How the ionic liquid [C₂C₁Im][OTf] affects the stability of Pt(111) during potential cycling

Modifying electrocatalysts with ionic liquids (ILs) not only allows for precise control of selectivity but also often directly impacts the stability of the electrocatalyst. In this work, we study how the IL 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C₂C₁Im][OTf] influences the electrochemical stability of the Pt(111) surface in acidic electrolyte (0.1 M HClO₄) during oxidation and reduction cycles (ORCs; 0.05-1.5 V_RHE). We used complementary electrochemical in situ methods, namely, cyclic voltammetry (CV), online inductively coupled plasma mass spectrometry (ICP-MS), and electrochemical scanning tunneling microscopy (EC-STM) in combination with an algorithmic pattern recognition approach. In the absence of the IL, Pt(111) dissolves during oxidative cycling via cathodic transient dissolution. In consecutive cycles, small Pt clusters are formed, which grow with increasing cycle number. In the presence of the IL, the dissolution rate increases by a factor of 5 and an additional anodic dissolution pathway occurs. The changes in the dissolution behavior during ORCs, however, have only minor impact on the morphological changes and the adsorption sites formed. We explain latter observation by the dominance of morphological changes due to the formation and reduction of an amorphous oxide layer, as opposed to dissolution and redeposition.