Influence of the Working and Counter Electrode Surface Area Ratios on the Dissolution of Platinum under Electrochemical Conditions

Abstract

The potential variation of Pt counter electrode (CE) in a three-electrode configuration is monitored as the potential of Pt working electrode (E WE ) follows a triangleshaped program in 0.5 M aqueous H 2 SO 4 . The spontaneously adopted CE potential (E CE ) is reported for different values of the ratio of geometric surface areas of WE and CE (A geom,WE /A geom,CE ). The E CE versus time (t) transients are non-linear and resemble charging/discharging curves. In the case of A geom,WE > A geom,CE , E CE adopts higher values than E WE , and vice versa. In the case of A geom,WE /A geom,CE = 10:1, the values of E CE are 0.3 -0.4 V higher than the highest values of E WE . The high E CE values give rise to the development of a thick surface oxide that undergoes subsequent dissolution. A novel three-compartment electrochemical cell is employed to examine simultaneously the dissolution of WE and CE, andto monitor their potentials; the amount of dissolved Pt is quantitatively analyzed using inductively coupled plasma mass spectrometry. The magnitude of the A geom,WE /A geom,CE ratio has a significant impact on the CE oxidation and dissolution. The oxidation and dissolution of CE depend on the lower potential limit of WE; the amount of surface oxide and the quantity of dissolved Pt significantly increase as the WE potential limit is reduced from 0.50 V to 0.05 V because CE adopts a high potential. The presence of dissolved O 2 also affects the dissolution of CE but to a lesser extent than the A geom,WE /A geom,CE ratio or the lower potential limit of WE. Field emission scanning electron microscopy analysis of the CE morphology following prolonged potential cycling in the presence of dissolved O 2 reveals a thick surface oxide that has dry mudlike structure. The slightly higher dissolution of CE under these conditions is attributed to physical detachment of some of the cracked surface oxide. This research advances the understanding of Pt dissolution with some of the new knowledge being applicable to fuel cells.

From Bad Electrochemical Practices to an Environmental and Waste Reducing Approach for the Generation of Active Hydrogen Evolving Electrodes

“…We claim herein that platinum oxide species formed on the Pt anode may be dissolved in the H 2 SO 4 and cationic Pt oxide species can be electrodeposited on the Ni42 steel (Figure f). This assumption seems to be founded for example, Mitsushima et al . investigated the dissolution of Pt in the presence of O 2 in sulfuric acid and postulated the following dissolution reaction: …”

“…This assumption seems to be found- [45] and 72.2 eV (Pt(OH) 2 ), [45] and two 4f 5/2 peaks located at 74.6 eV (Pt 0 ) and 75.6 eV (Pt(OH) 2 ) binding energy, respectively (f). ed [53][54][55] for example, Mitsushima et al [53] investigated the dissolution of Pt in the presence of O 2 in sulfuric acid and postulated the following dissolution reaction:…”

Is platinum a suitable counter electrode material for electrochemical hydrogen evolution reaction?

“…For revealing this complete Pt dissolution mechanism, enormous research efforts have been made to evaluate the characteristics of these surface oxides (i.e. PtO x , x = 1 or 2), the valence of the dissolved constituents, the influence of potential change, temperature, pH, and the mass-transport on the reactions participated [2][3][4]. Evidently, Pt is not as stable as it is anticipated.…”

“…However, further experimental results demonstrated that not only in the acidic, but also in the alkaline media, both electrochemical and chemical dissolution of Pt would lead to the deposition of Pt on the working electrode if there is not any ion exchange membrane employed in the electrochemical setup. In consideration of these results obtained, they finally gave several valuable suggestions: (1) purifying the electrolyte before HER process, (2) replacing the Pt with other stable counter electrodes, (3) applying the ion exchange membrane to the setup preventing the Pt transfer across the working and counter electrodes.…”

From Bad Electrochemical Practices to an Environmental and Waste Reducing Approach for the Generation of Active Hydrogen Evolving Electrodes

“…We claim herein that platinum oxide species formed on the Pt anode may be dissolved in the H 2 SO 4 and cationic Pt oxide species can be electrodeposited on the Ni42 steel (Figure f). This assumption seems to be founded for example, Mitsushima et al . investigated the dissolution of Pt in the presence of O 2 in sulfuric acid and postulated the following dissolution reaction: …”