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 (CoxSy) nanorods (NRs) anchored on nickel foam (NF) with varying sulfur contents (CoS1.035 NRs/NF, CoS2 NRs/NF, Co3S4 NRs/NF, and CoS1.097 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.