Catalytic Metal Foam by Chemical Melting and Sintering of Liquid Metal Nanoparticles

Metal foams are highly sought-after porous structures for heterogeneous catalysis, which are fabricated by templating, injecting gas, or admixing blowing agents into a metallic melt at high temperatures. They also require additional catalytic material coating. Here, a low-melting-point liquid metal is devised for the single-step formation of catalytic foams in mild aqueous environments. A hybrid catalytic foam fabrication process is presented via simultaneous chemical foaming, melting, and sintering reaction of liquid metal nanoparticles. As a model, nanoparticles of tertiary low-melting-point eutectic alloy of indium, bismuth, and tin (Field's metal) are processed with sodium hydrogen carbonate, an environmentally benign blowing agent. The competing endothermic foaming and exothermic sintering reactions are triggered by an aqueous acidic bath. The overall foaming process occurs at a localized temperature above 200 °C, producing submicron- to micron-sized open-cell pore foams with conductive cores and semiconducting surface decorations. The catalytic properties of the metal foams are explored for a range of applications including photo-electrocatalysis, bacteria electrofiltration, and CO2 electroconversion. In particular, the Field's metal-based foams show exceptional CO2 electrochemical conversion performance at low applied voltages. The facile process presented here can be extended to other low-temperature post transition and transition metal alloys.