Synergistic co-doping induced high catalytic activities of La/Fe doped Co3O4 towards oxygen reduction/evolution reactions for Zn–air batteries

Abstract

La/Fe co-doped Co₃O₄ nanoparticles supported on aminated carbon nanotubes (LaFe–Co₃O₄/NCNTs) have been demonstrated to be active bifunctional catalysts for oxygen reduction/revolution reactions (ORR/OER). With optimal La/Fe doping levels, LaFe–Co₃O₄/NCNTs exhibits an overall ORR/OER bifunctional catalytic activity higher than most catalysts reported recently. The high performance of LaFe–Co₃O₄/NCNTs mainly originates from the specific La/Fe co-doped structure of the LaFe–Co₃O₄ NPs, which increases both the ORR and OER catalytic activities of the LaFe–Co₃O₄ NPs to higher degrees. DFT calculations have shown that the La/Fe co-doping can decrease the overpotentials of both the ORR and the OER and increase the stability of the LaFe–Co₃O₄ NPs. Additionally, carbon coating can further increase the catalytic activities of LaFe–Co₃O₄/NCNTs by the decrease of the polarization losses caused by the electrical resistance. When used in zinc–air batteries (ZABs), the carbon coated LaFe–Co₃O₄/NCNTs (C@LaFe–Co₃O₄/NCNTs) can exhibit a maximum power density of 122.2 mW cm⁻², which is >20% higher than that of mixed catalysts of Pt/C + RuO₂. This, along with the much higher cycling stability of C@LaFe–Co₃O₄/NCNTs, suggests great potential for its use as a bifunctional catalyst for practical applications.