The artificial nitrogen fixation has revolutionized agriculture and enabled the world population to grow to over 8 billion by 2024.^[1] Currently, 150 Mt of ammonia are produced by the energy-intensive and heavily CO₂-emitting Haber-Bosch process per year, of which 80 % is used for fertilizer production. However, less than 50 % of this ammonia reaches its end-use as nitrogen building block in crops while a high amount leaches into the environment and is present in the wastewater in form of nitrate.^[1,2]

The European environmental quality standard for nitrate in surface waters is at 50 mg l^‑1.^[3] However, in many regions this value is exceeded.^[3] It can seep into drinking water and thus cause health risks for humans.^[1] Using renewable energy, the electrochemical nitrate reduction (NO₃RR) provides an environmentally friendly way to clean wastewater and close the human-induced nitrogen cycle, moving towards a circular nitrogen economy. In the NO₃RR nitrate is employed as an abundant source for ammonia production or converted into the harmless dinitrogen.

Various catalysts have been investigated for NO₃RR. However, among the investigated materials Cu-based catalysts emerged to perform best.^[4] While the catalytic material itself plays a key role in the reaction, another important factor is the reaction environment. The choice of ionomer can affect ion transport, the local pH at the electrode surface, and the electrode porosity, thereby influencing both the activity^[5] and selectivity^[6] of the reaction.

Ionomers are commonly used in electrocatalytic systems as binders or membranes.^[7] Although, the absorption of ammonium and ammonium crossover by cation exchange membranes have been intensively studied in the literature for the electrochemical nitrogen reduction and NO₃RR, the effect of suitable binders has received too little attention.^[8] Furthermore, when choosing a suitable membrane, it is not only important to consider the ammonium crossover, but also other crossover effects. In NO₃RR research, chloride anions are commonly added to the electrolyte as common components of agricultural wastewaters in concentrations between 21-24 mg l^-1.^[9,10] Chloride can be oxidized at the anode to species that lead to the subsequent ammonia decomposition to nitrogen.^[9] Thus, the addition of chloride to the electrolyte is a common strategy to increase the selectivity of NO₃RR towards dinitrogen. However, the interactions between the chlorine species and different membranes, like crossover effects and membrane stability, require further attention.

In this study, the effect of ionomer choice, the correct electrode pre-treatment as well as the choice of membrane in an H-type cell regarding crossover effects of selectivity changing species are investigated. Preliminary results suggest that using a cation exchange ionomer (CEI) as binder and an appropriate pre-treatment of the electrode even in alkaline media increase the NO₃RR activity towards ammonia compared to using an anion exchange ionomer (AIM) binder.