Degradation of the Pt/C air cathode in acidic solution examined by cyclic thermammetry

The oxygen reduction reaction on carbon-supported platinum electrocatalysts (Pt/C) has been investigated as a function of temperature by employing the technique of cyclic thermammetry. A novel electrochemical cell has been designed which allows the concomitant measurement of the potentiostatic current from the oxygen reduction reaction (ORR) and accurate control of the aqueous electrolyte temperature, allowing cyclic linear temperature sweeps between 25 and 80 °C at speeds up to 40 mK s−1. Our method provides new insight into the temperature dependent degradation of the cathodic oxygen reduction reaction in aqueous sulfuric acid systems. Cycling the temperature accelerates the degradation of the cathodic current through loss of active surface area. Two simultaneously operating mechanisms are proposed to account for this loss. One mechanism is described by physical detachment of the platinum and carbon particles under thermal fatigue, and the other by anodic dissolution of the Pt electrocatalyst. The forms of these are discussed.

► A new experimental method allowing cyclic thermammetry to be used for fuel cell analysis.
► Frequency-dependent degradation of a Pt/C air cathode is observed.
► Thermal fatigue of the Pt/C interface is identified as a mechanism of degradation, which operates simultaneously with anodic dissolution.
► Loss of performance with time quantified with loss of catalytic surface area.