CV was performed at 10 mV/s in quiescent and 500-rpm stirred NaxH3-xPO4 (dibasic sodium phosphate monohydrate (Na2HPO4 x H2O), Fischer Chemical, Certified ACS Grade; monobasic sodium phosphate (NaH2PO4), Fischer Chemical, Certified ACS Grade) aqueous solution with a series of sodium nitrate (NaNO3; EMD Millipore, ACS Grade) concentrations, with reported data representing a reproducible trace. Steady-state CA measurements were performed for 30 s per potential in 40 mV increments with a stir bar rotating at 500 rpm to mitigate mass transfer limitations. The voltage range for each TM foil was chosen to observe phosphate-deprotonation and water-dissociation mediated hydrogen evolution (HER), limiting the anodic potential to exclude the formation of surface oxides (excluding Ti which forms surface oxides or hydrides 1 across the potential range considered here). Potentials of CV and Supplementary Information Page 3 of 49 CA measurements have been corrected for solution and contact resistance (iR) losses by identifying the real impedance contribution from potentio electrochemical impedance spectroscopy (PEIS). Current has been normalized by the geometric surface area (cm