Electrodeposited metal-organic framework films as self-assembled hierarchically superstructured supports for stable omniphobic surface coatings

Superhierarchically rough films are rapidly synthesised on metal substrates via electrochemically triggered self-assembly of meso/macroporous-structured metal-organic framework (MOF) crystals. These coatings are applied to immobilise a functional oil with low surface energy to provide stable coatings repellent to a wide range of hydrophobic as well as hydrophilic fluids. Such omniphobic surfaces are highly interesting for several applications such as anti-fouling, anti-icing, and dropwise condensation, and become easily scalable with the presented bottom-up fabrication approach. As investigated by environmental scanning electron microscopy (ESEM), the presented perfluorinated oil-infused Cu-BTC coating constitutes of a flat liquid-covered surface with protruding edges of octahedral superstructured MOF crystals. Water and non-polar diiodomethane droplets form considerably high contact angles and even low-surface-tension fluids, e.g. acetone, form droplets on the infused coating. The repellent properties towards the test fluids do not change upon extended water spraying in contrast to oil-infused porous copper oxide or native copper surfaces. It is discussed in detail, how the presented electrodeposited MOF films grow and provide a proficient surface morphology to stabilise the functional oil film due to hemiwicking.


Sample
Scan length (mm)

Raman spectroscopy
The Raman spectrum of anodised copper foil ( Supplementary Fig. 3a) contains the characteristic bands for cuprous oxide (Cu2O) which are assigned in Supplementary Table 2. The features at 413 cm -1 and 710 cm -1 have been observed for Cu2O films before 1 . The weak vibration signal around 305 cm -1 indicates the presence of cupric oxide (CuO). The CuO signal around 640 cm -1 , which was also observed for the native Cu foil ( Supplementary Fig. 3b, Table 3 Band (cm -1 ) Assignment 141 Out-of-phase beating of two Cu pairs 213 Rotation of the Cu tetrahedron about its centre with the upper two atoms moving out of phase with the lower two 520 Shearing of O planes (T2g symmetry) 630 Beating of the Cu and O sublattices Supplementary  Fig. 3) are assigned to zone-center (Γ) phonon modes in CuO (space group C2/c, 4 molecules in the unit cell) according to references 2, 3 .
Band (cm -1 ) Assignment 305 Motion of oxygen atoms with displacements in the b-direction (Ag symmetry) 640 Motion of oxygen atoms with displacements perpendicular to the b-axis (Bg symmetry)

Droplet Sinking on oil-infused samples
Visible sinking of a droplet is observed after ca. 30 seconds on the oil-infused surfaces.

Materials: Copper foil
The Copper foil produced in-house by rolling and annealing of electrolytic copper were subjected to elemental analysis, energy dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD) measurements to characterise the purity of the foil and the foil surface.

Elemental analysis
Two samples of the Cu foil (50 mg each) were dissolved in either 5 ml of a 1:1 (v/v) HNO3/H2O solution or 5 ml of a 5:5:1 (v/v/v) HNO3/H2O/HF solution to determine the content of possible contamination elements by inductively coupled plasma optical emission spectrometry (ICP-OES) using a Thermo Scientifc IRIS Intrepid II XUV. The digestion solutions were filled up with water until 50 g were reached. None of the following elements was detected: Ag, Al, B, Be, Ca, Co, Cr, Fe, K, Li, Mg, Mn, Na, Ni, Pb and Zn (detection limit < 10 ppm mass fraction in the solid).

EDXS
According to the EDXS analysis, there may be a very low amount of iron contamination on the surface of the Cu foil (Supplementary Table 4 and Supplementary Fig. 7) which (if present) was assumingly introduced during the rolling process. The energy dispersive X-Ray spectrometer Bruker XFlash Detector 4010 was connected to a FEG Gemini Leo 1530 scanning electron microscope from Zeiss.

XRD
XRD on a piece of copper foil in a wider 2θ range (5 ° ≤ 2θ ≤ 88 °) reveals signals assigned to Cu2O Pn-3m and CuO C2/c ( Supplementary Fig. 8). The signals at 48.3 ° 2θ and 53.4 ° 2θ may be due to contaminations on the surface caused by the rolling process. The measurements were conducted in reflection mode with a Philips 1050 Diffractometer using Co Kα radiation (λ = 1.790307 Å). The 2θ ranges of 50.5 ° ≤ 2θ ≤ 52 ° and 59 ° ≤ 2θ ≤ 60.5 ° were omitted during the XRD measurement as the signals of copper (bulk of the foil) appear in these ranges with very high intensities under the measurement conditions chosen to be able to observe signals of the foil surface (step size: 0.0130 ° 2θ, counting time: 248.37 s, aperture opening: 10 mm).