A robust bifunctional catalyst for rechargeable Zn-air batteries: Ultrathin NiFe-LDH nanowalls vertically anchored on so

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A robust bifunctional catalyst for rechargeable Zn-air batteries: Ultrathin NiFe-LDH nanowalls vertically anchored on soybeanderived Fe-N-C matrix Meng Zhang1, Jiting Zhang1, Siyi Ran1, Lingxi Qiu1, Wei Sun2 (), Ying Yu1 (), Jisheng Chen1, and Zhihong Zhu1 () 1

Institute of Nano-science and Nano-technology, College of Physical Science and Technology, Central China Normal University, Wuhan 430079, China 2 Key Laboratory of Laser Technology and Optoelectronic Functional Materials of Hainan Province, College of Chemistry and Chemical Engineering, Hainan Normal University, Haikou 571158, China © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 4 August 2020 / Revised: 8 October 2020 / Accepted: 9 October 2020

ABSTRACT NiFe layered double hydroxide (NiFe-LDH) nanosheets and metal–nitrogen–carbon materials (M–N–C, M = Ni, Fe, Co, etc.) are supreme catalysts in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) process, respectively. Nevertheless, the monotonic performance and insufficient stability severely hamper their practical application in rechargeable batteries. Herein, we simultaneously combine ultrathin NiFe-LDH nanowalls with renewable soybean-derived Fe-N-C matrix to obtain a hybrid materials (NiFe-LDH/FeSoy-CNSs-A), which exhibits robust catalytic activities for OER (Ej=10 = 1.53 V vs. RHE) and ORR (E1/2 = 0.91 V vs. RHE), with a top-notch battery parameters and stability in assembled rechargeable Zn-air batteries. Intensive investigations indicate that the vertically dispersed NiFe-LDH nanosheets, Fe-N-C matrix derived from soybean and the strong synergy between them are responsible for the unprecedented OER and ORR performances. The key role of intrinsic N defects involved in the hybrid materials is firstly specified by ultrasoundassisted extraction of soy protein from soybean. The exquisite design can facilitate the utilization of sustainable biomass-derived catalysts, and the mechanism investigations of N defects and oxygenic groups on the structure–activity relationship can stimulate the progress of other functional hybrid electrocatalysts.

KEYWORDS biomass, Fe-N-C, NiFe-LDH, oxygen reduction reaction, oxygen evolution reaction, rechargeable Zn-air batteries

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Introduction

Reversible Zn-air battery is a hopeful alternative to resolve the current global energy crisis and serious environmental issues for their stable performance, non-pollution, and high theoretical energy density (1,084 Wh·kg−1) [1]. However, the inherent depressed oxygen evolution reaction (OER) kinetics during recharge and insufficient oxygen reduction reaction (ORR) activity during discharge greatly hinder their commercialization. Therefore, it remains the huge challenges to explore highefficiency bifunctional catalysts. By decades of efforts, NiFe layered double hydroxide (NiFeLDH) nanosheets, as low-budget non-precious metal catalysts (NPMCs) are widely known for their remarkable OER catalytic activity [2–7]. However, the inherent low conductivity and self-