In Situ Mineralization of Biomass‐Derived Hydrogels Boosts Capacitive Electrochemical Energy Storage in Free‐Standing 3D Carbon Aerogels

Here, a novel fabrication method for making free‐standing 3D hierarchical porous carbon aerogels from molecularly engineered biomass‐derived hydrogels is presented. In situ formed flower‐like CaCO 3 molecularly embedded within the hydrogel network regulated the pore structure during in situ mineralization assisted one‐step activation graphitization (iMAG), while the intrinsic structural integrity of the carbon aerogels was maintained. The homogenously distributed minerals simultaneously acted as a hard template, activating agent, and graphitization catalyst. The decomposition of the homogenously distributed CaCO 3 during iMAG followed by the etching of residual CaO through a mild acid washing endowed a robust carbon aerogel with high porosity and excellent electrochemical performance. At 0.5 mA cm −2 , the gravimetric capacitance increased from 0.01 F g −1 without mineralization to 322 F g −1 with iMAG, which exceeds values reported for any other free‐standing or powder‐based biomass‐derived carbon electrodes. An outstanding cycling stability of ~104% after 1000 cycles in 1 M HClO 4 was demonstrated. The assembled symmetric supercapacitor device delivered a high specific capacitance of 376 F g −1 and a high energy density of 26 W h kg −1 at a power density of 4000 W kg −1 , with excellent cycling performance (98.5% retention after 2000 cycles). In combination with the proposed 3D printed mold‐assisted solution casting (3DMASC), iMAG allows for the generation of free‐standing carbon aerogel architectures with arbitrary shapes. Furthermore, the novel method introduces flexibility in constructing free‐standing carbon aerogels from any ionically cross‐linkable biopolymer while maintaining the ability to tailor the design, dimensions, and pore size distribution for specific energy storage applications.