Ultralight and compressible mussel-inspired dopamine-conjugated poly(aspartic acid)/Fe³⁺-multifunctionalized graphene aerogel

The reduced graphene oxide (rGO) aerogels are particularly attractive owing to their ultralight-weight, high surface area and interconnected macroporosity for energy storage applications. However, pure rGO aerogels are generally weak and brittle to limit their practical applications. To overcome this drawback, a small amount of synthetic dopamine-conjugated poly(aspartic acid) was mixed with graphene oxide to fabricate ultralight rGO aerogels with high porosity and mechanical integrity via hydrothermal reactions at 80 °C and freeze-drying process. In addition, the Fe³⁺ ionic species was chosen for an additional cross-linker to further strengthen the ultralight poly(aspartic acid/dopamine) functionalized rGO aerogel, abbreviation for PAAD/rGO, through the coordination bonding between Fe³⁺ and carboxylic acid or catechol groups of both polymer and rGO sheets at pH 9 (PAAD/rGO-Fe❾). The hybrid electrodes of PAAD/rGO-Fe❾ showed the reversible transformation of the Fe³⁺ tris-catecholate complexes into mono-catecholate promoting Quinone (Q)-hydroquinone (QH₂) in 1.0 mol L⁻¹ H₂SO₄ electrolyte, thus delivering a high specific capacitance of 276.4 F g⁻¹ at 0.5 A g⁻¹ and capacitance retention of 88.2% after 5000 cycles. Moreover, this compressible aerogel provided high strength with 150 kPa without noticeable structural fracture after 80% compression and repeated deformation processes suggesting applications in energy storage and absorption.