A Comparative Study on Gold and Platinum Dissolution in Acidic and Alkaline Media

Abstract

Electrochemical dissolution of gold and platinum in 0.1 M HClO 4 , 0.1 M H 2 SO 4 , and 0.05 M NaOH is investigated. The qualitative picture of both metals' dissolution is pH-independent. Oxidation/reduction of the metal's surface leads to the transient dissolution peaks which we label A 1 and C 1 on the dissolution profiles. Commencement of the oxygen evolution reaction (OER) results in the additional dissolution peak A 2 . Quantitatively, there are important differences. The amount of gold transiently dissolved in alkaline medium is more than an order of magnitude higher in comparison to that in acidic medium. Oppositely, steady-state gold dissolution in base in the potential region of OER is hindered. The transient dissolution of platinum is by a factor of two higher in base. It is suggested that variation of the pH does not change the mechanism of the OER on platinum. Consequently, the dissolution rate of platinum is equal in acidic and alkaline electrolytes. As an explanation of the observed difference in gold dissolution, a difference in the thickness of compact oxide formed in acid and base is suggested. Growth of a thicker compact oxide in the alkaline medium explains the increased transient and the decreased steady-state dissolution of gold. Platinum and gold are perhaps the most frequently studied metals in electrochemistry. In particular, they constitute important model systems in the context of fundamental investigations of the mechanism and kinetics of the initial stages of metal oxidation. Surface processes during transition of adsorbed hydroxyl groups to, initially, compact couple of monolayers thickness and, later, relatively thick bulk phase oxides have occupied electrochemists for many decades. In the earliest works, investigations were directed toward the general problem of metal passivity, hotly debated at the beginning of the twentieth century. [1][2][3] In the 1960s and 1970s, the rapid development of fuel cells and application of platinum as a catalyst for the hydrogen oxidation and the oxygen reduction reactions (HOR and ORR) re-stimulated research efforts on noble metal oxidation. As adsorbed intermediates and other oxygenated species present on the catalyst surface were believed to have a poisoning effect on the rate of the ORR, understanding of the oxygen-platinum interaction was of substantial importance. The great progress in the development of electrochemical experimental techniques and surface analytics in these years significantly contributed to new insights of electrocatalysis at the solid-liquid interface. The understanding of noble metal oxidation is, however, not only crucial for these reactions but also the essential step in the comprehension of dissolution. Despite its importance in general and as a basis for the current work, the description of the theories and models for noble metal oxidation over the last century is beyond the scope of the present article. The interested reader is therefore referred to a comprehensive work published by Conway, and references therein. Plat...

Dissolution of Platinum in the Operational Range of Fuel Cells

“…[11] One particular finding in the on-line ICP-MS studies was that the onset potentialo fp latinum anodic dissolution in at ransientexperiment (depending on the electrolyte, values of 1.0-1.1 V RHE were found, asc an be seen in Table 1i nR ef. [12]) coincides well with the initiation of platinum bulk oxidation, usually ascribed to an interfacialp lace-exchange process at approximately 1.1-1.2 V RHE . [13] The appearance of platinum in the electrolyte during cathodic treatment was correlatedw ith oxide reduction and, thus, with the reverseo ft he oxidation process.…”

“…As an example, in previous simple potential cycles to 1.05 V RHE , platinum dissolution was found to be negligibly small, [12] whereas as ignificant amount of platinum is found in the electrolytea fter polarization, even at lower potentials over 30 min. To demonstrate this time dependence for the current system, Figure 3p resents the dependence of anodic and cathodic dissolution on the anodization time for nanoparticles and bulk platinum electrodes.…”

“…For the sake of clarity,t he segment of the mass spectrumcorresponding to platinum dissolution during the activation treatment (as for instance in Fig-ure 5b in Ref. [12]) is omitted. Prior to the polarization step, the electrode was held at ap otentialo f0 .4 V RHE ,a tw hich dissolutiono fm etallic platinum in oxygen-free electrolyte is assumed to be negligibly small.…”

“…[12]), this results in 200 cycles for dissolution of af ull monolayer or,i no therw ords, the dissolution of four atoms from an anoparticle in one cycle. It is expected that the dissolution processa tl ow potential is accelerateda tt he higher temperatures at whichP EMFCsu sually operate.…”

Ambient-Pressure XPS Study of a Ni–Fe Electrocatalyst for the Oxygen Evolution Reaction

“…We note that the observed spectral change is within a potential region where Au electrodes undergo surface oxide formation. 27,28 However, if Au oxidation took place, we would expect the Au 4f spectra to exhibit a new component at ~1 eV higher binding energy; such a spectral change was not detected in our measurements ( Figure S7). The additional oxide species appears at a potential at which, according to the cyclic voltammogram, we do not yet expect oxidation of Ni(OH) 2 to NiOOH.…”