Observation of monotonic surface charging at polycrystalline platinum-electrolyte interface using streaming current method

Abstract

Surface charging characteristics at polycrystalline Pt-electrolyte interfaces were studied using a novel combination of electrochemical techniques and electrokinetic streaming current methods developed by our group [Saha et al., 2019]. Surface charge typically increases with increasing electric potential on a metal, and this trend is commonly referred to as monotonic charging. Based on theoretical models, it was suggested that the Pt-electrolyte interface might deviate from this trend and have negative charge above the potential of zero charge (PZC) due to the metal's strong chemisorption properties [Huang et al., 2016]. We attempted to experimentally determine the validity of this claim using our method. In addition to the surface charging relations, we also quantified the effect of anion adsorption (oxide, chloride, sulfate) on surface charging. The experimental method also allowed us to observe the slow time-dependent growth of oxides on Pt surface. Since our first publication in 2019 [Saha et al., 2019], we were able to develop the setup to be more efficient that enabled us to apply higher potential on the metal, observe stronger ion adsorption effects on surface charging, and obtain more reliable data. Our recent experimental study shows that Pt charging remains monotonic and does not reverse due to chemisorption of oxides nor strong anion adsorption in the potential window where the charge reversal was theoretically shown to occur.