Advancing the future: a mini review of developments and prospects in potassium-ion capacitors and potassium-ion hybrid capacitors

This review examines the advancements and challenges in potassium-ion hybrid capacitors (K-HyCs) and potassium-ion capacitors (K-ICs), emerging next-generation energy storage technologies that synergize the high energy density of batteries with the superior power density and extended cycle life of supercapacitors. These systems capitalize on potassium's natural abundance, economic viability, and advantageous electrochemical properties, presenting themselves as sustainable alternatives to lithium-based storage systems. The paper highlights recent progress in developing carbon-based anode materials, focusing on strategies such as heteroatom doping, hierarchical structuring, and using biomass-derived precursors. In addition to carbon-based materials, we also briefly discussed transition metal chalcogenide materials and titanium-based materials. These innovations are pivotal in addressing critical challenges associated with potassium's large ionic radius, which impairs ion diffusion kinetics and electrode structural stability. Furthermore, advanced electrolyte designs are discussed for their critical role in enhancing these devices' electrochemical performance and stability. Despite substantial advancements, significant obstacles remain. Key challenges include ensuring compatibility between electrode materials, achieving thermodynamic stability, and developing efficient ion transport mechanisms. Future research directions are proposed to overcome these limitations, including developing hybrid nanostructured electrodes, exploring novel electrolyte chemistries, and integrating machine learning techniques to accelerate material discovery and optimization. These efforts aim to unlock the full potential of PIHCs and PICs for scalable energy storage applications.