Additionally, O-upd formed at higher potentials cannot be reduced in the cathodic scan, leading to an irreversible increase of the apparent surface area, obfuscating the state of the surface (not shown). ( ) The slow oxidation of the hydride formed on Pd(pc) at low potentials (< 400 mVRHE) limits the potential window. Additionally, while the relative O-upd reduction peaks follow the expected trend (Rh(pc) < Ir(pc) < Pd(pc) < Pt(pc) < Au(pc)) from the lattice constants, the transition from the DL capacitance to the O-upd on Pd(pc) is remarkable: The DL charge is very close to that of Au(pc) over a range of 200 mV with a very sharp transition to the O-upd capacitance, also notable in the OCP-time transients. To the author's knowledge, this phenomenon's origin is unclear.