Metal-organic frameworks (MOFs) have received increasing attention as promising electrode materials in supercapacitors (SCs). Yet poor conductivity in most MOFs largely thwarts their capacitance and/or rate performance. In this work, an effective strategy was developed to reduce the bulk electric resistance of MOFs by interweaving MOF crystals with polyaniline (PANI) chains that are electrochemically deposited on MOFs. Specifically we synthesized cobalt-based MOF crystals (ZIF-67) onto carbon cloth (CC) and further electrically deposited PANI to give a flexible conductive porous electrode (noted as PANI-ZIF-67-CC) without altering the underlying structure of the MOF. Electrochemical studies showed that the PANI-ZIF-67-CC exhibits an extraordinary areal capacitance of 2146 mF cm(-2) at 10 mV s(-1). A symmetric flexible solid-state supercapacitor was also assembled and tested. This strategy may shed light on designing new MOF-based supercapacitors and other electrochemical devices.
Multivariate metal-organic frameworks with active Fe/Ni building blocks that are spatially arranged in an open structure are synthesized and explored for oxygen evolution reaction. The heterogeneity and porosity of this system prove to show synergy effect and give low onset overpotential at 170 mV. These MOFs are further fabricated into thin films over nickel foam by controlled electrochemical deposition to improve the surface conductivity and the overall stability. The Fe/Ni metal-organic framework film exhibits outstanding electrocatalytic activity with low overpotential of 270 mV at 10 mA cm(-2), small Tafel slope, high Faradaic efficiency, high turnover frequency, and great stability.
Photocatalytic nitrogen fixation
reaction can harvest the solar
energy to convert the abundant but inert N2 into NH3. Here, utilizing metal–organic framework (MOF) membranes
as the ideal assembly of nanoreactors to disperse and confine gold
nanoparticles (AuNPs), we realize the direct plasmonic photocatalytic
nitrogen fixation under ambient conditions. Upon visible irradiation,
the hot electrons generated on the AuNPs can be directly injected
into the N2 molecules adsorbed on Au surfaces. Such N2 molecules can be additionally activated by the strong but
evanescently localized surface plasmon resonance field, resulting
in a supralinear intensity dependence of the ammonia evolution rate
with much higher apparent quantum efficiency and lower apparent activation
energy under stronger irradiation. Moreover, the gas-permeable Au@MOF
membranes, consisting of numerous interconnected nanoreactors, can
ensure the dispersity and stability of AuNPs, further facilitate the
mass transfer of N2 molecules and (hydrated) protons, and
boost the plasmonic photocatalytic reactions at the designed gas–membrane–solution
interface. As a result, an ammonia evolution rate of 18.9 mmol gAu
–1 h–1 was achieved under
visible light (>400 nm, 100 mW cm–2) with an
apparent
quantum efficiency of 1.54% at 520 nm.
The production of hydrogen through electrolysis is considered as a feasible strategy to quench the world's clean-energy thirst. Compared with water electrolysis, urea electrolysis presents a more promising prospect in the way that it could carry out sewage treatment as well as energy-efficient hydrogen production at the same time. Herein, highly porous pomegranate-like Ni/C was synthesized from multivariate metal-organic frameworks and exhibits excellent hydrogen evolution activity with an unprecedented low overpotential of 40 mV at the current density of 10 mA cm in 1 M KOH, ranking among the best earth-abundant electrocatalysts deposited on glassy carbon electrodes reported to date. In addition, it also displays superb anodic urea oxidation activity with an onset potential of 1.33 V vs RHE. Furthermore, a two-electrode urea electrolyzer with Ni/C as both the cathode and anode electrocatalyst was fabricated and generates 52 times more hydrogen than the water electrolyzer under the same conditions.
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