Chemical looping hydrogen production from ammonia and water: materials and technoeconomics†

Abstract

Ammonia (NH₃) is a promising hydrogen carrier due to high hydrogen density and established infrastructure. We present a novel chemical looping process to produce H₂ from NH₃ oxidation and decomposition and from water splitting, integrating thermochemical redox looping and catalytic reaction. Unlike single-step catalytic NH₃ decomposition, the looping configuration produces high purity H₂ from the water splitting that significantly lowers separation energy and cost. FeO_x/YSZ and Fe_0.5Co_0.5O_x/YSZ were shown as durable dual-functional oxygen carriers and catalysts, achieving 95% and 99% NH₃ conversion and 39% and 25% water splitting conversion, respectively. The materials’ redox capacities were explained by simultaneous Fe and Co redox reactions and solid-state phase transition between metal (alloy) and spinel. From 450 to 600 °C, Fe redox capacity increased, while Co redox capacity decreased. Kinetic limitations hindered full reduction of FeO_x/YSZ to metallic Fe at 450 °C due to lack of the effective Co catalyst, while thermodynamic limitations prevented complete oxidation of Co metal in Fe_0.5Co_0.5O_x/YSZ. Techno-economic analysis showed the looping process achieves 52% to 86% lower energy and equipment costs than single-step catalytic NH₃ decomposition with different H₂ separation methods.