Unmasking the Latent Passivating Roles of Ni(OH)₂ on the Performance of Pd–Ni Electrocatalysts for Alkaline Ethanol Fuel Cells

Abstract

Nicked-based metal−organic framework-derived carbon (Ni/MOFDC) and its acid-treated counterpart (AT-Ni/ MOFDC) have been prepared as supports for palladium nanoparticle electrocatalysts (Pd/Ni/MOFDC and Pd/AT-Ni/MOFDC). These materials have been prepared using facile microwave-assisted techniques. Several spectroscopic and microscopic techniques (such as FTIR, Raman, PXRD, XPS, XANES, FT-EXAFS, and TEM) have been used to thoroughly characterize physicochemical properties of the materials. It is revealed that acid treatment successfully cleaned the metallic Ni surface of the passivating hydroxides (Ni(OH) 2 and NiOOH) to generate a very low concentration of Ni nanoparticles on the carbon support. The Ni-deficient Pd/AT-Ni/MOFDC shows excellent electrocatalytic performance toward ethanol oxidation reaction (EOR) in the alkaline medium compared to the Ni-hydroxide-rich Pd/Ni/MOFDC counterpart.As a proof-of-concept, these electrocatalysts have been employed as anodes and demonstrated for membraneless direct ethanol microfuel cells (μ-DEFCs) with a micro-3D-printed cell, with FeCo/C as electrocatalyst for the oxygen reduction reaction at the cathode. The Pd/AT-Ni/MOFDC displays increased peak power density (P m = 26.49 mW cm −2 ) with 68% voltage retention after a 24 h galvanostatic discharge test at 40 mA cm −2 and reduced impedance. The improved electrocatalytic properties of the Pd/AT-Ni/MOFDC underscore the need to clean the nickel surface of its passivating hydroxides to harness its full promotional activities toward alcohol oxidation reaction on precious metal electrocatalysts.

Bifunctional Behavior of Pd/Ni Nanocatalysts on MOF‐Derived Carbons for Alkaline Water‐splitting

“…The last EIS parameter in the Voigt EEC model is constant phase element ( CPE ), although it is not significant for the OER kinetics, indicates the non‐ideal capacitive behavior of the nanocatalysts during the OER. This behavior was corroborated with the ideality factor (0.5<a<1), showing deviation from the ideal double‐layer capacitance ( C dl ), according the Z CPE impedance power law [69].…”

Experimental and Theoretical Studies on the Protective Effect of a Biomass Corrosion Inhibitor (vigna radiata) on Mild Steel in Acidic Medium

“…The circuit model shown comprises of a single CPE and charge transfer resistance elements which denote the impedance effect as a result of corrosion product species for the uninhibited environment. In this circuit, the CPE was used as a replacement for pure capacitance to recompense for the electrode surface unevenness frequently initiated by the buildup of corrosion products and lack of uniformity of the metal surfaces [29, 30] including surface micro‐defects.…”

“…To estimate the obtained values of the corresponding impedance parameters shown in Table 2, the resultant spectra were evaluated with the aid of an equivalent circuit employed to model the metal/acid interface [6, 29]. The diameter of the convectional arc of the impedance is associated to the charge transfer resistance (R ct ).…”

“…Four active constituents mentioned earlier were selected for computational modeling. Molecular dynamics simulations were employed to sample diverse low energy adsorption conformations of each molecule on the Fe surface [29, 50]. The Fe slab for the simulations was cleaved along the (110) plane.…”

Palladium/Stannic Oxide Interfacial Chemistry Promotes Hydrogen Oxidation Reactions in Alkaline Medium

“…[16,17] One of the strategies to make MOFs useful in electrocatalysis is to subject them to carbonization and chemical etching, wherein the MOFs are used as sacrificial templates to prepare novel carbon materials as electrocatalysts and/or catalyst supports with inherent properties for different applications. [18][19][20][21][22] However, to the best of our knowledge, there has been no report on the use of Pd-based electrocatalysts supported on MOFs-derived carbons for the alkaline HOR. Modification of nanostructured Pd with the cocatalysts like Ag, Sn, Ni, Cu improves the electrocatalytic performance of the Pdbased electrocatalysts.…”