PH dependence of noble metals dissolution: Platinum

Abstract

Obtaining new information about the dissolution behavior of platinum in different pH conditions can help understand the stability of this metal in a wide variety of electrochemical devices. In this work, Pt dissolution is investigated in a pH range from 0 to 12.7 applying on-line inductively coupled plasma mass spectrometry (ICP-MS) with phosphate buffer solutions in an electrochemical scanning flow cell (SFC). Various electrochemical protocols are employed, including slow cyclic voltammetries at 5 mV s-1 and potential steps up to 1.2 and 1.6 VRHE. Results for total Pt dissolution show an inverted volcano dependence with pH in all cases, with the minimum dissolution located at pH = 7. Dissolution for pH = 0 is considerably higher than for pH = 1. In the case of the cyclic voltammetry experiments, the changes in dissolution are mainly due to the cathodic dissolution contribution. Interestingly, when phosphoric acid is used for the electrolyte with pH = 1, cathodic dissolution is higher than for the perchloric acid case. When comparing a slow reductive ramp to a direct potential jump after holding the electrode at oxidative potential, the results point out that dissolution is much higher for the slow reductive ramp in the case of acidic pH values. The results presented in this work can help improve the fundamental understanding of Pt dissolution since it is the first time such an exhaustive pH study has been carried out for on-line potential resolved experiments.