Electrochemical ammonia (NH₃) synthesis from nitrate (NO₃⁻) offers a promising greener alternative to the fossil-fuel-based Haber-Bosch process to support the increasing demand for nitrogen fertilizers while removing environmental waste. Previous studies have mainly focused on designing catalysts to promote the direct conversion (NO₃⁻ → NH₃) while suppressing the two-step pathway (NO₃⁻ → NO₂⁻ → NH₃). We hypothesize that efficient nitrate reduction is possible on simple catalysts by instead promoting the two-step reaction and using chemical reactor principles in a membrane electrode assembly, despite NO₂⁻ intermediates. Here, we use an unmodified copper catalyst and control reactivity through current density, flow rate, and electrolyte recycling. Balancing the electrolyte flow rate with current density results in ideal residence times for NO₂⁻, allowing for 91% FE_NH3 in a 5 cm² electrolyzer with a NO₃⁻ to NH₃ partial current of 1.8 A. This work shows that traditional engineering principles can substantially boost the NO₃ reduction reaction, even for simple catalysts.

The electrochemical reduction of carbon dioxide (CO₂) to value-added chemicals is a promising strategy to mitigate climate change. Metalloporphyrins have been used as a promising class of stable and tunable catalysts for the electrochemical reduction reaction of CO₂ (CO₂RR) but have been primarily restricted to single-carbon reduction products. Here, we utilize functionalized earth-abundant manganese tetraphenylporphyrin-based (Mn-TPP) molecular electrocatalysts that have been immobilized via electrografting onto a glassy carbon electrode (GCE) to convert CO₂ with overall 94 % Faradaic efficiencies, with 62 % being converted to acetate. Tuning of Mn-TPP with electron-withdrawing sulfonate groups (Mn-TPPS) introduced mechanistic changes arising from the electrostatic interaction between the sulfonate groups and water molecules, resulting in better surface coverage, which facilitated higher conversion rates than the non-functionalized Mn-TPP. For Mn-TPP only carbon monoxide and formate were detected as CO₂ reduction products. Density-functional theory (DFT) calculations confirm that the additional sulfonate groups could alter the C−C coupling pathway from *CO→*COH→*COH-CO to *CO→*CO-CO→*COH-CO, reducing the free energy barrier of C−C coupling in the case of Mn-TPPS. This opens a new approach to designing metalloporphyrin catalysts for two carbon products in CO₂RR.