Covalent organic frameworks (COFs) with redox-active units are a class of ideal materials for electrochemical-energy-storage devices. A novel two-dimensional (2D) PDC–MA–COF with redox-active triazine units was prepared via aldehyde–amine condensation reaction by using 1,4-piperazinedicarboxaldehyde (PDC) and melamine (MA) as structural units, which possessed high specific surface area (S BET = 748.2 m2 g–1), narrow pore width (1.9 nm), large pore volume (1.21 cm3 g–1), and high nitrogen content (47.87%), for pseudocapacitance application. The interlayer C–H···N hydrogen bonding can “lock” the relative distance between two adjacent layers to avoid an interlayer slip, which is more conducive to maintaining the ordered pore structure of the COF and improving a fast charge transfer between the electrode interface and triazine units. The PDC–MA–COF exhibited an excellent electrochemical performance with the highest specific capacitance of 335 F g–1 along with 19.71% accessibility of the redox-active triazine units in a three-electrode system and 94 F g–1 in a two-electrode system at 1.0 A g–1 current density. Asymmetric supercapacitor of PDC–MA–COF//AC assembled using PDC–MA–COF and activated carbon (AC) as positive and negative electrode materials, respectively, exhibited a high energy density of 29.2 W h kg–1 with a power density of 750 W kg–1. At the same time, it also showed an excellent cyclic stability and could retain 88% of the initial capacitance after 20 000 charge–discharge cycles, which was better than those of the most of the analogous materials reported previously. This study provided a new strategy for designing redox-active COFs for pseudocapacitive storage.

Covalent organic frameworks (COFs) are a new class of porous organic materials, which are constructed with periodic organic units comprised entirely of light elements (typically C, H, O, N and B) and linked by strong covalent bonds. COFs have been applied in extensive fields, owing to their extraordinary properties in areas such as gas storage and separation, heterogeneous catalysis, sensors, semiconductors, drug delivery, and photoconduction. In particular, the ordered micropore or mesopore structures, high surface areas, and designable structures have enabled COFs to become new candidates for supercapacitor electrode materials. This Minireview focuses on the major progress of COFs as electrode materials for supercapacitors.

In the present work, a novel and selective electrochemical sensor based on copper porphyrin metal organic frameworks (Cu-MOFs) and Au@Ag core-shell nanoparticles decorated multiwalled carbon nanotubes (MWCNT) was designed for the simultaneous determination of acetaminophen (ACOP) and dopamine (DA). The fabrication strategy was accomplished via drop casting of MWCNT-Au@Ag onto the bare glassy carbon electrode (GCE) and then electrodeposition of Cu-MOF on the MWCNT-Au@Ag/GCE. By combining the high surface area (400.54 m 2 •g −1 ) of Cu-MOFs with superior conductivity and electrocatalytic properties of MWCNT-Au@Ag nanocomposites, the proposed sensor exhibited the remarkable performance for the electrocatalytic detection ACOP and DA. Under the optimized conditions, Cu-MOFs/MWCNT-Au@Ag/GCE delivered good differential pulse voltammetric response in the ACOP concentration of 1.0∼40, 40∼500 μM and the DA concentration of 0.6∼70, 70∼300 μM with the detection limit of 0.232 μM for ACOP and 0.082 μM for DA, separately. In addition, the designed electrochemical sensor was applied for the determination of ACOP and DA in real samples with reliable and satisfying recoveries (97.88∼104.38% for ACOP and 98.28∼104.40% for DA, respectively) and precisions (2.15∼4.78% of RSD for ACOP and 1.47∼4.46% of RSD for DA, respectively). As expected, these data suggested that the Cu-MOFs/MWCNT-Au@Ag was an excellent potential platform for simple and convenient determination of ACOP and DA.

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