SPS Adsorption from the Electrolyte

In an electrolyte containing a dilute SPS concentration, disulfide adsorption occurs coincident with displacement of the less strongly bound PEG-based inhibitor. The adsorption or exchange process can be described by irreversible Langmuir kinetics [112,135, 281], The effective rate constant, fcads, is potential dependent, the rate increasing exponentially with overpotential T) according to 

Potential dependent halide adsorption, including order-disorder phenomena, is well known [134, 246, 247], and it is reasonable to expect that the breakdown of the PEG-C1 blocking layer might also be potential dependent. In a similar fashion, the composition and structure of thiols and disulfides adsorbed on gold from simple electrolytes have been shown to be potential dependent [282]. In the present example, it is also possible that the approach of SPS to the electrode surfaces is screened by complexation with the potential dependent concentration of Cu+ that is generated at the electrode. Importantly, the equilibrium Cu+ concentration in the additive-free system (i.e. Equations 2.1 and 2.2) is of the order of 400 (tmol L 1 and Cu+ is known to form complexes with all the additives under consideration [239, 279, 280, 283-285]. Furthermore, the equilibrium Cu+ concentration decreases exponentially with potential, that is, 60 mV per decade of concentration [283-285]. Thus, the increasing rate of SPS adsorption with 

As the rate constant kads increases rapidly with overpotential, the adsorption process must eventually become constrained at higher overpotentials by diffusion of SPS in the electrolyte. Mass balance between the catalyst accumulating on the interface and diffusing through the electrolyte is given by  

With the parameters, iPEGj oCpeg, isps, asps. fcmc(q) and q(q) derived from experiments using either freshly abraded or S PS-derivatized electrodes in S PS-free PEG-C1 electrolyte, the hysteretic q-i data for the full SPS-PEG-C1 electrolyte were used to fit 

Interest in using low add eledrolytes has developed and care must be taken to assay what, if any, effed pH will have on the optimization of the above chemistry [286, 287]. Likewise, attention must be given to the corred evaluation of kinetic parameters in the presence of significant ohmic losses associated with the lower condudivity electrolytes. 

---