Metal-organic frameworks/ hydrotalcite/graphene oxide sandwich composites derived Fe-Ce@GSL hierarchical materials as highly efficient catalysts for rechargeable Zn-air batteries.

The fabrication of efficient bi-functional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) applied in energy storage and conversion devices like Zn-air batteries to solve the growing energy and environmental crises has attracted great attentions. In this work, the Fe-Ce@GSL catalysts have developed by first constructing the MOF/LDH/GO templates with multi-stage mixed growth method followed by calcining the template at high temperature. Fe-Ni-LDH (hydrotalcite) plays the role of linking the metal organic frameworks (Fe-Ce-MOF) and graphene oxides (GO), avoiding the separation of MOFs derivatives and GO sheets during pyrolysis process. Rare-earth metal oxide (CeO) featuring with abundant oxygen vacancies dispersed on the surface of transition-metal oxide can efficiently improve the stability of catalysts. The optimal Fe-Ce@GSL-800 catalysts exhibit excellent ORR/OER performances with the potential gap between ORR (E = 0.87 V) and OER (E = 1.59 V) of 0.720 V. The aqueous Zn-air battery assembled with Fe-Ce@GSL-800 catalysts exhibits outstanding performances with high open circuit voltage (1.56 V), large specific capacity (801.1 mAh/g@10 mA.cm), and good charge-discharge cycle performances (>500 h). The Fe-Ce@GSL-800 based solid-state Zn-air battery also delivers an excellent performance with high specific capacity (791.7 mAh/g@5 mA.cm) and long cycle stability (>230 h).