<p>Nitrogen cycle electrochemistry involves important reactions such as ammonia synthesis from dinitrogen or from nitrates and the oxidation of hydrazine or urea fuels. Many of these applications require the reliable detection of ammonia and the precise reporting of applied potentials. We now report that a commercial reversible hydrogen electrode catalyzes an undesired chemical reaction between hydrogen (from the electrode cartridge) and NO_x anions (from the electrolyte), generating ammonia in the absence of any applied potential. In addition to skewing the reported ammonia yields, this leads to a&#xa0;mixed potential and wrong reports of electrocatalytic onset potentials, compromising the measurements on several levels. Awareness and mitigation of these ubiquitous effects will allow nitrogen cycle electrocatalysis studies to advance on solid ground.</p>