Understanding the Morphogenesis of Hierarchically Porous Graphitic Aerogels Produced from Protein Precursors

Abstract Hierarchically porous graphitic sheet-based aerogels with high surface area and ultra-low density have drawn massive attention for applications in catalysis, energy storage/conversion, water purification, and beyond. Single-step pyrolysis of protein precursors for creating hierarchically porous monolithic graphitic aerogels with exceptional electrical, electrochemical, and mechanical properties has emerged as a sustainable and green approach. However, the formation mechanisms underlying the transformation of proteins into these aerogel structures remain to be understood. Herein, we demonstrate a self-foaming mechanism for the green and scalable synthesis of hierarchically porous monolithic sheet and fiber-structured graphitic aerogels using protein as a precursor. Rather than creating a solid phase and then exchanging the sacrificial component for a gas phase, we create a gas phase and then convert the liquid into a solid phase. The controlled heating of the protein precursors induces an intrinsic foaming action via initial softening followed by gas evolution and graphitization, resulting in a hierarchically porous graphitic aerogel composed of an integrated sheet and fiber framework. Our systematic exploration into the processing-structure-property relationships that govern aerogel optimization elucidates the interplay between tunable synthesis variables and resultant aerogel properties and structure, enabling deliberate control over microstructural features.