Electroreduction from Nitrite to Ammonia over Cobalt Sulfide Nanorods on Nickel

Electrochemical nitrite reduction reaction (NO₂RR) can meet the need to remove nitrite (NO₂^–) pollutants and provide a sustainable way to produce ammonia (NH₃). However, the conversion process from NO₂^– to NH₃ is a complex multistep process involving six-electron transfer, posing a significant challenge for designing efficient catalysts for the NO₂RR. Here, a series of cobalt-based sulfide (Co_xS_y) nanorods (NRs) anchored on nickel foam (NF) with varying sulfur contents (CoS_1.035 NRs/NF, CoS₂ NRs/NF, Co₃S₄ NRs/NF, and CoS_1.097 NRs/NF) were synthesized through phase-controlled synthesis. The optimal cobalt-based sulfide nanorods (CoS₂ NRs/NF) exhibit superior performance in the NO₂RR, with an extremely high NO₂^– conversion rate (97.8%), Faradaic efficiency (97.9%), and NH₃ selectivity (98.7%). These results surpass those of previously reported NO₂RR catalysts. Controlled experiments confirm that for the different cobalt sulfide phases, the higher the sulfur content, the more active hydrogen produced, which is more conducive to the electroreduction from NO₂^– to NH₃. This research presents novel insight into the rational design of NO₂RR catalysts.