Stereolithography-Derived Three-Dimensional Pyrolytic Carbon/Mn 3 O 4 Nanostructures for Free-Standing Hybrid Supercapacitor Electrodes.

The development of permeable three-dimensional (3D) macroporous carbon architectures loaded with active pseudocapacitive nanomaterials offers hybrid supercapacitor (SC) materials with higher energy density, shortened diffusion length for ions, and higher charge-discharge rate capability and thereby is highly relevant for electrical energy storage (EES). Herein, structurally complex and tailorable 3D pyrolytic carbon/Mn 3 O 4 hybrid SC electrode materials are synthesized through the self-assembly of MnO 2 nanoflakes and nanoflowers onto the surface of stereolithography 3D-printed architectures via a facile wet chemical deposition route, followed by a single thermal treatment. Thermal annealing of the MnO 2 nanostructures concurrent with carbonization of the polymer precursor leads to the formation of a 3D hybrid SC electrode material with unique structural integrity and uniformity. The microstructural and chemical characterization of the hybrid electrode reveals the predominant formation of crystalline hausmannite-Mn 3 O 4 after the pyrolysis/annealing process, which is a favorable pseudocapacitive material for EES. With the combination of the 3D free-standing carbon architecture and self-assembled binder-free Mn 3 O 4 nanostructures, electrochemical capacitive charge storage with very good rate capability, gravimetric and areal capacitances (186 F g -1 and 968 mF cm -2 , respectively), and a long lifespan (>92% after 5000 cycles) is demonstrated. It is worth noting that the gravimetric capacitance value is obtained by considering the full mass of the electrode including the carbon current collector. When only the mass of the pseudocapacitive nanomaterial is considered, a capacitance value of 457 F g -1 is achieved, which is comparable to state-of-the-art Mn 3 O 4 -based SC electrode materials.