XPS revealed the concentration of cations in the polymer films to continually decrease with decreasing PSS mol fraction, with no Rb + cations present in the 0.0 PSS mol fraction electrodeposited PEDOT film (Figure ). The presence of Br -anions decreased with increasing PSS mol fraction and was suppressed to concentrations below the detection limit above 0.6 PSS mol fraction (>50% sulfuric acid treatment concentration, Figure ), representing the threshold beyond which fixed cationic charge density was sufficient to exclude mobile anions. These trends were further confirmed with benchtop XRF measurements (Figure ), with some variation in Rb + concentration at high PSS mol fraction.