Experimental Study of the Electric Efficiency and Current Leakage with Bzyb Based Protonic Ceramic Fuel Cell
Authors: Yamauchi Kosuke , Mikami Yuichi , Kuroha Tomohiro , Okuyama Yuji 
Published: December 2024

Protonic Ceramic Fuel Cell (PCFC) is expected to be the next-generation fuel cell for its higher energy conversion efficiency and lower operating temperature. BaZrO3 based oxide are potential materials as PCFC electrolyte because they have high chemical stability under the CO2 conditions and high proton conductivity. In the NEDO of Japan project started from FY2020, we have developed to demonstrate operation at high fuel utilization and to improve durability. In the previous report, we evaluated the electric efficiency using a Φ60mm anode supported PCFC and investigated the effect of the fuel utilization on the terminal voltage by controlling the supply of the hydrogen to the anode gas. Then, we demonstrated that a BaZr0.8Yb0.2O3-
δ (BZYb） based PCFC could be operated at a high Uf condition (i.e., Uf = 90%), and the maximum electric efficiency was 55% (DC).

In this study, we compared the power generation efficiency between the cell with BZYb single-layered electrolyte and the cell with BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb)/ BZYb double-layered electrolyte.

Φ60mm anode supported PCFC was fabricated by tape-casting process used for the industrial production of ceramic electronic devices. NiO-BZYb anode slurry, BZYb electrolyte slurry and BCZYYb electrolyte slurry were prepared by mixing the powder, binder, solvents, and plasticizer. And then, these slurries were tape-casted respectively. The anode green sheets and the electrolyte green sheets were stacked and pressed. The anode–electrolyte half-cell was obtained by firing this laminate at 1400–1500ºC for 2 h. La0.6Sr0.4CoO3–δ (LSC) paste was applied to the surface of the half-cell by screen–printing, and then, fired at 950ºC for 2 h to form a cathode.

Evaluation of the electric efficiency was conducted under the condition of 3% H2O–48.5% H2–48.5% N2 anode gas and 100% Air, which the hydrogen partial pressure in the anode gas was simulated for the methane reforming gas. Fuel flow rate was determined by Uf and the current density, for example, under Uf = 90% and i = 0.3 A cm–2 condition, H2 supply was calculated 36.9 cc min–1. Air flow rate was 264 cc min–1, which was the condition of Uair = 30% and i = 0.3 A cm–2. Electric efficiency was calculated by the following formula,

η_DC = (V/(-ΔH/nF))×Uf

Where, the n and F are the mole number and the Faraday constant, respectively. ΔH is the standard combustion enthalpy of hydrogen or methane. The value of -ΔH / nF is 1.24 V or 1.04 V in the case of hydrogen supply or methane supply respectively. In this study, 1.04 V was used for the value. V and Uf are the terminal voltage and the fuel utilization obtained by the experiment.

Figure shows the cell performance at a current density of 0.3 A cm–2 under various fuel utilization (Uf) conditions. The figure also includes a theoretical voltage line calculated by Nernst equation used the PH2 in the anode outlet gas, PO2 and PH2O in the cathode outlet gas. The maximum electric efficiency of 62% (DC) was recognized at the Uf = 85%. To compare the BZYb single-layered electrolyte PCFC, the voltage drop at high Uf condition was larger in the case of BCZYYb/BZYb double layered electrolyte. To improve the cell performance may not necessarily lead to improve electrical efficiency, as the high cell voltage could be the result of the electron leakage due to the hole conduction in BaZrO3 based materials.

Figure 1