Microfluidic Printing of Vertically‐Oriented Nanosheets/MOFs Hetero‐Interface for Intensive Pseudocapacitive Storage

Abstract

Efficient manufacture of electroactive vertically‐oriented nanosheets with enhanced electrolyte mass diffusion and strong interfacial redox dynamics is critical for realizing high energy density of miniature supercapacitor (SC), but still challenging. Herein, microfluidic droplet printing is developed to controllably construct vertically‐oriented graphene/ZIF‐67 hetero‐microsphere (VAGS/ZIF‐67), where the ZIF‐67 is coordinately grown on vertically‐oriented graphene framework via Co─O─C bonds. The VAGS/ZIF‐67 shows ordered porous channel, high electroactivity and strong interfacial interaction, providing rapid electrolyte diffusion dynamics and high faradaic capacitance in KOH solution (1674 F g−1, 1004 C g−1), which are verified by computational fluid dynamics (CFD) and density functional theory (DFT). Moreover, the VAGS/ZIF‐67 based SC exhibits large energy density (100 Wh kg−1), excellent durability (10 000 cycles and high/low temperature), and robust power‐supply applications in portable electronics.

Microfluidic Synthesis of Multifunctional Micro-/Nanomaterials from Process Intensification: Structural Engineering to High Electrochemical Energy Storage

“…To further confirm the formation mechanism of the vertically aligned structure, Yu et al proposed computational fluid dynamics (CFD) simulations to analyze the specific velocity field and force field of the contracted−expanded microchannel. 53 Generally, the contracted microchannel mainly provided a shear flow with strong shear stress. The shear stress would drive graphene nanosheets to be arranged horizontally along the radial direction of the contracted microchannel.…”

“…At the beginning, the radial normal stress between materials building blocks is larger than the axial normal stress. The larger radial normal stress will persistently provide strong rotational torque to drive materials building blocks from horizontal to vertical arrangement until reaching mechanical equilibrium, and therefore, the vertically aligned structure is easily achieved. , Furthermore, multiphase fluid manipulation is an essential influence factor for the formation of the core–shell structure. By designing the tube-in-tube-type and slit-type microchannel configurations, the double aqueous phase fluids of core fluid and shell fluid with various fluid velocities, fluid viscosities and surface tensions can be precisely regulated, respectively. ,, After in situ interfacial coupling reaction or chemical cross-linking, the core–shell structure with strong interfacial interaction, tunable shell thickness and uniform surface topography is constructed by microfluidic technology. , Similar to the core–shell structure, the formation of a spherical structure also involves the design of tube-in-tube-type microchannel configurations and multiphase fluid manipulation.…”

“…Benefiting from the ordered orientation, the vertically aligned graphene showed an ordered diffusion channel and ultrahigh electrical conductivity of 0.8 × 10 6 S m –1 , which could greatly promote the electron conduction and ion dynamic diffusion for excellent energy storage capacity and cycling durability. To further confirm the formation mechanism of the vertically aligned structure, Yu et al proposed computational fluid dynamics (CFD) simulations to analyze the specific velocity field and force field of the contracted–expanded microchannel . Generally, the contracted microchannel mainly provided a shear flow with strong shear stress.…”

“…(a) Microfluidic construction of vertically aligned graphene/ZIF-67 . Reprinted with permission from ref . Copyright 2023, Wiley-VCH.…”