Harnessing Solar Energy for Ammonia Synthesis from Nitrogen and Seawater Using Oxynitride Semiconductors

Abstract

Green ammonia evolution by photocatalytic means has gained significant attention over recent decades, however, the energy conversion efficiency remains unsatisfactory, and deep mechanistic insights are absent. Here in this work, this challenge is addressed by developing a photothermal system that synthesizes ammonia from nitrogen and natural seawater under simulated solar irradiation, employing ruthenium-doped barium tantalum oxynitride semiconductors. This method significantly enhances solar-to-ammonia conversion efficiency, providing a viable alternative to the energy-intensive Haber–Bosch process. Optimized at 240 °C, the system achieves an ammonia evolution rate of 5869 µmol g⁻¹ h⁻¹ in natural seawater. Moreover, detailed characterizations have shown that the use of seawater not only leverages an abundant natural resource but also improves the reaction kinetics and overall system stability. The catalysts maintain their activity and structural integrity over multiple cycles, demonstrating both the feasibility and the durability of this innovative system. Achieving a solar-to-ammonia efficiency of 13% and an overall energy conversion efficiency of 6.3%, this breakthrough highlights the potential to decentralize ammonia production, enhancing accessibility and sustainability. This approach combines the benefits of thermal and photocatalytic processes, marking a significant advancement in ammonia synthesis technology.