At this point, there is an opportunity to resolve the EC ambiguity of the p-Si│a-TiO2│Pt device during the HER. If the resistance associated with Si is expected to be the same regardless of protection layer, given very similar device performances, then Figure indicates that the Maxwell circuit is appropriate to describe device operation for the a-TiO2 protected devices. If not, the Voight circuit continues to be a valid option. Figure does highlight that altering the protection layer between c-TiO2 and SiOx does not change the resistance of Si significantly. However, as mentioned, the a-TiO2 has unique properties such as a defect band and the ability to intercalate ions that may affect device operation. Therefore, it is important to have a clear understanding of the physical mechanism of the Si resistance during device operation before determining the appropriate equivalent circuit.