Enhanced performance of Ni0.8Co0.15Al0.05LiO2-δ-Ba0.875Fe0.875Zr0.125O3 composite symmetric electrode via proton-coupled electron transfer for low-temperature SOFCs

Since the emergence of low-temperature solid oxide fuel cells (LTSOFCs) based on protonic semiconductor oxide electrolytes, H + /O 2− /e − triple-conducting layered Ni 0.8 Co 0.15 Al 0.05 LiO 2-δ (NCAL) has become a very successful electrode material due to its dual catalytic activities to hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). However, the performance of semiconductor-based LTSOFCs is primarily limited by electrode polarization. Thus, enhancing the separation of electrons and protons at the electrode/electrolyte interface is vital. In this work, the NCAL symmetric electrode was modified with a triple-conducting perovskite Ba 0.875 Fe 0.875 Zr 0.125 O 3-δ (BFZ) to form a 3D heterostructure composite electrode for semiconductor-based SOFCs. The influence of composite composition on the electrochemical performance of NCAL-BFZ composite electrodes has been investigated, and the optimal performance was achieved by the composite electrode with 10 wt% BFZ (NCAL-BFZ10). The polarization resistance of the fuel cell based on a semiconductor CeO 2 electrolyte was recorded as 0.22 Ω cm 2 and 0.16 Ω cm 2 at 550°C for the NCAL symmetric electrode and the NCAL-BFZ10 composite symmetric electrode, respectively. Accordingly, the peak power density of the fuel cell employing the NCAL symmetric electrode reached 633 mW cm −2 , while the device with the NCAL-BFZ10 composite symmetric electrode exhibited superior performance, 873 mW cm −2 at 550°C. The success of modification strategy on NCAL electrode is attributed to enhanced charge separation. A proton-coupled electron transfer (PCET) mechanism is proposed to describe the separation of electron and proton in the whole cell, verified by Fourier Transform Infrared (FTIR), Distribution of Relaxation Time (DRT), isotopic fuel cells, proton-filtering fuel cell, and comparative polarization resistance and conductivity results in different atmospheres were performed. These results establish the NCAL-BFZ heterostructure composite as a promising symmetric electrode for low-temperature SOFCs.