Titanium Felt For Electrolyzer

(1) Using titanium sintered felt as a fuel cell gas diffusion layer, carbon fiber is easy to corrosion;

(2) Titanium sintered felt coating method including coating-baking method, pulse plating;

The minimum thickness of the titanium fiber mat is 0.25mm, the pore gap rate is 50-70%, and the structure is more conducive to gas-liquid mass transfer. In order to maintain its conductivity, the surface needs to be plated with platinum and iridium. There is the problem of a large amount of precious metal and high price; There were some problems such as poor coating stability and falling off the anode coating.

Sintered titanium felt was used as a substrate for Pt catalyst deposition. The samples used are circular, 30mm in diameter, and 1mm thick, with porosity higher than 70%. The specific processing steps are as follows:

(1) Deoxidized film: The titanium felt was prepared in an electrolytic pickling solution from Wieland Edelmetalle, Germany, based on nitric acid and hydrofluoric acid, pH 0.5 at room temperature; Then a voltage of 2.5V has been applied to the felt, causing the anodic dissolution of the Ti/Tio 2 surface. A titanium expansion net based on counter electrodes plated with platinum from Wieland Edelmetalle has been used for this purpose preparation step.

(2) Argon cleaning: After rinsing with deionized water, the titanium workpiece surface is plasma treated in argon to remove the remaining pollutants on the titanium surface. The plasma reactor was operated using PINK V 15-G from PINK Thermosysteme GmbH (Germany) and the parameters were set to an argon flow rate of 100 ml min-1, treated at 60 Pa air pressure for 30 minutes, and the microwave power was 400 W.

(3) Coating: Plasma physical cleaning process was carried out continuously and further rinsed with deionized water. Titanium fibers were immediately plated with platinum by the electrochemical method under argon. The commercially available plating bath type Galvatron Platinbad from Wieland Edelmetalle has been used based on HCH. Bath parameters were set to 8 for pH and 50 °C for temperature. The plating process was carried out for 10 min at a constant cathode voltage, -3.2V with the counter electrode (Titanium/platinum from Wieland Edelmetalle). During this electroplating process, the titanium electrode is placed electrically between two connected counter electrodes. Subsequently, in order to increase the electrochemical activity of the catalyst to deposit micrometer and nanoscale platinum particles on the surface area, the plating mode has been switched to pulse plating of the counter electrode at a cathode voltage of -3.0 V without interrupting the process. The on-time is set to 10 ms and the off time is set to 56.7 ms, so the duty cycle is 15% cycle. The second part of the plating process continues for another 10 minutes.

(4) MEA assembly: Electrodes have been impregnated with 0.5 mL Nafion® proton conducting ionomer solution (5 wt.% in ethanol) and subsequently platinized. The solution has been applied by an airbrush to the casting while a titanium-based electrode is attached to a heated sample holder. The temperature was set to 60 °C to accelerate the evaporation of ethanol from the electrode surface.

(5) and bipolar plate to form a stack, of 20 groups.

The micrographs below show the sintered titanium fibers with platinum coating. Fibers located on the outside of the feet protect the entire coating. This effect can be explained by the distribution of the electric field in the galvanic cell (the working electrode is located between and parallel to the two reverse electrodes). The coating is sufficient for stable long-term adhesion of platinum nanoparticles. Below is a micrograph of platinum particles deposited on titanium-coated fibers by the pulse electroplating process.

(1) Preparation of titanium fiber felt coating:

An Ir02 and Ru02 hybrid MMO coating was prepared on the surface of the titanium fiber mat by the method of etching, roasting, and reduction with concentrated hydrochloric acid.

The titanium fiber mat with a thickness of 0.25mm was heated in 35% HCL at 53℃ for 5 minutes to completely remove the oxide layer and improve the roughness of the fiber surface. The mat was then placed in deionized water and absolute ethanol for 5-10 minutes by ultrasonic cleaning. The total concentration of 0.03mol/L chloroiridium acid, RuC1 3, and TaCU Kunhe solution was prepared, and the coating amount was calculated according to the load of precious metal of 1 mg/cm2. The coating was applied 5-7 times. After each coating, the solution was calcined at 455℃ for 10 mi N in a Muffle furnace. Roast for 30min.

(2) Morphology analysis

There are micrometer grooves and holes on the surface of titanium fiber after hydrochloric acid corrosion, which provide more points for the combination of fiber and coating and improve the stability of the coating. With the increase of Ru content in the coating, the grain length of the coating increases gradually.

(3) Resistivity: It is close to the resistivity of the comparison platinum-plated porous sintered titanium plate. Considering that the stability of RuO2 is worse than IrO, the content of RuO2 in the layer should be strictly controlled.

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