Cu/Cu⁺ Synergetic Effect in Cu₂O/Cu/CF Electrocatalysts for Efficient Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction reaction (NO₃^-RR) has been considered a promising technology to produce ammonia but is inhibited by poor electrocatalytic performances. Therefore, the development of efficient electrocatalysts and investigation of corresponding reaction mechanisms are critically important. Herein, an efficient dendritic Cu₂O/Cu grown on Cu foam (D-Cu₂O/Cu/CF) has been synthesized by a facile electrodeposition method, and the synergetic effect of Cu and Cu⁺ in NO₃^-RR has been investigated. In situ and ex situ data testify the synergetic effect clearly that Cu sites are responsible for the beginning of nitrate conversion to nitrite, while Cu⁺ sites are the active center for subsequent nitrite reduction to ammonia. In addition, in situ-generated active Cu⁺ sites further enhance the catalytic performances. Therefore, an extraordinarily high nitrate removal rate of 98.9% together with a relatively high ammonia yield rate of 11.2 mg h^-1 cm^-2 can be obtained in electrolytes containing 90 ppm of nitrate.