Abstract
Nickel nanoparticles loaded on the electron–proton mixed conductor BaCe0.5Zr0.3−xY0.2NixO3−δ (Ni/BCZYN, x = 0 and 0.03) were synthesized for use in the hydrogen electrode of a proton-conducting solid oxide electrolysis cell (SOEC). The Ni nanoparticles, synthesized by an impregnation method, were from 45.8 nm to 84.1 nm in diameter, and were highly dispersed on the BCZYN. The BCZYN nanoparticles, fabricated by the flame oxide synthesis method, constructed a unique microstructure, the so-called “fused-aggregate network structure”. The BCZYN nanoparticles have capability of constructing a scaffold for the hydrogen electrode with both electronically conducting pathways and gas diffusion pathways. The catalytic activity on Ni/BCZYN (x = 0 and 0.03) catalyst layers (CLs) improved with the circumference length of the Ni nanoparticles. Moreover, the catalytic activity on the Ni/BCZYN (x = 0.03) CL was higher than that of the Ni/BCZYN (x = 0) CL. BCZYN (x = 0.03) possesses higher electronic conductivity than BCZYN (x = 0) due to the Ni doping, resulting in an enlarged effective reaction zone (ERZ). We conclude that the proton reduction reaction in the ERZ was the rate-determining step on the hydrogen electrode, and the reaction was enhanced by improving the electronic conductivity of the electron–proton mixed conductor BCZYN.
Highlights
The widespread use of hydrogen in fuel cell vehicles (FCVs) and residential use is expected to reduce CO2 generation and to lead to better distributed electric power generation
We have focused on the hydrogen electrode for the proton-conducting solid oxide electrolysis cell (SOEC)
BCZYN (x = 0 and 0.03) nanoparticle powders with a fused-aggregate network structure were prepared by the flame oxide synthesis method [35,36,37,38,39,40,41]
Summary
The widespread use of hydrogen in fuel cell vehicles (FCVs) and residential use is expected to reduce CO2 generation and to lead to better distributed electric power generation. Water vapor electrolysis by use of solid oxide electrolysis cells (SOECs) can generate high purity hydrogen, with their highest conversion efficiency at high temperature (700–900 ◦ C). The SOECs can operate reversibly as a solid oxide fuel cell (SOFC) and contribute to the leveling of electric power generation. SOECs utilizing an oxide–ion conducting electrolyte can generate high purity hydrogen at the hydrogen electrode, but it is necessary to remove a slight amount of unreacted water [1]. SOECs utilizing a proton-conducting electrolyte, can produce high purity hydrogen directly at the hydrogen electrode [2,3,4]. The proton-conducting electrolytes of the SrCeO3 and BaCeO3 systems have high conductivity, up to 0.07 S cm−1 at 800 ◦ C, which is higher than those of the SrZrO3 and
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