Borohydride Hydrolysis Using a Mechanically and Chemically Stable Aluminium-Stainless Steel Porous Monolith Catalyst Made by 3D Printing

The challenge of moving to a carbon-free energy economy is highlighted in the context of technology and materials restrictions. Many technologies needed for the so-called energy transition depend on critical metals such as platinum, lithium, iridium and cobalt. Here we focus on solid borohydride salts as hydrogen carriers, studying catalysts for hydrogen release. We combine metal 3D printing technology and a Raney-type leaching process to make structured macroscopic catalyst/reactor monoliths of cobalt, aluminium and stainless steel with well-defined micropores. Remarkably, the blank catalyst samples, which are made only from aluminium and stainless steel (Al-SS), show high activity and, importantly, high stability in borohydride hydrolysis, with no mass loss and no surface poisoning. The batch results are confirmed in a continuous setup running for 96 h. Catalyst performance is attributed to the stable porous structure, the mechanical stability of the stainless steel macrostructure, and the presence of accessible Al(OH)x sites. This research shows a clear contribution to sustainability based on multi-factor comparison: The Al-SS catalyst outperforms the state-of-the-art on mechanical and chemical durability, it is both PGM-free and CRM-free, and its preparation follows a simple, scalable and low-waste procedure.