Abstract
Titanium porous transport layers (PTL) are important components in proton exchange membrane water electrolysis (PEMWE) cells. The performance enhancement and the reduction of manufacturing cost of PTLs are of importance for market expansion of PEMWE. Vacuum plasma spraying (VPS) was used to prepare PTL or modify PTL of sintered titanium powders and the PTLs by VPS showed a high performance. Regarding the cost efficiency, it is of great interest to produce PTLs using more economical spray processes than VPS. In this study, high velocity oxy-fuel spraying (HVOF) was used to produce highly porous titanium coatings for this purpose. The spray process was developed to achieve a high porosity of up to Φ = 30 % using three titanium powders with size distributions of fA = -90 +45 μm, fB = -63 +20 μm and fc = -45 +11 μm. The coating structures were examined on the cross sections of the titanium coatings with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The porosity was determined using the image analysis system ImageJ. The deposition efficiency of the titanium powder fC = -45 +11 μm was determined. The results show that the coating structure significantly depends on the titanium powders. Highly porous titanium coatings of Φ = 24 - 40 % can be produced with the titanium powders of fB = -63 +20 μm and fc = -45 +11 μm. Titanium oxides are hardly visible on the cross-sections of the titanium coatings. A high deposition efficiency of approximately DP ≈ 70 % was measured for the titanium powder of fc = -45 +11 μm.
