The green production of ammonia (NH3) using nitrogen (N2) and steam (g-H2O) through electrocatalytic methods has been drawing significant amount of attention. The solid state electrolysis cells (SOECs) showed potential to produce NH3 with low cost and high production rate. The catalytical materials used are composed of co-doped lanthanum-chromite (La0.33Sr0.67Cr1-xFexO3-d, LSCrF) perovskite, and gadolinium-doped ceria (Ce0.9Gd0.1O2-d, GDC) fluorite. This combination was found to yielded series of unique electrocatalytic morphology and chemical properties, enabling the enhanced green NH3 production at the cathode compartment. An optimized ball milling approach (OBMA) was implemented to produce a series of cathodic composites. This OBMA synthesis and macro-porous structures collectively resulted in an improved intrinsic electrocatalytic property of LSCrF-GDC. The group invented an in-situ templating using a porogen with controllable size to facilitate gas diffusion and adsorption along with the interfaces of phase boundaries. The SOECs were then assembled and used for NH3 production with optimized synthesis and electrochemical measurement variables. These catalysts possessed high surface area and porosity, providing reactive sites for the reactants. Single atom modification further enhanced the production rate. Our data showed that the formation rate of NH3 was found to achieve &gt;3.0Χ10-10 mol s×cm-2 due to the formation of oxygen vacancies, high interactivity between catalysts and reactants, and gas channeling by the macro-porous structure. In short, this SOEC technology was able to provide a green approach to produce NH3, and overcome the drawbacks of the conventional production, such as clog pipelines and apparatus within a short time; relatively high pressure loss; dissociation of nitrogen triple bond.

Efficiency improvement of green catalytic synthesis of ammonia using solid oxide electrolysis cells

ACS Spring 2022

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