Reactive Spray Deposition Technology As an Alternative Method for Precious Metals Deposition on Sintered Titanium Porous Transport Layers for Application in Advanced Proton Exchange Membrane Water Electrolyzers

Abstract

The metal layer deposition technologies have been revolutionized throughout the years. One of the most common forms of thin metal film deposition techniques is Physical Vapor Deposition (PVD). Within the category of PVD, there are many modifications based on the source of deposition. Among all PVD variations, the Electron Beam Physical Vapor Deposition (EB-PVD) has the advantages of higher deposition rates, the ability to deposit a wide range of high purity metals for high purity films, and the creation of continuous film layers. [1,3]. EB-PVD is better known as a thermal vaporization technique. Thermal Vaporization focuses on a source, in this case an Electron Beam (EB), which bombards the desired source material with electrons. The electron beam increases the temperature of the porous metal source until it reaches its vapor phase. The metal vapor is then condensed onto the surface of the substrate holder perpendicular to the source material. While EB-PVD is known for its advantages of higher material utilization efficiency, higher deposition rates, and better step coverage [1], it lacks in its ability to penetrate into the volume of Porous Transport Layer (PTL) or coat surfaces that are not perpendicular to the source. This is important as the PTL is in contact with a corrosive environment, which causes metal corrosion and degradation of the PTL at the surfaces that are not protected by the coating.A key aspect plaguing the thin film deposition techniques is the ability to penetrate deep into the volume of a PTL and provide full coating of the porous material, including surfaces not perpendicular to the source. In an attempt to find a solution to this challenging task, we explored the capability of the Reactive Spray Deposition Technology (RSDT) to deposit precious metal nanoclusters directly onto all surfaces in the volume of the sintered titanium material [2]. The studied metal coating of interest is Gold (Au). In this work, we have deposited Au coatings of various thicknesses onto the Ti-PTLs by using both EB-PVD and RSDT techniques. The Au thin film deposits are characterized by scanning electron microscopy (SEM), digital optical microscopy, inductively coupled plasma (ICP), and focused ion beam scanning electron microscopy (FIB-SEM) [2]. The optimal deposition parameters for thin and continuous Au films with precisely controlled thicknesses have been identified. In addition, the depth of penetration of the deposits in the volume of the PTL as a function of the deposition parameters have been studied in detail, and the results will be reported at the ECS 242 meeting.