Performance of Ni/YSZ cermet cathode prepared by mechanical alloying for high temperature electrolysis of water vapor (steam): effect of anode and cathode thicknesses on the efficiency of hydrogen production

摘要

Ni/YSZ (Y{sub}2O{sub}3-stabilized ZrO{sub}2) composite cathode is fabricated by high-nergy ball milling of Ni and YSZ powders for high temperature electrolysis of water vapor. Composite powder composition, time and rotation speed of ball milling were optimized by trial and error for suitable performance with maximum efficiency of fabricated cathode in high temperature electrolysis of water vapor (steam) at 800 ℃. The composite powders thus synthesized were characterized using various analytical tools such as X-ray diffraction, scanning electron microscopy and particle size analysis, and a self-supporting planar type unit cell was prepared with Ni/YSZ composite cathode and Pt paste anode screen-printed on each side of YSZ electrolyte disk (30 mm dia.) and then sintered at 1450 ℃ for high temperature electrolysis. X-ray diffraction and particle size analysis results showed that the Ni/YSZ composite effectively consisted of crystalline Ni and YSZ distributed on a sub-micron scale and evenly distributed without aggregation of particles. To study the effect of anode and cathode thickness on the efficiency of the hydrogen production rate, screen-printing of anode and cathode was carried out on each side of YSZ electrolyte to three different thickness values during the fabrication of a self-supporting planar type unit cell which operated quite satisfactorily during high temperature electrolysis at 800 ℃: a significantly higher hydrogen production rate of 13 seem (standard cubic centimeters per minute) was reproducibly observed for triple screen-printing of anode and cathode over each side of the YSZ electrolyte disk compared to 0.5 seem for the single screen-printed cathode under an applied direct current of 0.7 mA cm{sup}(-2). Additionally, linear increase in hydrogen production was observed with applied current for triple screen-printed electrodes in contrast to single and double screen-printed electrodes.