Apically Dominant Mechanism for Improving Catalytic Activities of N-Doped Carbon Nanotube Arrays in Rechargeable Zinc-Air Battery
2018-01-08T16:33:39Z (GMT)
by
<p>The
oxygen reduction (ORR) and oxygen evolution reactions (OER) in Zn-air batteries
(ZABs) require highly efficient, cost-effective and stable electrocatalysts as
replacements to traditionally high cost, inconsistently stable and low poison
resistant Platinum group metals (PGM) catalysts. Although, nitrogen-doped
carbon nanotube (NCNT) arrays have been developed over recent decades through various
advanced technologies are now capable of catalyzing ORR efficiently, their
underdeveloped bifunctional property, hydrophobic surface, and detrimental
preparation strategy are found to limit practical large-scale commercialization
for effective rechargeable ZABs. Here, we have demonstrated fabrication of a
three-dimensional (3D) nickel foam supported NCNT arrays with CoNi
nanoparticles (NPs) encapsulated within the apical domain (denoted as <a></a><a>CoNi@NCNT/NF</a>)
that exhibits excellent bifunctional catalytic performance toward both ORR
(onset potential of 0.97 V vs. RHE) and OER (overpotential of 1.54 V vs. RHE at
10 mA cm<sup>-2</sup>). We further examined the practicability of this
CoNi@NCNT/NF material being used as an air electrode for rechargeable ZAB coin
cell and pouch cell systems. The ZAB coin cell showed <a>a
peak power density of 108 mW cm<sup>-2</sup> with an energy density of 845 Wh
kg<sub>Zn</sub><sup>-1</sup> and robust rechargeability over 28h</a> under
ambient conditions, which exceeds the performance of PGM catalysts and leading
non-PGM electrocatalysts. In addition, density functional theory (DFT)
calculations revealed that the ORR and OER catalytic performance of the
CoNi@NCNT/NF electrode are mainly derived from the d-orbitals from the CoNi NPs
encapsulated within the apical dominant end of the NCNTs.</p>