Flexible All‐Solid‐State Direct Methanol Fuel Cells with High Specific Power Density

Abstract

LIBs are widely considered as an ideal flexible energy storage device due to their high energy density and long cycle life. [3] However, numerous problems remain for flexible LIBs to meet commercial LIB criteria, such as a gravimetric energy density of 250 Wh kg −1 .Direct methanol fuel cell (DMFC) is a typical and excellent model for these devices, and will serve as an intriguing candidate for the future flexible energy source due to its high energy density (4820 Wh L −1 , much greater than LIBs). The greatest power density of flexible DMFC based on the quasi-solid potassium polyacrylate hydrogel electrolyte has recently been reported to be 8.86 mW cm −2 . [13] However, progress in studies on DMFC flexibility is still sluggish, and the main causes are as follows. 1) Graphite or metal plates, which are typically too heavy, mechanical, and hard to be used with flexible electronic components, are used as flow channels and collectors in traditional DMFC. [14] 2) Due to its strong electronic conductivity, porosity that facilitates mass transfer, and great chemical stability, carbon paper is frequently utilized as a supporting layer of the membrane electrode assembly (MEA) in conventional DMFC. However, because of its mechanical rigidity, carbon paper is not appropriate for flexible DMFC. [15] 3)In order to create flexible DMFC, it is currently extremely difficult to choose and design flexible porous electrode materials with ideal mechanical properties and excellent electrical conductivity. [16] 4) Due to the usage of liquid fuel, the DMFC is orientation sensitive and fuel leakage is simple, which increases the complexity of structure and the difficulty in preparation procedure. [17] The flexible porous electrode serves as a bipolar plate in addition to its role in MEA. In current flexible devices, carbon fiber, [18] carbon nanotubes, [19] graphene, [20] carbon cloth, [21][22][23] and silver nanoparticles [19] are usually used as porous electrode materials. Although the possibilities for using carbon nanotubes, graphene, and other nanomaterials are increased by their high electrical conductivity and excellent chemical properties, it is still challenging to produce flexible electrodes in large quantities with high mechanical performance. Carbon cloth is a wellresearched material with excellent mechanical strength, flexibility, and superior electrical conductivity compared to CNT and graphene, which makes it more suitable for current collection.It is vital to create flexible batteries as power sources to suit the needs of flexible electronic devices because they are widely employed in wearable and portable electronics. The direct methanol fuel cell (DMFC) is a desirable alternative portable energy source since it is a clean, safe, and high energy density cell. The traditional DMFC in mechanical assembly and its unbending property, however, prevent it from being employed in flexible electrical devices. In this study, the flexible membrane electrode assembly (MEA) with superior electrical conductivity and nanoscale TiC-mo...