Two alternate protection layers were investigated. First, the Si native oxide (SiOx) was used as it is stable in the acidic solutions used here for the HER. Second, the a-TiO2 was crystallized at 500 °C, resulting in an anatase protection layer. In addition to changing the phase of the protection layer, this also removed the wide defect band in the TiO2 bandgap. The phase change and defect band removal are shown with XRD and XPS, respectively, in Figure .