Tandem plasma electrocatalysis: An emerging pathway for sustainable ammonia production

Abstract

The Haber-Bosch process, the dominant process for industrial ammonia production, is highly energy-intensive and a major source of carbon emissions. Plasma and electrocatalysis offer viable and promising alternatives for nitrogen reduction reactions, especially when integrated with intermittent renewable electricity. However, relying solely on plasma or electrocatalysis for direct N₂ reduction presents significant challenges. Plasma technology suffers from low conversion efficiency and high energy consumption. Similarly, electrocatalysis encounters challenges with low yield and Faradaic efficiency, primarily due to the low solubility of nitrogen gas and interference of the competing hydrogen evolution reaction. A tandem process combining plasma synthesis of NO_x (a mixture of NO and NO₂) with the electrochemical NO_x reduction reaction (eNO_x⁻RR) can effectively use NO_x as an intermediate, thereby significantly reducing the difficulty of N₂ activation in plasma and enhancing the Faradaic efficiency of the subsequent electrocatalytic process. This promising solution has great potential to dramatically enhance the ammonia synthesis rate, making the tandem process a compelling technology for sustainable and decentralized ammonia synthesis under mild conditions. This review provides an insightful overview of the tandem plasma-electrocatalytic process, illustrating the reported methods for plasma-driven nitrogen activation to nitrogen oxides and discussing the recent advances and challenges in eNO_x⁻RR, with a particularly focus on developing efficient electrocatalysts. Additionally, we discuss the systemic challenges of integrating these two processes, highlighting the importance of process optimization and the potential for ammonia production. The techno-economic and environmental impacts of the tandem process are also evaluated and compared to the Haber-Bosch process, providing insights into future development pathways for this innovative approach.