A brief review on niobium oxide for supercapacitors: Unveiling fundamentals, recent breakthroughs, and promising future horizons

This review delves into the evolution and potential of niobium oxide as a supercapacitor material, addressing the critical need for sustainable energy solutions. Supercapacitors, essential for modern energy storage systems, are categorized into electrical double-layer capacitors (EDLCs) and pseudocapacitors. Niobium oxide, a promising pseudocapacitor material, offers stable cycling performance and minimal volume change during ion intercalation, though its low conductivity presents challenges that can be addressed by incorporating conductive materials or synthesizing nanostructured forms, which exhibit high specific capacitance and good stability. The review begins by establishing a robust theoretical foundation, detailing niobium oxide's various phases, crystal structures, electrical properties, and defect states. It explores how these electrochemical characteristics impact its efficiency and suitability as a supercapacitor material. The review further examines recent advancements in niobium oxide and its composites, including innovative synthesis methods and integration with other materials to enhance performance. Studies on nanostructured and nanocomposite forms of niobium oxide aim to overcome issues related to conductivity and energy density. Additionally, the review identifies gaps in the existing literature and analyzes the limitations and challenges impeding the full utilization of niobium oxide, such as material stability, synthesis scalability, and performance optimization. Finally, it outlines future research directions, including advanced material design, novel composites, and innovative testing methods, aiming to advance the development of next-generation supercapacitors leveraging niobium oxide's unique properties for improved performance and sustainability in energy storage.