Highly Durable Bifunctional Gas Diffusion Electrodes Fabricated with Melilite-Type Fe/Co/Ni-Mixed Oxide Electrocatalysts

Here, we report the fabrication and characterization of gas diffusion electrodes (GDEs) incorporating melilite-type oxide electrocatalysts. Fe/Co/Ni-mixed melilites AE2Fe2-2y(Co1-xNix)yGe1+yO7 (AE = Sr and Ba) were successfully synthesized in a limited cationic ratio with Ni amounts equal to or smaller than 0.5 in the transition-metal site (i.e., x x y <= 0.5). The resultant Fe/Co/Ni-mixed melilites showed high OER activity in alkaline media, and the OER performance with the optimal composition Ba2Fe0.4Co0.6Ni0.2Ge1.8O7 (BFCNG) was superior to those of Ni-free Fe/Co-melilites and a noble metal catalyst RuO2. A gas diffusion electrode (GDE) with BFCNG-loading effectively worked in charge-discharge cyclic tests, with a total overpotential of ORR/OER polarizations, Delta E equivalent to eta ORR + eta OER = 0.756 V at +/- 40 mA cm-2. Furthermore, the BFCNG-loaded GDE showed a record-high accumulated capacity of 20,000 mAh cm-2 during 1000 h of operating time. The high durability is likely attributed to the bifunctionality of BFCNG with suppressed ORR/OER overpotentials. Because of their thermal stability, the melilite catalysts can be embedded in GDEs without deterioration and effectively activated during the subsequent electrochemical reactions. Such on-site activation type materials are suitable as practical electrocatalysts used in metal-air batteries.

Automated summary

This study reports the fabrication and characterization of gas diffusion electrodes (GDEs) incorporating melilite-type oxide electrocatalysts. The mixed melilites showed high OER activity and durability, with potential applications in practical electrocatalysis for metal-air batteries.