Oxygen-assisted Cathodic Deposition of Copper-Carboxylate Metal–Organic Framework Films

Abstract

Reductive deposition is an attractive strategy to prepare films of metal–organic frameworks (MOFs), but to cathodically deposit the intergrown dense films of MOFs containing readily reduced metal ions (e.g., Cu2+) without the plating of the corresponding metals still remains a significant challenge. Here, we report the cathodic deposition of metallic copper-free films of two copper-carboxylate MOFs (HKUST-1 and MOF-14). Our strategy relies on the utilization of O2 as probase to electrochemically trigger the crystallization of MOFs. Systematical cyclic voltammetry studies indicate that the favorable synergistic catalytic effects of the acidic copper ions and benzene-1,3,5-tricarboxylic acid ligands on the O2 reduction can positively shift the deposition potential of HKUST-1 significantly to +0.05 V (vs Ag/AgCl), avoiding effectively the plating of metallic copper and facilitating greatly the control over the crystallization kinetics of MOFs. By the further optimization of experimental conditions relevant to reaction temperature, supporting electrolyte, O2 concentration, and working potential, the intergrown dense MOF films with tunable thicknesses were deposited successfully on several commonly used electrodes including the highly oriented pyrolytic graphite, carbon fiber, carbon cloth, and fluorine-doped tin oxide.

Recent advances on electrochemical methods in fabricating two‐dimensional organic‐ligand‐containing frameworks

“…In addition, two kinds of copper‐carboxylate MOFs (Cu‐BTC and MOF‐14 [Cu 3 BTB 2 , H 3 BTB = benzene‐1,3,5‐tris(4‐benzoic acid)]) were also prepared without any metallic plating through the oxygen‐assisted cathodic deposition (Figure 11B). 75 The synergistic catalytic effects of the acidic copper ions and BTC ligands on the O 2 reduction can positively shift the deposition potential of Cu‐BTC significantly to +0.05 V (vs. Ag/AgCl 3 mol/L KCl), which is far positive than that of the plating of metallic copper. For the deposition of Cu‐BTC, a dimethyl sulfoxide (DMSO) solution containing 10 mmol/L of Cu(NO 3 ) 2 and 5 mmol/L of H 3 BTC was prepared due to the strong interactions between the DMSO molecules and Cu 2+ as well as the formation of hydrogen‐bonded between DMSO and H 3 BTC, which endows this precursor solution with good stability.…”

“…Thus, the undercut‐induced detachment in anodic dissolution (vide supra) can be circumvented in cathodic ECD 40 . However, the cathodic ECD needs demanding conditions, otherwise the metal plating will take place simultaneously, which results in the impurity of the as‐synthesized MOFs 70,74,75 …”

“…(C–E) SEM images of Cu‐BTC films on FTO substrate deposited at 120°C and −0.05 V for 1 h with the O 2 ‐saturated precursor solutions in the (C) presence and (B) absence of supporting electrolyte (TATFB), and with the air‐saturated precursor solutions in the (E) absence of supporting electrolyte. Reproduced with permission: Copyright 2020, American Chemical Society 75 . SEM, scanning electron microscope; ZIF, zeolitic imidazolate framework…”

Cathodic Electrodeposition of MOF Films Using Hydrogen Peroxide

“…For instance, Lu et al recently reported the reduction of dissolved molecular oxygen for the deprotonation of carboxylic ligands. [25][26] They achieved the cathodic deposition of Cu-BTC (BTC = benzene-1,3,5-tricarboxylate) in the potential range between À0.1 V and 0.05 V vs. Ag/AgCl at 120 8C by pre-purging the electrolyte with oxygen. [25] Nevertheless, the high temperature, limited solubility of oxygen in aprotic solvents, narrow working potential range and low current density (ca.…”

“…[25][26] They achieved the cathodic deposition of Cu-BTC (BTC = benzene-1,3,5-tricarboxylate) in the potential range between À0.1 V and 0.05 V vs. Ag/AgCl at 120 8C by pre-purging the electrolyte with oxygen. [25] Nevertheless, the high temperature, limited solubility of oxygen in aprotic solvents, narrow working potential range and low current density (ca. 0.03 mA cm À2 at À0.1 V vs. Ag/AgCl) due to the low solubility of oxygen in most solvents does not make this method appealing for practical deposition of MOF films.…”