Cellulose Nanofiber @ Conductive Metal–Organic Frameworks for High-Performance Flexible Supercapacitors

Abstract

Conductive metal–organic frameworks (c-MOFs) show great potential in electrochemical energy storage thanks to their high electrical conductivity and highly accessible surface areas. However, there are significant challenges in processing c-MOFs for practical applications. Here, we report on the fabrication of c-MOF nanolayers on cellulose nanofibers (CNFs) with formation of nanofibrillar CNF@c-MOF by interfacial synthesis, in which CNFs serve as substrates for growth of c-MOF nanolayers. The obtained hybrid nanofibers of CNF@c-MOF can be easily assembled into freestanding nanopapers, demonstrating high electrical conductivity of up to 100 S cm–1, hierarchical micromesoporosity, and excellent mechanical properties. Given these advantages, the nanopapers are tested as electrodes in a flexible and foldable supercapacitor. The high conductivity and hierarchical porous structure of the electrodes endow fast charge transfer and efficient electrolyte transport, respectively. Furthermore, the assembled supercapacitor shows extremely high cycle stability with capacitance retentions of >99% after 10000 continuous charge–discharge cycles. This work provides a pathway to develop flexible energy storage devices based on sustainable cellulose and MOFs.

Recent advances in process engineering and upcoming applications of metal–organic frameworks

“…Furthermore, compositing can enhance the flexibility of the device for utilization in practical applications such as wearable electronic devices. With this in mind, two MOF composites with conductive Ni-based nanolayers grown on cellulose nanofibers (denoted as CNF@Ni-HITP and CNF@Ni-HHTP) were prepared for supercapacitor electrode applications [386] . Analysis of their electrochemical properties revealed that the asymmetric electrodes achieved a gravimetric capacitance of 125 F g −1 for CNF@Ni-HITP and 75 F g −1 for CNF@Ni-HHTP at current densities of 0.33 and 0.2 A g −1 , respectively.…”

Conductive Metal–Organic Frameworks with Extra Metallic Sites as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction

“…The theoretical and experimental investigations have demonstrated that the metal atoms in the M–N 4 linkages still remain the original oxidation state during the electrocatalytic process, which hardly shows effective activity for electrocatalysis. [ 18 ] At present, hexaiminotriphenylene (HITP, Scheme S1, Supporting Information) and/or its analogs are usually employed as the conjugated organic ligands for conductive MOFs, [ 19–22 ] which barely provide other coordinated sites to be high active metal center for electrocatalysis. Thus, designing new conjugated organic ligand with extra coordinated sites to incorporate effective active centers should be the primary priority for improving electrocatalytic performance of conductive MOFs.…”

Elastic Aerogels of Cellulose Nanofibers@Metal–Organic Frameworks for Thermal Insulation and Fire Retardancy

“…There are several advantages in developing CNF-based composites as thermal insulation materials: (1) The naturally abundant and biodegradable CNFs offer a low-cost, sustainable source of materials for manufacturing; (2) CNFs exhibit intrinsically low thermal conductivity; (3) the nanofibrous structure of CNFs results in large interfacial surface areas which act as phonon barriers with potential to hamper heat conduction; (4) CNFs containing organic functional groups on the surface are ideal substrates for modification or hybridization through surface nanoengineering, offering opportunities to overcome the longstanding problems of moisture sensitivity, flammability, and poor mechanical properties associated with CNF-based materials. We have recently developed a range of hybrid nanocomposites based on CNFs for use in energy and environmental applications [12,[34][35][36][37][38][39]. In this study, we describe the interfacial synthesis and stepwise assembly approach for the design of a hybrid aerogel based on CNFs and an aluminum-based MOF (CNF@ Al-MIL-53; CAM).…”