The influence of electrolyte purity on electrochemical measurements using platinum electrodes

The influence of electrolyte purity on electrochemical processes at low-area platinum electrodes has been studied by a fast potential-step method and by cyclic voltammetry. Pre-purification of the electrolyte had no significant influence on the metal surface area available for H adsorption determined immediately after an electrochemical cleaning step. Maintaining the electrode potential within the ‘double-layer’ region of platinum (at 0.5 V vs rhe) for relatively long periods of time (1–30 min) results in the progressive suppression of H adsorption, owing to the adsorption of impurities blocking active Pt sites. All samples of electrolyte, irrespective of the degree of pre-purification, exhibited this effect. In the determination of current-time transients during the first few hundred milliseconds of the methanol electro-oxidation reaction, impurities in the untreated electrolyte contribute to the measured anodic currents at Pt electrodes working in the potential range of 0.4–0.6 V. The anomalous effects observed within this potential range can be largely eliminated by pre-electrolysis of the H₂SO₄ electrolyte for several days using Pt wire gauze electrodes at 2.1 V.