Palladium electrodissolution from model surfaces and nanoparticles

Abstract

Palladium (Pd) is considered as a possible candidate as catalyst for proton exchange membrane fuel cells (PEMFCs) due to its high activity and affordable price compared to platinum (Pt). However, the stability of Pd is known to be limited, yet still not fully understood. In this work, Pd dissolution is studied in acidic media using an online inductively coupled plasma mass spectrometry (ICP-MS) in combination with an electrochemical scanning flow cell (SFC). Crucial parameters influencing dissolution like potential scan rate, upper potential limit (UPL) and electrolyte composition are studied on a bulk polycrystalline Pd (poly -Pd). Furthermore, a comparison with a supported high -surface area catalyst is carried out for its potential use in industrial applications. For this aim, a carbon supported Pd nanocatalyst (Pd/C) is synthesized and its performance is compared with that of bulk poly -Pd. Our results evidence that the transient dissolution is promoted by three main contributions (one anodic and two cathodic). At potentials below 1.5 VRHE the anodic dissolution is the dominating mechanism, whereas at higher potentials the cathodic mechanisms prevail. On the basis of the obtained results, a model is thereafter proposed to explain the transient Pd dissolution.(C) 2017 Elsevier Ltd. All rights reserved

Monometallic Palladium for Oxygen Reduction in PEM Fuel Cells: Particle-Size Effect, Reaction Mechanism, and Voltage Cycling Stability

“…8 In a third approach, the Pd ECSA could be obtained from averaging the H-upd charge (i.e., taking the average between the areas i and ii indicated in Figure 1b), which is described by H + + e − + Pd * ↔ PdH ads [4] and where Pd * denotes an unoccupied Pd surface site. However, the Pd ECSA probed by this method will likely be underestimated in the practically relevant case where the negative integration limit is restricted to 0.10 V RHE in order to minimize contributions from hydrogen absorbed into the Pd bulk structure (H abs ): 9 PdH ads ↔ H abs + Pd * [5] A more detailed description of the interplay of these reactions (Equations 4 and 5) was given by Breger and Gileadi., 29 and by Siebel et al 9 Due to an equilibrium of adsorbed and absorbed hydrogen, Pd * sites available for the adsorption of additional hydrogen are recycled, and, consequently, the measured H-upd charge can increase above its monolayer limit in the case where substantial amounts of H can be absorbed. However, at ≥0.1 V RHE the equilibrium H 2 pressure is too low to allow the formation of the Pd hydride β-phase (PdH ≈0.6 ), and only very low concentrations of dissolved hydrogen (the so-called α-phase) can be formed.…”

Electrochemical On‐line ICP‐MS in Electrocatalysis Research

“…Concerning dissolution mechanism of Pd, more defined systems have to be considered first. Thus, a comparative study on dissolution of polycrystalline Pd and Pd/C at identical experimental conditions was recently performed . It was shown that while the extent of dissolution is different, which may be related to the differences in mass transfer, the same dissolution mechanism is operative for both electrodes.…”

Addressing stability challenges of using bimetallic electrocatalysts: the case of gold–palladium nanoalloys

“…7,55 As already observed for polycrystalline material, the Pd dissolution per cycle (≈117 ng cm −2 ) is more extensive than those of gold and other noble metals. 56,65 Moreover, instead of two separate peaks resulting from oxidation and reduction, the presence of a third and sometimes fourth peak indicates that additional processes, recently clarified, 56 play an important role. These can be related to the complex structure of Pd oxides, the oxidation state of Pd and the chemical composition of the oxide.…”

“…The development of a unique experimental technique that combines online inductively coupled plasma mass spectrometry (ICP-MS) with an analytics electrochemical scanning flow cell (SFC) 52,53 has permitted the timeresolved quantification of low amounts of dissolved elements during catalytic studies, and thus significantly contributed to fundamental understanding of dissolution/degradation processes, like the dissolution of bulk (foil or disk) noble metals, 54 including different studies on gold 7,55 and palladium. 56 While polycrystalline bulk materials constitute model systems for understanding the fundamental dissolution mechanisms, the stability of real-application high surface area catalysts has not been comprehensively investigated. 57 Furthermore, due to the complexity of the alloy interface, the number of studies on bimetallic nanoparticle dissolution is limited.…”