Rational design of high-index facet Cu₂O: Toward energy-efficient NH₃ electrosynthesis via HzOR coupling and advanced Zn-NO₂⁻ battery

The electrocatalytic nitrite reduction reaction (NO₂⁻-RR) presents a sustainable route to remediate nitrogen pollution and produce valuable ammonia (NH₃₎, yet its development is hindered by the lack of efficient catalysts. Herein, we fabricate cuprite nanostructures (Cu₂O NSs) with highly exposed high-index facets via a facile in-situ electrochemical reconstruction strategy. The catalyst exhibits an exceptional NO₂⁻-RR performance, achieving a remarkable NH₃ production rate of 5.02 mg h⁻¹ mg_cat⁻¹ with a Faradaic efficiency of 96.2% at −0.4 V. Experimental and theoretical results reveal that high-index facets such as (311) facets not only thermodynamically favor the adsorption and activation of key intermediates but also kinetically accelerate the reaction through rugged surfaces and porous architecture. By integrating the NO₂⁻-RR cathode with a hydrazine oxidation reaction (HzOR) anode, an electrolyzer was constructed for simultaneous NH₃ electrosynthesis and wastewater purification at an ultralow cell voltage of 0.19 V (10 mA cm⁻²), achieving an 83% reduction in energy consumption compared to conventional systems. An alkaline Zn-NO₂⁻ battery was further demonstrated, delivering a high open-circuit voltage of 1.312 V and a superior power density of 10.02 mW cm⁻², through which dual-functional nitrogen management and energy conversion are successfully realized.