Synergistic Thermal Activation and Plasma for Universal Low-Temperature Synthesis of Mesoporous Metal Oxides

Mesoporous metal oxides (MMOs) with interconnected mesopores (2–50 nm) are critically important for applications in catalysis, energy storage, and sensing, owing to their substantial surface area and pore volume. This study introduces a novel and universal method for synthesizing MMOs through the co-assembly of block copolymers (BCPs) and metal oxide (MO) precursors, followed by their conversion to MMOs at reduced temperatures (150–200 °C) utilizing a synergistic thermal activation and oxygen plasma (TAP) process.<br/><br/>The BCPs serve dual roles as structure-directing agents for the self-assembly of sol-gel precursors into mesoscale architectures and as templates that sustain the resultant mesostructures. However, complete precursor condensation and BCP template removal typically require high temperatures (&gt;350 °C), which are unsuitable for flexible substrates and can damage the mesoscale structure of certain MOs (e.g., V₂O₅ and MoO₃) with rapid crystallization kinetics. The TAP process circumvents these issues by enabling complete template removal and MO formation at significantly lower temperatures, thus making it compatible with flexible substrates. In this approach, BCPs function dually as structure-directing agents for the self-assembly of sol-gel precursors into mesoscale architectures and as templates that sustain the resultant mesostructures. However, complete precursor condensation and BCP template removal typically require high temperatures (&gt;350 °C), which are unsuitable for flexible substrates and can damage the mesoscale structure of certain MOs (e.g., V₂O₅ and MoO₃) with rapid crystallization kinetics. The TAP process mitigates these issues by enabling complete template removal and MO formation at significantly lower temperatures, thereby making it compatible with flexible substrates.<br/><br/>Using vanadium pentoxide (V₂O₅) as a representative material, we successfully fabricated mesoporous V₂O₅ via the TAP process. This mesoporous V₂O₅, when utilized as an electrode material for a micro-supercapacitor (MSC), demonstrated superior electrochemical performance compared to V₂O₅ synthesized at higher temperatures (350 °C). This enhancement is attributed to its highly interconnected mesoporous structure, which provides a substantial surface area. Additionally, we achieved the direct synthesis of mesoporous V₂O₅ on indium-tin oxide (ITO) coated colorless polyimide (CPI) film, resulting in a flexible MSC that retained its energy storage performance under rigorous bending conditions (bending radius down to 1.5 cm and up to 3000 cycles). Remarkably, the TAP method was also successfully applied to synthesize a diverse array of MMOs, including V₆O₁₃, TiO₂, Nb₂O₅, WO₃, and MoO₃, at reduced temperatures. This underscores the versatility and potential of this approach for flexible device applications. This universal low-temperature synthesis technique represents a significant advancement in MMO synthesis, facilitating their direct application on flexible substrates and paving the way for the development of high-performance, flexible energy storage devices.<br/><br/>Acknowledgements:<br/>This work was supported by the National Creative Research Initiative Program supported by the National Research Foundation of Korea (NRF) grant (no. 2022R1A3A3002149) funded by the Korean government. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2022R1A6A3A13063381). This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2022R1A2C4001425).