Ling Cao’s research while affiliated with Hunan Normal University and other places

Electrochemical fabrication of micro/nanostructured metallic surfaces with superhydrophobicity has recently aroused great attention. However, the origin still remains unclear why smooth hydrophilic metal surfaces become superhydrophobic by making micro/nanostructures without additional surface modifications. In this work, several superhydrophobic micro/nanostructured metal surfaces were prepared by a facile one-step electrodeposition process, including non-noble and noble metals such as copper, nickel, cadmium, zinc, gold, and palladium with (e.g. Cu) or without (e.g. Au) surface oxide films. We demonstrated by SEM and XPS that both hierarchical micro/nanostructures and spontaneous adsorption of airborne hydrocarbons endowed these surfaces with excellent superhydrophobicity. We revealed by XPS that the adsorption of airborne hydrocarbons at the Ar+-etched clean Au surface was rather quick, such that organic contamination can hardly be prevented in practical operation of surface wetting investigation. We also confirmed by XPS that ultraviolet-O3 treatment of the superhydrophobic metal surfaces did not remove the adsorbed hydrocarbons completely, but mainly oxidized them into hydrophilic oxygen-containing organic substances. We hope our findings here shed new light on deeper understanding of superhydrophobicity for micro/nanostructured metal surfaces with and without surface oxide films.

Superhydrophobic metallic surfaces are attracting wide interest. In this work, two facile one-step methods (displacement reaction and electrodeposition) were developed to fabricate superhydrophobic Bi/Bi2O3 surfaces with hierarchical porous dendritic structures, where the Bi2O3 cover layer was formed by surface self-passivation of the deposited Bi. The influence of various experimental parameters on the surface morphology and wettability were investigated in detail, including concentration of solutions, deposition times, and deposition potentials. A maximum contact angle about 164° can be obtained on the fabricated superhydrophobic Bi/Bi2O3 surfaces by these two methods under optimized conditions without additional surface modification.

Superhydrophobic Sn/SnOx (x = 1 and 2) films were facilely fabricated by surface self-passivation of three-dimensional (3D) hierarchical porous dendritic Sn while exposed to the air. The porous dendritic Sn was obtained rapidly by electrodeposition accompanying release of hydrogen bubbles. Influence of electrodeposition parameters on the surface morphology and wettabillity has been investigated in detail, including deposition potentials, deposition times and electrolyte concentrations. The maximum contact angle reached to 165 degrees on the porous dendritic Sn/SnOx film electrodeposited in a solution of 60 mM SnCl2 and 1.5 M H2SO4 under -1.7 V for 20 s. Both the hierarchical micro-nanostructures and the spontaneously formed ultrathin surface passivation layer of Sn oxides endow the prepared Sn/SnOx surface with excellent inherent superhydrophobicity without further surface modification.

In this communication, we report an unusual observation on vigorous gas release of H2 and CO2 from rapid auto-decomposition of formic acid at room temperature on nanodendritic AuPd and AgPd foam films. These new binary noble metal foams were prepared by electrodeposition under strongly cathodic polarization. The high catalytic activity was contributed to the abundant active sites such as steps, corners, kinks, edges and atomic dislocations in the nanodendrites comprised of nanoparticles, as well as to the electronic effect of binary metals.

Facile preparation of superhydrophobic surfaces of stable and cheap metals is practically important. We report here our findings on fabrication of a superhydrophobic metal Sn surface, which can be obtained at room temperature in 5 min through a displacement reaction between a zinc plate and an acidic SnCl2 solution without needing post-treatment and surface modification. This procedure is facile, time-saving and inexpensive, which is superior to other known displacement depositions of Pt, Ag, Au, or Cu. The effects of preparation conditions on the surface morphology and wettability have been investigated in detail, including reactant concentration and reaction time. It has been observed that superhydrophobicity was closely related with the morphological transition from tin nanoparticles/nanopores to tin dendrites, and the maximal water contact angle (CA) was about 156° with the Cassie state. We expect that this fabrication technique will find practical applications.

PtPd alloy foam films comprised of nanodendrites have been firstly fabricated by a strategy of cathodic co-deposition utilizing hydrogen bubble dynamic templates. The deposition conditions like potential, deposition time, H2SO4 concentration, precursor concentrations were investigated in detail. We found that Pd played the predominant role in the formation of alloy foams and nanodendrites in comparison with respective electrodeposition of Pd and Pt. The porous films were characterized by scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy. The PtPd alloy porous films comprised of nanodendrites showed enhanced electrocatalytic activities toward the electrooxidation of methanol and ethanol in acidic solution.

AuPt alloy films with three-dimensional (3D) hierarchical pores consisting of interconnected dendrite walls were successfully fabricated by a strategy of cathodic codeposition utilizing the hydrogen bubble dynamic template. The foam films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Due to the special porous structure, the electronic property, and the assembly effect, the AuPt alloy foam films show superior electrocatalytic activity toward the electrooxidation of formic acid in acidic solution, and the prepared 3D porous AuPt alloy films also show high activity and long stability for the electrocatalytic oxidation of methanol, where synergistic effect plays an important role in addition to the electronic effect and assembly effect. These findings provide more insights into the AuPt bimetallic nanomaterials for electrocatalytic applications.