Optimizing dual-active-site electrocatalysts for adsorption and hydrogenation for efficient nitrate-to-ammonia

Designing dual-active-site catalysts is critical for electrochemical reactions that involve multiple reaction steps, such as the adsorption and hydrogenation steps for the electrocatalytic nitrate reduction reaction (NO₃RR) to ammonia (NH₃). Although Co-based electrocatalysts are widely studied for their hydrogenation capability, their performance is often limited by weak NO₃⁻ adsorption and slow intermediate transfer. Herein, we designed a FeCo hollow nanocube (denoted as FeCo-NC) as novel high-performance NO₃RR electrocatalysts with dual active sites. Specifically, the Fe sites promote NO₃^- adsorption and activation, while Co sites facilitate water dissociation to generate active hydrogen (*H) and promote hydrogenation of intermediates on Fe sites toward NH₃ formation. In-situ electrochemical spectra measurements and density functional theory (DFT) calculations confirm that by regulating the electronic structure between the Fe-Co bimetals, the doping of Fe effectively reduces the reaction energy barrier of the rate-determining step (*NO to *HNO). Consequently, the obtained FeCo-NC catalyst demonstrated outstanding performance with an ammonia production rate of 14.1 mg h^-1 cm^-2 and a Faradaic efficiency of 94.5% at -0.6 V (vs. RHE), which surpass the single-site catalyst without Fe doping (Co-NC). More importantly, the dual-active-site catalyst demonstrated a cycling stability of 20 h. The Zn-NO₃^- battery employing this optimized FeCo-NC catalyst as the cathode delivered a power density of 8.98 mW cm^-2. This work offers novel insights and design principles for dual active sites catalytic mechanisms and the development of high performance NO₃RR systems.