Application of Thermal Spray Coatings in Electrolysers for Hydrogen Production: Advances, Challenges, and Opportunities

Abstract

Thermal spray coatings have the advantage of providing thick and functional coatings from a range of engineering materials. The associated coating processes provide good control of coating thickness, morphology, microstructure, pore size and porosity, and residual strain in the coatings through selection of suitable process parameters for any coating material of interest. This review consolidates scarce literature on thermally sprayed components which are critical and vital constituents (e.g., catalysts (anode/cathode), solid electrolyte, and transport layer, including corrosion-prone parts such as bipolar plates) of the water splitting electrolysis process for hydrogen production. The research shows that there is a gap in thermally sprayed feedstock material selection strategy as well as in addressing modelling needs that can be crucial to advancing applications exploiting their catalytic and corrosion-resistant properties to split water for hydrogen production. Due to readily scalable production enabled by thermal spray techniques, this manufacturing route bears potential to dominate the sustainable electrolyser technologies in the future. While the well-established thermal spray coating variants may have certain limitations in the manner they are currently practiced, deployment of both conventional and novel thermal spray approaches (suspension, solution, hybrid) is clearly promising for targeted development of electrolysers.

Thermal Sprayed Protective Coatings for Bipolar Plates of Hydrogen Fuel Cells and Water Electrolysis Cells

“…As mentioned in Section 2.2, high-temperature oxidation of the FSS BPs mainly occurs on the SOFC-cathode and SOEC-anode sides [86]. Although both cases are exposed to oxygen-containing gases, the latter is actually experiencing a more harsh oxidizing condition, which can be explained in two aspects: (i) A high temperature is conducive to improving the hydrogen production efficiency; therefore, the SOECs' operating temperature is usually higher than that of SOFCs, bringing more stringent technical demands on the coating stability throughout its lifespan [45]. (ii) The water vapor content in the intake of SOECs is much higher than that of SOFCs.…”

“…High-velocity oxygen fuel (HVOF) spraying is an advanced coating technology suitable for rapid preparation of dense-structured coatings of metal, alloy and ceramics without oxidizing or decomposing. The detailed processes of HOVF spraying are described as follows [43]: the fuel (such as propane, acetylene, kerosene or propylene) and high-pressure oxygen are evenly mixed and violently burned in the combustion chamber to generate a high-pressure flame, which is then accelerated into a supersonic flame stream (velocity of 400-1000 m s −1 or even higher) [45] through the Laval nozzle. The supersonic flame accelerates and heats the feedstock materials fed into this flame to be of a molten or semimolten state.…”

“…Unlike APS and VPS, HVOF uses a high-temperature flame originating from the combustion of fuel (e.g., propane, acetylene, kerosene or propylene) to melt down the coating materials. The characteristics of these technologies are shown in Figure 2c [45]. Due to significant differences in the atmosphere, flame temperature and flame speed among these three spraying technologies, the appropriate coating materials for spraying vary significantly as well.…”

“…The effect of spraying parameters on detailed coating composition and microstructure, as well as the corrosion resistance and electrical conductance, are reviewed for the individual thermal spraying technologies. [43]; classification of the thermal spraying technologies (b) [44]; particle temperature and velocity characteristics of APS, VPS and HVOF (c) [45]; actual photographs and spraying mechanisms (inset maps) of APS (d), VPS (e) and HVOF (f); various bipolar plates used in SOFCs (g), SOECs (h), PEMFCs (i) and PEMECs (j).…”

“…Figure 2. Deposition principle (a) of thermal spraying[43]; classification of the thermal spraying technologies (b)[44]; particle temperature and velocity characteristics of APS, VPS and HVOF (c)[45]; actual photographs and spraying mechanisms (inset maps) of APS (d), VPS (e) and HVOF (f); various bipolar plates used in SOFCs (g), SOECs (h), PEMFCs (i) and PEMECs (j).…”