Solar-driven direct coupling of atmospheric CO₂ with ammonia for urea synthesis.

Abstract

Current CO₂ utilization depends on high-purity CO₂, necessitating energy-intensive capture and purification from air. Herein, we present a practical system that selectively converts atmospheric CO₂ with ammonia into urea using solar energy as the sole input. This system is enabled by a heterostructure composed of an indium-porphyrin metal-organic framework and UiO-66-NH₂, which harness ambient O₂ to promote rather than suppress CO₂ reduction. As a result, it achieves a CO production rate of 272.1 μmol·g^-1·h^-1 directly from air, which is competitive compared to the systems that rely on high-purity CO₂. Moreover, coupling atmospheric CO₂ reduction with ammonia oxidation enables direct air-to-urea conversion with high selectivity. A scaled-up prototype operating under natural sunlight and open-air conditions achieves a urea production rate of 32.4 μmol·g^-1·h^-1. This work integrates atmospheric CO₂ capture, solar-driven conversion, and product collection within a single, scalable platform, offering a practical route for carbon utilization under real-world conditions.