Tailored copper-based cathode design advances economic viability of electrocatalytic nitrate treatment with ammonia recovery in a scalable flow reactor

Abstract

Electrocatalytic reduction is a promising alternative to remove nitrate (NO3–) from water and potentially recover value-added ammonia, but advancements are needed to reduce costs and promote technology adoption. Five monometallic catalysts on activated carbon cloth (ACC) electrodes were evaluated for electrocatalytic NO3– treatment in a previously developed scalable flow reactor. We report Cu and, for the first time, In (as In2O3) are the best performing catalysts regarding NO3– reduction activity (0.45–2.4 L gmetal–1 min–1), Faradaic efficiency (FE), and NH4+ selectivity, with intermediate NO2– accumulation using Cu and NH2OH using In. We discovered trace Pd addition (i.e., 0.01 wt%) to Cu eliminates NO2– accumulation, while approximately doubling activity, and boosting FE and NH4+ selectivity (99 %). Activity of Cu–Pd/ACC decreased with repeated treatment cycles but was easily recovered in situ via electrochemical regeneration. Electrocatalytic NO3– reduction costs with the Cu–Pd electrode were estimated less than IX or catalytic treatment, indicating economic viability.