| Summary: | There is tremendous potential for both small- and large-scale applications of low-temperature operational ceramic fuel cells (LT-CFCs), which operate between 350 °C and 550 °C. Unfortunately, the low operating temperature of CFCs was hampered by inadequate oxygen reduction electrocatalysts. In this work, the electrochemical characteristics of a semiconductor heterostructure composite based on WO<sub>3</sub>-CaFe<sub>2</sub>O<sub>4</sub> deposited over porous Ni-foam are investigated. At low working temperatures of 450–500 °C, the developed WO<sub>3</sub>-CaFe<sub>2</sub>O<sub>4</sub> pasted on porous Ni–foam heterostructure composite cathode exhibits very low area-specific resistance (0.78 Ω cm<sup>2</sup>) and high oxygen reduction reaction (ORR) activity. For button-sized SOFCs with H<sub>2</sub> and atmospheric air fuels, we have demonstrated high-power densities of 508 mW cm<sup>−2</sup> running at 550 °C, and even potential operation at 450 °C, using WO<sub>3</sub>-CaFe<sub>2</sub>O<sub>4</sub> seeded on porous Ni-foam cathode. Moreover, WO<sub>3</sub>-CaFe<sub>2</sub>O<sub>4</sub> composite heterostructure with Ni foam paste exhibits very low activation energy compared to both WO<sub>3</sub> and CaFe<sub>2</sub>O<sub>4</sub> alone, which supports ORR activity. To comprehend the enhanced ORR electrocatalytic activity of WO<sub>3</sub>-CaFe<sub>2</sub>O<sub>4</sub> pasted on porous Ni-foam heterostructure composite, several spectroscopic tests including X-ray diffraction (XRD), photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS) were used. The findings may also aid in the creation of useful cobalt-free electrocatalysts for LT-SOFCs.
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