Powder-bed-fusion-inspired additive manufacturing of freeform graphene aerogels via laser upcycling of biowaste hemoglobin protein

Three-dimensional (3D) cellular monoliths of graphitic materials, or graphitic aerogels (GAs), exhibit unique material properties offering applications in catalysis and energy storage. While conventional solution-based techniques enable the mass-production of GAs, the resulting features are highly randomized, and architecture-tunability had remained a challenge. Recently, the use of additive manufacturing (AM) towards the 3D printing of freeform GAs has been explored. The AM-printed GAs exhibit considerably improved performances, reinforcing the value of architecture-engineering capabilities. In this study, we demonstrate the laser-based 3D printing of freeform GAs by employing the concept of laser-based powder bed fusion (PBF) using hemoglobin as the feedstock material, an iron-containing protein found in red-blood cells. Hemoglobin is an abundantly available biomass that is a common biowaste of the meat industry, with millions of tons discarded yearly. Analogous to conventional PBF, a bed of the low-value biowaste was deposited, and subsequently irradiated to convert and assemble a 3D cellular monolith composed of turbostratic graphite. This process can be easily scaled up by simply depositing another layer of hemoglobin powder and subsequently scanning the laser beam. Through the repetition of these steps, a 3D macrostructure with arbitrary micro-scaled cellular geometries can be printed through a layer-by-layer approach. The laser printed macrostructures exhibited a low density, high electrical conductivity, and high surface area, suitable for energy-storage applications. The current PBF-inspired technique offers the freeform printing of GAs without any additional templates, binders, or chemical solutions, and the renewable resource, hemoglobin, is the only raw material required for the entire printing process.