Influence of Nanocrystalline Palladium Morphology on Alkaline Oxygen Reduction Kinetics

Abstract

The structure sensitivity of the alkaline oxygen reduction reaction (ORR) on palladium is of great interest as cost considerations drive the need to find a replacement for platinum catalysts. The kinetics of alkaline ORR were investigated on nanocrystalline palladium (Pd) films with domain sizes between 14 and 30 nm that were synthesized by electrodeposition from aqueous electrolytes. Ten Pd films were prepared under varying electrodeposition parameters leading to each having a unique texture and morphology. The sensitivity of initial alkaline ORR kinetics to the Pd surface structure was evaluated by measuring the kinetic current density and number of electrons transferred for each film. We show through scanning electron microscopy (SEM), x-ray diffraction (XRD), atomic force microscopy (AFM), and voltammetry from rotating disc electrodes (RDEs) that the fastest alkaline ORR kinetics are found on Pd surfaces with high surface roughness, which themselves are composed of fine grains. Such a study is useful for developing membrane electrode assemblies (MEAs) based on directly electrodepositing catalyst onto a conductive diffusion layer.

Heterogeneous NiO2-to-Pd Epitaxial Structure Performs Outstanding Oxygen Reduction Reaction Activity

“…Although, Pd-based NCs have great potential to be a cheaper alternative, a gap in catalytic performance (in terms of both activity and stability) between Pd and Pt still exists. To fill the gap, lots of strategies have been proposed, including alloying with cheap transition metals, controlling the morphology or architecture, − atomic vacancies, tuning the particle size, coupling with optimized support materials, and so on but in vain. Core–shell structured NCs with Pd as an active shell and low electronegativity transition metal in the core show high activity in ORR.…”

Membrane-Less Ethanol Electrooxidation over Pd-M (M: Sn, Mo and Re) Bimetallic Catalysts

“…As shown in Figure 5, 20% Pd 50 Sn 50 /C was significantly more stable than Pd 50 Re 50 /C, which showed a continuous increase in voltage with time. This behavior has been previously ascribed to intermediate species remaining adsorbed on the catalyst surface, increasing the anodic polarization resistance as a result [6,43,46]. Open circuit conditions allowed these intermediates to desorb, recovering the initial voltage values.…”

“…The electrochemical surface area of the catalysts (ECSA, Table 1) was calculated from the CV curves in Figure 2, considering the area under the large reduction current of PdO (peak IV) [14,29,42,43]. These ECSA values were obtained as follows:…”

Oxygen reduction reaction on Pd nanocatalysts prepared by plasma-assisted synthesis on different carbon nanomaterials

“…In order to reduce the noble metal loading in the catalyst material, well dispersed small Pd particles must be used. Two predominant methods to prepare nanoparticulate Pd catalysts on a carbon support are electrodeposition [4][5][6][7][8][9][10][11] and chemical reduction of Pd salts [12]. Generally, chemical synthesis methods require surfactant additives in order to achieve a good dispersion, suppressing the agglomeration of the particles and their growth.…”