Enhanced ammonia electrosynthesis over phosphorus-doped nickel across broad nitrate concentrations via regulating trade-offs in pathways

Electrocatalytic nitrate reduction reaction (NO 3 RR) holds promise for carbon-neutral ammonia production but requires efficient electrodes to minimize the formation of nitrite and hydrogen by-products, from either concentrated or dilute feedstocks. Here, we report a trade-off effect upon phosphorus incorporation into Ni, wherein Ni- and P-rich surfaces tend to inhibit nitrite and hydrogen formation, respectively, while promoting the generation of the respective opposite by- products. Under 0.1 M nitrate concentration, the selectivity switch between the by-products presented a correlation with the intrinsic HER activity of surfaces, highlighting the critical role of *H supply. Through ex-situ and in-situ spectroscopies, the reconstructed P-doped Ni (R-NiP) was found to exhibit an oxidation state and local atomic environment intermediate between those of Ni and P-doped Ni (NiP), effectively integrating the suppressing traits of both Ni and P. Consequently, an ammonia Faradaic efficiency of 89 % was achieved at a reduced potential on R-NiP, along with a 2- and 8-fold enhancement in intrinsic activity compared to NiP and Ni, respectively. By leveraging this trade-off, we also showcase the adaptability of NiP platform for effective operation across both lower and higher nitrate concentrations, emphasizing that nitrate bulk concentration should be factored in when regulating *H supply for efficient ammonia electrosynthesis. • Nitrate reduction to ammonia is enabled on a modified nickel catalyst. • An ammonia production rate of 2.462 mmol h −1 cm −2 was achieved on R-NiP sample. • Efficient ammonia production requires a balanced availability of nitrate and *H. • Promoting the supply of *H does not inherently yield positive outcomes. • Managing *H supply must be done with consideration of nitrate bulk concentration.