In-situ synthesis of mixed-valence manganese oxide@S, P self-codoped carbon@reduced graphene oxide composites by enhanced surface interaction for high-performance all-solid-state supercapacitors

By enhancing surface interaction between metal oxide particles and carbon-based materials, it can effectively improve Faraday capacitance and conductivity, ultimately achieving high energy density with sufficient redox reactions in supercapacitors. Through a gentle biomineralization process and subsequent thermal reduction strategy, we successfully prepared the graphene oxide (GO) wrapping mixed-valence manganese oxides (MnO_x) and S, P self-codoped carbon matrix porous composite (MnO_x@SPC@reduced graphene oxide (RGO)). During the biomineralization process of engineered Pseudomonas sp. (M1) cells, GO nanosheets functioned as the ‘soil’ to adsorb Mn²⁺ ion and uniformly disperse biogenic Mn oxides (BMO). After undergoing annealing, the MnO_x nanoparticles were evenly wrapped with graphene, resulting in the creation of the MnO_x@SPC@RGO3 composite. This composite possesses strong C—O—Mn bond interfaces, numerous electroactive sites, and a uniform pore structure. By optimizing the synergistic interaction between the highly conductive graphene and the remarkable surface capacitance of MnO_x, the MnO_x@SPC@RGO3 electrode, with its intercalation Faraday reactions mechanism of Mn²⁺ ⇌ Mn³⁺ and Mn³⁺ ⇌ Mn⁴⁺ transformations, exhibits an outstanding specific capacity (448.3 F·g⁻¹ at 0.5 A·g⁻¹), multiplying performance (340.5 F·g⁻¹ at 10 A·g⁻¹), and cycling stability (93.8% retention after 5000 cycles). Moreover, the asymmetric all-solid-state supercapacitors of MnO_x@SPC@RGO3//PC exhibit an exceptional energy density of 64.8 W·h·kg⁻¹ and power density of 350 W kg⁻¹, as well as a long lifespan with capacitance retention of 92.5% after 10000 cycles. In conclusion, the synthetic route utilizing biomineralization and thermal reduction exhibits significant potential for exploiting high-performance electrode materials in all-solid-state supercapacitor applications.