In this report, we resolve the EC ambiguity of a-TiO2 protected photocathodes by using a model p-Si system. Investigation of the effect of different overlayers on both device performance and corresponding impedance response reveals that the ambiguity arises from the presence of a-TiO2 itself. Furthermore, using the well-defined properties of crystalline silicon, we show that of the three possible ECs with which to model these devices, the Maxwell circuit is the only one to show consistency between devices with and without the a-TiO2 protection layer. Therefore, in addition to the long-range conduction of electron transfer during hydrogen evolution, a parallel charging process also occurs in these devices. This charging process is investigated by first removing intercalating species from the electrolyte solution, and also by interrupting communication between the p-Si substrate and a-TiO2 protection layer.