Levitation-guided disorder engineering unlocks efficient nitrite-to-ammonia electroconversion

Abstract

Electrocatalytic conversion of nitrite (NO₂⁻) to ammonia (NH₃) via the NO₂⁻ reduction reaction (eNO₂RR) presents a promising approach. Prussian blue analog (PBA)–based electrocatalysts are potential candidates for eNO₂RR owing to their good activity and selectivity. Herein, to the best of our knowledge, for the first time, we report a facile synthesis of a flower-like copper (Cu)–cobalt (Co) PBA sulfide (CuCoPBA-S) using pulsed laser irradiation in liquid and investigate its formation mechanism using acoustic levitation coupled with in situ Raman spectroscopy. This approach enables contaminant-free, rapid, and cost-effective synthesis of electrocatalysts. The sulfurization process is shown to be time-dependent in the formation of ordered/disordered flower-like CuCoPBA-S structures. CuCoPBA-S considerably influences the eNO₂RR, achieving a NH₃ faradaic efficiency (FE) of 80.91% and an NH₃ yield rate of 3394.1 μg h⁻¹ cm⁻² at a fixed potential of −0.5 V vs. the reversible hydrogen electrode (RHE). Moreover, density functional theory analysis validates the eNO₂RR pathway facilitated by CuCoPBA-S during the electrocatalytic conversion of NO₂⁻ to NH₃, and the rate-determining step in the pathway is the hydrogenation of *NH₂O to *NH₂OH.

Keywords: Prussian blue analog; Acoustic levitation; Nitrite reduction; Electrocatalysis; Ammonia synthesis.