a significant (ca. -330 mV) negative shift in the onset potential of EGO together with a much more enhanced long-term stability toward continuous electrolysis when compared to the Pt catalyst. The novelty of this investigation extends to employing the electrochemical impedance spectroscopy (EIS) as a probe that provides important information about the reaction pathway of EGO. Interestingly, the maximum capacitance obtained at the CoOx/NiOx/Pt/GC catalyst (coincides with the EGO peak current) is fivefold higher than that obtained at the Pt/GC catalyst at -0.35 V vs. Ag/AgCl. Formic acid and oxalic acid were the major products of EGO, as revealed by high performance liquid chromatography.

Section: Resultsmentioning

confidence: 79%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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EIS-Activity Correlation for the Electro-Oxidation of Ethylene Glycol at Nanoparticles-Based Electrocatalysts

El-Nowihy¹,

Mohammad²,

Sadek³

et al. 2019

“…Those cathodic currents may be attributed to the electrochemical behavior of Co in an alkaline medium, as discussed in Ref. 53 The anodic peaks A0 may be related to the formation of Co oxy/hydroxy compounds in the alkaline medium: 53,54 Co The cathodic currents may corresponded to the reduction of these compounds. 53 The anodic currents that are observed for all catalysts, at potential values larger than 0.6 V, may be attributed to the conversion of Co(II) to Co(III) surface compounds.…”

Section: Resultsmentioning

confidence: 93%

High Performance Direct N₂H₄-H₂O₂ Fuel Cell Using Fiber-Shaped Co Decorated with Pt Crystallites as Anode Electrocatalysts

Zabielaitė

Balčiūnaitė

Šimkūnaitė

et al. 2019

In this study, a fiber-shaped Co coating was electroplated on the Cu surface followed by the deposition of Pt crystallites using the galvanic displacement method. The electrochemical behavior of the prepared Co fiber and Pt nanoparticles decorated Co fiber catalysts were evaluated in order to provide insights into the electro-oxidation of N 2 H 4 in an alkaline media was performed using cyclic voltammetry and chrono-techniques. The influence of Co fiber /Cu and PtCo fiber /Cu as the anode electrocatalyst on the performance of direct N 2 H 4 -H 2 O 2 fuel cell was investigated at different temperatures. The deposition of a small amount of Pt crystallites, in the range of 5 μg Pt cm -2 to 29 μg Pt cm -2 , significantly improved the performance of the fiber-shaped Co catalyst for the electro-oxidation of N 2 H 4 in an alkaline medium. The measured N 2 H 4 oxidation current densities at −0.2 V are approximately 5-6 times larger for different PtCo fiber /Cu catalysts, compared with that of a pure Co fiber /Cu. The single N 2 H 4 -H 2 O 2 fuel cell results showed that the highest peak power density of 219.8 mW cm -2 for the N 2 H 4 -H 2 O 2 fuel cell was obtained with the PtCo fiber /Cu catalyst that has the Pt loading of 28.7 μg Pt cm -2 .

“…However, upon the electrodeposition of CoOx at GNs/GC (Fig. 1, curve b), a broad peak appears in the forward potential scan direction (1.15-1.5 V), 14,[46][47][48][49][50] corresponding to the transformation of CoOx from lower to higher oxidation states ((Co(OH) 2 , Co 3 O 4 , CoOOH, CoO 2 , respectively). Additionally, the reduction of the higher oxidation states of CoOx (CoOOH, CoO 2 ,) to lower oxidation states are disclosed by the broad peak appearing in the backward scan direction within the same potential range.…”

Section: Resultsmentioning

confidence: 99%

Synergistic Effect of Urea on Vitamin C Electro-Oxidation at NiOx/CoOx Binary Catalysts Supported on Graphene Nanosheets

El-Nowihy¹,

El‐Deab²

2022

The electro-oxidation of ascorbate (AAO) in the presence of urea at NiOx/CoOx/GNs/GC electrode is investigated. Cyclic voltammetry measurements show that the peak current (Ip) of AAO at NiOx/CoOx/GNs/GC electrode is ten times that of GNs/GC electrode. This highlights the role of catalyst composition and order of deposition on the activity of AAO. Interestingly, blending ascorbate (AH ̶ ) with urea caused a significant promotion of AAO. Both the Ip of AAO and the fuel utilization in the AH ̶ /urea fuel blend solution are doubled when compared to those obtained at the same electrode in pure AH ̶ solution (in addition to a favorable negative shift in the onset potential, Eonset=150 mV). Urea molecules are believed to act as anchoring molecules for AH ̶ molecules at the NiOx/CoOx/GNs/GC surface with a favorable geometry facilitating its oxidation (by two-electron transfer process) to dehydroascorbate (DHA). Four interaction geometries are proposed, and comparative DFT calculations are conducted, displaying the relative stability and dipole moments of AH ̶ in such a way that facilitates its adsorption and oxidation. These findings demonstrate the crucial role of the catalysts tailoring together with the selection of a smart blending fuel with AH ̶ .