Balancing sub-reaction rates for selective urea electrosynthesis by supported Ni/Rh nanoalloy catalyst

Ni/Rh nanoalloy matches the rates of two sub-reactions for urea electrosynthesis. • Rh-driven *CO dispatching redirects the reaction pathway from CO to urea. • Comprehensive in situ ATR-SEIRAS elucidates the distinct roles of Ni and Rh. • The FE Urea /FE CO for Ni/Rh nanoalloy boosts 30 times than that of Ni-BNC. The electrocatalytic co-reduction of CO 2 and nitrate (NO 3 - ) presents a sustainable route for urea synthesis, yet it is severely hampered by mismatched activation rates of the two sub-reactions (CO 2 reduction reaction and nitrate reduction reaction). Herein, building on our previous study of Ni-BNC for CO 2 to CO conversion, we constructed a Ni/Rh nanoalloy catalyst (Ni/Rh-BNC) via Rh-incorporation strategy to effectively redirect reaction pathway to urea from CO. Systematic in situ ATR-SEIRAS and Raman spectroscopy provide mechanistic insights into the intermediate evolution and reaction pathway switching. While Ni acts as a *CO generator, the incorporated Rh species serves a triple regulatory role: (i) activating NO 3 - to balance the two sub-reaction rates; (ii) stabilizing *CO intermediates generated from adjacent Ni sites via *CO transfer; and (iii) directly initiating C-N coupling to form urea. This Rh-driven *CO “dispatching” mechanism suppresses CO desorption and steers the pathway toward urea formation. Consequently, the urea-to-CO Faradaic efficiency (FE) ratio for Ni/Rh-BNC boosts nearly 30 times than that of Ni-BNC, achieving a urea FE of 31.2% at −0.7 V vs. RHE, with a maximum urea yield of 7981.8 mg·g metal −1 ·h −1 under low metal loading conditions. This strategy underscores a promising blueprint for rational catalyst design of dual metal sites enabling reaction pathway redirection and sub-reaction rate matching for multi-step electrocatalytic reactions. Download: Download high-res image (195KB) Download: Download full-size image