Mortar Synthesis: A Mechanochemical Approach to Metal Aerogel Production

Metal aerogels are versatile materials that bind the nanoparticulate properties of their building blocks in a self-supporting macroscopic body. Their large specific surface area (SSA), conductivity, and electrocatalytic activity make them highly attractive for a wide range of applications. High production rates are, therefore, equally important. To this end, we report a unique approach to synthesize metal aerogels in a mortar, operating at the highest metal precursor concentrations currently reported. The metal precursor and NaBH₄ are ground together, initiating partial reduction by mechanochemical activation, followed by adding water to complete the reduction. In this way, aerogels are successfully prepared from all nonradioactive metals of groups 8-11, for the first time from the main group elements In, Sb, Pb, Bi, and bimetals thereof. Particularly, the Fe aerogel morphology can be altered between random interconnected networks and nanochain bundles under the influence of an external magnetic field. Depending on the element, SSAs between 2 and 70 m²/g and ligament sizes of 2-140 nm were achieved. On top of this great versatility, gelation times are often unprecedentedly fast, i.e., almost instantaneous, and easily achieve remarkably high state-of-the-art production rates of at least 10 mmol per batch, often with minimal trade-off in ligament size and SSA.