Among the best performing set of co

Among the best performing set of conditions in terms of both Faradaic efficiency and partial current density to ammonia were those at a nitrate concentration of 0.4 M in strong acid. To further improve these two metrics, we ran a set of experiments using a Nafion membrane divider and a platinum counter electrode in our electrochemical cell with two 20 sccm Ar inlet streams for the catholyte and anolyte (Ti/Nafion/Pt setup), rather than the membrane-less cell and glassy carbon counter electrode with a single inlet stream of 20 sccm Ar (Ti/GC) setup of the heatmap experiments. The Nafion membrane was employed as a physical barrier to inhibit the crossover of the ammonia product or partially reduced intermediates, which may otherwise be oxidized at the counter electrode. Platinum is a preferred standard counter electrode choice as it was a significantly more active and stable oxygen evolution catalyst under our experimental conditions compared to glassy carbon. However, it is important to mitigate Pt crossover and deposition on the cathode because platinum is also known to be an exceptionally good HER catalyst. Fortunately, the Nafion membrane also inhibits this crossover process, thereby preventing an unstable increase in H2production due to Pt deposition on the cathode. It is important to note that Nafion is known to be problematic for ammonia detection at low concentrations due to ammonia contamination and triggering of the colorimetric test used to quantify NH3yields.44,45 Therefore, we chose to use both a glassy carbon counter electrode and a cell without a Nafion membrane to avoid NH3 contamination in the heatmap experiments, despite the likelihood of lower efficiency and activity metrics. Under the high ammonia production conditions used with the Ti/Nafion/ Pt system, any such contamination was negligible.