and widespread use. [6,7] As an alternative, metal ion batteries, including aluminum ion batteries, [8,9] sodium ion batteries, [10,11] magnesium ion batteries, [12,13] and potassium ion batteries (KIBs) [14][15][16][17][18][19][20][21][22] have aroused much interests owing to their low cost, environmental friendliness, and high energy density. Among the metal ion batteries studied, KIBs came into spotlight recently, combining the merits such as abundant resources, cost-effective, as well as the relatively low redox potential (2.92 V vs standard hydrogen electrode (SHE)). [23][24][25][26] As a new energy storage technology, KIBs have attracted worldwide attention due to their high energy density, cost-effective, good reliability, and environmental friendliness. However, it is generally known that the radius of potassium ions is as large as 0.38 nm, which will make the insertion/ extraction difficult during the electrochemical reaction, resulting in lousy capacity, bad rate performance, and short cycle lives in KIBs. [18,27] Furthermore, using additives and metal current collectors will block the active sites, slowdown the electron/ion transport, decrease the flexibility and energy density of the whole battery. In addition, the energy density, power density, as well as cycle life of KIBs are still unsatisfactory. [17,[19][20][21] Hence, development of advanced electrode materials and design of appropriate structures for KIBs are urgently desirable but remain a great challenge.In this spirit, only within the past year have studies emerged demonstrating that the potassium could form KC 8 with graphite, and undergo reversible insertion and extraction. [27][28][29][30][31] For anode electrodes, graphite appears to be one of the most promising due to their high electronic conductivity, rational potassium storage capability, and low cost. [19,22,27,[32][33][34] Although graphite has been investigated as KIBs anode and made some achievements, the rate capability and cyclic performance are still far from satisfactory, which can be attributed the large volume change of graphite and low diffusion kinetics of potassium ion during intercalation/deintercalation. [16,27] Instead, the graphene has a single or multilayer structure, which is beneficial for alkali metal ion insertion/extraction and surface storage. [22,28,31,[35][36][37][38][39] Moreover, the wrinkle structure of graphene can accommodate volume change of charge/ discharge process to retain the structure stability of materials. [40][41][42][43][44] Furthermore, by adjusting the electronic structure, active sites and interlayer With the fast development in flexible electronic technology, power supply devices with high performance, low-cost, and flexibility are becoming more and more important. Potassium ion batteries (KIBs) have a brilliant prospect for applications benefiting from high voltage, lost cost, as well as similar electrochemistry to lithium ion batteries (LIBs). Although carbon materials have been studied as KIBs anodes, their rate capability and cycling ...

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With the rapid development of portable and wearable electronics, energy storage devices featuring high energy and power densities, long-cycle lifetime, environment friendliness, safe operation, lightweight, ultrathin thickness and flexibilityl have become increasingly important.

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The exploration of efficient and cost-effective cathodes for flexible hybrid supercapacitors (HSCs) and microbial fuel cells (MFCs) is highly desirable but challenging.