Recent Advances in 3d-Block Transition Metal-Based Catalysts for Electrochemical Nitrate Reduction to Ammonia

Ammonia (NH3) is a crucial chemical in modern industry, serving as a key component in fertilizers and emerging as a potential energy carrier. However, traditional NH3 synthesis via the Haber-Bosch process is highly energy-intensive and contributes significantly to global CO2 emissions. Electrochemical nitrate reduction reaction (NO3RR) has emerged as a sustainable alternative for NH3 production, leveraging renewable electricity to reduce nitrate (NO3−) under ambient conditions. Among various electrocatalysts, 3d-block transition metal-based materials have shown remarkable potential due to their low cost, electronic structures, redox flexibility, and tunable catalytic properties. This review provides a comprehensive analysis of recent advances in 3d-block transition metal-based catalysts for NO3RR, highlighting catalyst design, performance metrics, mechanistic insights, and challenges. Furthermore, strategies such as alloying, single-atom catalysts, and high-entropy alloys are reviewed to enhance efficiency and selectivity. Finally, we discuss future perspectives on catalyst development and practical application in green NH3 production, aiming to bridge the gap between fundamental research and industrial applications.