We quantify the formation of nitrite and ammonium, the two primary products at the pH and low conversions measured here, over a series of commercial polycrystalline TM foils at a range of potentials as detailed in the Supplemental Information (SI). To better control nitrate conversion as a variable, a fixed charge is passed per nitrate anion (0.2 or 0.04 e -/NO3 -), corresponding to maximum 10 or 2% conversion of nitrate assuming 100% FE towards nitrite.