Review—Supercritical Deposition: A Powerful Technique for Synthesis of Functional Materials for Electrochemical Energy Conversion and Storage

Abstract

Supercritical fluid-based technologies are increasingly being used to develop novel functional nanostructured materials or improve the properties of existing ones. Among these, supercritical deposition (SCD) is an emerging technique to incorporate metals on supports. It has been used to deposit a wide variety of single or multi-metallic morphologies such as highly dispersed species, nanoparticles, nanorods and conformal films on high surface area supports, polymers and crystalline substrates. SCD is also attracting increasing attention for preparation of micro or nano-architectured functional materials in a highly controllable manner for electrochemical energy conversion and storage systems. Increasing number of studies in the literature demonstrates that materials synthesized using SCD are comparable or superior in performance as compared to their conventional counterparts. In this review, an overview of the fundamentals of the SCD technique is presented. Properties of a wide variety of nanostructured functional materials such as supported nanoparticles and films prepared using SCD for electrochemical applications are summarized. The electrochemical performance of these materials in electrochemical tests and also in fuel cells, electrolyzers and Li-ion batteries are also presented.

Ultra-fast single-crystal polymerization of large-sized covalent organic frameworks

“…The viscosity of sc-CO 2 is about 0.02 cp (80 °C, 8 MPa), while the surface tension is near zero 36 . The diffusion coefficient is 1–2 orders of magnitude higher than that in organic solvent 37 . As a result, sc-CO 2 allows increased penetrating ability and much faster diffusion of precursors and by-products in the medium and in the micro-pores or interstices of COFs 38 .…”

Supercritical Carbon Dioxide-Based Processes in Photocatalytic Applications

“…Metals and metal oxides can be dispersed as nanoparticles on both the external and the internal surface of support materials. Supercritical deposition has been attracting interest because of the peculiar properties of scCO 2 , such as solvent power adjustable with small variations in pressure and temperature, absence of liquid waste and solvent residue on the substrate, fast rates of deposition because of high mass transfer rates at supercritical conditions [ 58 , 59 ]. According to Watkins and McCarthy [ 60 ], it is possible to consider three subsequent steps ( Figure 1 ): The metal precursor is dissolved in scco 2 ; The metal precursor is adsorbed from the fluid phase to the support material or reacts with the surface of the support; The adsorbed metal precursor is converted to its metal or metal oxide form.…”

Synthesis and Characterization of Ni-Pt Alloy Thin Films Prepared by Supercritical Fluid Chemical Deposition Technique

“…Such materials have been the subject of intense research in the field of inorganic or organic–inorganic hybrid materials aiming to improve the physicochemical properties compared to existing materials. In addition, the materials’ characteristics and novel application opportunities depend on the fabrication method, creating the need to design and optimize new synthetic approaches [ 9 , 10 ]. For these reasons, a variety of materials processing technologies are utilized in a wide range of applications areas, including microelectronic devices, optics, energy conversion/storage, chemistry, and catalysis.…”

“…A SCF is a hybrid phase of both liquid and gas that is easily tunable with small variations in temperature or pressure. Under typical processing conditions, SCF are characterized by liquid-like density, gas-like viscosity, higher diffusivity than liquids, and zero surface tension [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ].…”

“…Moreover, by the addition of co-solvents (ethanol, acetone, hexane, isopropyl alcohol, etc.) in CO 2 , the solubility of polar precursors can be increased due to changes in polarity and density of the solvent, which makes it more attractive as a solvent medium for controlling the solubility of precursors in the processing of micro/nanomaterials [ 9 , 10 ]. One of the SCF-based technologies that has attracted interest in the development of functional materials is supercritical fluid chemical deposition (SFCD).…”