Comprehensive Characterization of Nickel-Based Metallic Foams and Their Applications as Electrocatalyst Materials
Van Drunen, Julia
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This contribution explores the applicability of nickel-based metallic foams as active electrodes and as electrocatalyst support materials. A comprehensive characterization of Ni and multi-component Ni-based foams is presented and includes the analysis of their structural, chemical, and electrochemical properties. Several materials and surface science techniques as well as electrochemical methods are used to examine the structural characteristics, surface morphology, and surface-chemical composition of these materials. X-ray photoelectron spectroscopy is employed to analyze the surface and near-surface chemical composition. The specific and electrochemically active surface areas (As, Aecsa) are determined using cyclic voltammetry (CV). The foams exhibit structural robustness typical of bulk materials and they have large As, in the 200 – 600 cm2 g–1 range. In addition, they are dual-porosity materials and possess both macro and meso pores. Nickel foam electrodes are applied as electrocatalysts for the oxidation of isopropanol. The process is studied under well-defined experimental conditions using cyclic voltammetry. The outcome of these experiments demonstrates that isopropanol oxidation requires the presence of -NiOOH on the Ni foam electrode. This surface oxide is generated at potentials near the potential of the isopropanol oxidation; however, the two processes do not occur exactly at the same potentials. The Ni foam anodes sustain a current density of ca. 2.6 mA cm–2 throughout an electrolysis time of up to 600 minutes without significant loss of electrocatalytic activity. Isopropanol is converted to acetone at a rate of ca. 5.6 mM per hour. The applicability of Ni foams as support materials for Pt is investigated. Platinum particles are deposited on Ni foam in low loading amounts via the chemical reduction of Pt2+ and Pt4+ originating from aqueous Pt salt solutions. The resulting Pt / Ni foams are characterized using electrochemical, analytical, and materials analysis techniques, including SEM to examine the morphology of the deposited material, CV to evaluate the Aecsa of the deposited Pt, and inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the mass of deposited Pt. The Pt / Ni foams are applied as electrocatalysts for hydrogen evolution, hydrogen reduction, oxygen evolution, and oxygen reduction reactions in alkaline electrolyte.