These three model systems illustrate the wide range of NO3RR reactant concentrations (NO 3 and H + equivalents) in potential feedstocks. Beyond these bulk descriptions, the consumption of 9/10 H + to produce NH3/NH4 + can locally increase the pH, particularly in circumneutral media with limited buffering (Fig. ) . Local pH increases are also tied to less cathodic potentials on the RHE scale (and therefore lower driving forces for NO3RR). While we suggest a 0.1 M phosphate buffer to help maintain the local pH, its ability to do so is tied to the rate of reaction and limited by mass transfer . For example, calculations with 0.1 M buffer pairs with a pKa of 7 can sustain only 10 mA/cm 2 at a rotation rate of 1600 rpm in rotating disk electrode (RDE) experiments while maintaining a difference in surface and bulk pH equal or less than 0.2 . The local pH can be measured using a rotating ring disk electrode , which may enable more representative understanding of the pH-dependent driving force. Variation in local pH towards more alkalinity may alter rate, FE, and selectivity uniquely compared to bulk alkaline conditions due to presence of a pH gradient.