Seaweed biomass derived (Ni,Co)/CNT nanoaerogels: Efficient bifunctional electrocatalysts for oxygen evolution and reduction reactions

Developing earth-abundant, active and stable electrocatalysts which operate in two-electrode rechargeable metal-air batteries, including both oxygen evolution and reduction reactions (OER and ORR), is vital for renewable energy conversion in real application. Here, we demonstrate a three-dimensional (3D) bifunctional nanoaerogel electrocatalyst that exhibits good electrocatalytic properties for both OER and ORR. This material was fabricated using a scalable and facile method involving the pyrolysis of (Ni,Co)/CNT alginate hydrogels derived from sustainable seaweed biomass after an ion exchange process. The bifunctionality for oxygen electrocatalysis as shown by the OER-ORR potential difference (ΔE, the OER and ORR potentials are taken at the current densities of 10 mA cm^-2 and -3 mA cm^-2 in 0.1 M KOH, respectively) could be reduced to as low as 0.87 V, comparable to the state-of-the-art non-noble bifunctional catalysts. The good performance was attributed to the ternary Ni/NiO/NiCo₂O₄ catalytic center for charge transfer and 3D hierarchical mesoporous hybrid framework for efficient mass transport. More importantly, the Zn-air battery fabricated with the hybrid nanoaerogel as a bifunctional electrocatalyst displays very high energy efficiency (58.5%) and long-term stability. Prospectively, our present work may pave a new way to develop earth-abundant and low cost high-performance bifunctional electrocatalysts for rechargeable metal-air batteries.