Comparing electro- and thermo-catalytic ammonia decomposition, a crucial component in the green ammonia value chain as an H2 vector.

Ammonia decomposition (cracking) is a crucial step in the ammonia value chain for its use as an H2 carrier. Thermocatalytic ammonia decomposition is the main route under investigation, with electrocatalysis as an emerging direction. However, due to the drastic differences in operating conditions, comparing these routes and the third alternative, membrane-assisted thermocatalytic ammonia decomposition, to determine which offers a better prospect is challenging. Here, we have compared Pt(100)/C, Pt-Ru/C, and Ru/C nanoparticles supported on conductive carbon as benchmark materials to facilitate direct comparison and have also developed a method to enable it. It was found that the thermocatalytic route is preferable to the electrocatalytic one. Although the latter still yields inferior overall productivity, performance is comparable under some conditions, indicating the direction toward superior process intensification through electrocatalysis. Notably, integrating an H2-permeable membrane into the thermocatalytic route allows a substantial reduction in operating temperature while preserving catalytic performance. The Ru catalyst performs better than the others in both thermo- and electrocatalysis, but for different mechanistic reasons. In particular, the behavior in electrocatalysis is determined by its superior ability to promote both anodic water electrolysis and ammonia electrolysis. However, Ru also has other limitations to consider when used as the preferred metal choice.