Abstract
A simple two-step electrochemical method for the fabrication of a new type of hierarchical Sn/SnOx micro/nanostructures is proposed for the very first time. Firstly, porous metallic Sn foams are grown on Sn foil via hydrogen bubble-assisted electrodeposition from an acidulated tin chloride electrolyte. As-obtained metallic foams consist of randomly distributed dendrites grown uniformly on the entire metal surface. The estimated value of pore diameter near the surface is ~35 µm, while voids with a diameter of ~15 µm appear in a deeper part of the deposit. Secondly, a layer of amorphous nanoporous tin oxide (with a pore diameter of ~60 nm) is generated on the metal surface by its anodic oxidation in an alkaline electrolyte (1 M NaOH) at the potential of 4 V for various durations. It is confirmed that if only optimal conditions are applied, the dendritic morphology of the metal foam does not change significantly, and an open-porous structure is still preserved after anodization. Such kinds of hierarchical nanoporous Sn/SnOx systems are superhydrophilic, contrary to those obtained by thermal oxidation of metal foams which are hydrophobic. Finally, the photoelectrochemical activity of the nanostructured metal/metal oxide electrodes is also presented.
Highlights
IntroductionNanoporous metal foams (metal nanofoams) are a relatively new class of materials intensively investigated by the research community [1,2]
Nanoporous metal foams are a relatively new class of materials intensively investigated by the research community [1,2]
Hydrogen bubbles arising from the reduction of H+ ions play a role of a “soft template” during the process, and because of their periodic generation and detachment, the metal foam featured with irregularly shaped voids is formed on the conductive substrate due to deposition of tin into the gaps between the attached bubbles
Summary
Nanoporous metal foams (metal nanofoams) are a relatively new class of materials intensively investigated by the research community [1,2] These three-dimensional structures built by interconnected nanoparticles and/or nanosized filaments represent a unique combination of properties typical for nanostructured (e.g., ultralow density, high porosity, and surface area [3,4]) and bulk metals (such as high thermal and electrical conductivity [1,5]). The approach allows us to obtain deposits with much higher surface area compared to a standard plain foil [10] and, in contrast to other reported methods, does not require either sophisticated equipment or complex procedures Another attractive feature of this process is the formation of hierarchically organized micro/nanostructures [11] with higher accessibility of the inner surface to external agents compared to bulk particles of nanoporous solids (as additional microstructuring should shorten the length of nanopores helping to mitigate possible diffusion limitations within them). Nanofoams of a set of metals (Cu, Ag, Pt, Pd, etc.) [11,12,13,14] and alloys [6] were obtained by electrodeposition, in particular, successful fabrication of Sn nanofoams has been reported [4,8,15]
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