The electrochemical hydroxylation of H-terminated n-Si as revealed by a generalized phase analysis of EIS: Real time detection

Based on the conceptual generalization of a constant phase element (CPE) an improved set of fractional-order functions is defined to describe the flow and accumulation of charge in an electrochemical interface, as measured by EIS. The so-called gpe method has five major advantages: (i) it is a differential analysis, which enables the detection of subtle faradaic reactions; (ii) it generates a dispersionless interfacial capacitance whenever the system is in a blocking state; (iii) it gives a better estimate for the electric double layer capacitance than the widely accepted Brug's expression; (iv) it allows real-time tracking of a moderately fast evolving system; (v) it is model-free. The far-reaching benefits of the gpe method will be demonstrated by analyzing the impedance evolution of an H-terminated n-Si (100) electrode under the action of a staircase anodic potential scan in a fluoride-free aqueous electrolyte in the dark. It will be shown that this interface undergoes an electrochemical hydroxylation reaction involving a hole, a dangling bond and an electron.