Nanostructured carbons containing FeNi/NiFe2O4 supported over N-doped carbon nanofibers for oxygen reduction and evolution reactions

Growth of carbon nanotubes over carbon nanofibers catalyzed by bimetallic alloy nanoparticles as a bifunctional electrode for Zn-air batteries

Design of economical, large-scale, stable, and highly active bifunctional electrocatalysts for Zn-air batteries with enhanced oxygen reduction and oxygen evolution performance is needed. Herein, a series of electrocatalysts were facilely fabricated where in situ formed bimetallic nanoparticles aided in the growth of carbon nanotubes over carbon nanofibers (MM'-CNT@CNF) during thermal treatment. Different combinations of Fe, Ni, Co and Mn metals and melamine as precursor for CNT growth were investigated. The synergistic interaction between bimetallic nanoparticles and N-doped carbon results in greatly improved bifunctional catalytic activity for both oxygen reduction and evolution reactions (ORR, OER) using FeNi-CNT@CNF as catalyst. The half-wave potential (0.80 V vs. RHE) for FeNi-CNT@CNF for ORR was close to that of Pt/C (0.79 V vs. RHE), meanwhile its stability was superior to Pt/C. Likewise, during OER, the FeNi-CNT@CNF reached a current density of 10 mA cm^-2 at a rather low overpotential of 310 mV vs. RHE compared to benchmark RuO₂ (410 mV). The rechargeable Zn-air prototype battery using FeNi-CNT@CNF as an air electrode outperformed the mixture of Pt/C and RuO₂ with discharge/charge overpotential of 0.61 V, power density of 118 mW cm^-2 at 10 mA cm^-2 and an improved cycling stability over 108 hours.

Porous Indium Tin Oxide-Supported NiFe LDH as a Highly Active Electrocatalyst in the Oxygen Evolution Reaction and Flexible Zinc-Air Batteries

The oxygen evolution reaction (OER) is crucial for hydrogen production from water splitting and rechargeable metal-air batteries. However, the four-electron mechanism results in slow reaction kinetics, which needed to be accelerated by efficient catalysts. Herein, a hybrid catalyst of novel nickel-iron layered double hydroxide (NiFe LDH) on porous indium tin oxide (ITO) is presented to lower the overpotential of the OER. The as-prepared NiFe LDH@ITO catalyst showed superior catalytic activity toward the OER with an overpotential of only 240 mV at a current density of 10 mA/cm². The catalyst also offered high stability with almost no activity decay after more than 200 h of chronopotentiometry test. Furthermore, the applications of NiFe LDH@ITO in (flexible) rechargeable zinc-air batteries exhibited a better performance than commercial RuO₂ and can remain stable in cycling tests. It is supposed that the superior catalytic behavior originates from the ITO conductive framework, which prevents the agglomeration and facilitates the electron transfer during the OER process.