Nickel foam supported Cr-doped NiCo 2 O 4 /FeOOH nanoneedle arrays as a high-performance bifunctional electrocatalyst fo
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Nickel foam supported Cr-doped NiCo2O4/FeOOH nanoneedle arrays as a high-performance bifunctional electrocatalyst for overall water splitting Tengyi Liu and Peng Diao () Key Laboratory of Aerospace Materials and Performance (Ministry of Education), School of Materials Science and Engineering, Beihang University, Beijing 100191, China © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 17 May 2020 / Revised: 17 July 2020 / Accepted: 23 July 2020
ABSTRACT Efficient and robust noble-metal-free bifunctional electrocatalysts for overall water splitting (OWS) is of great importance to realize the large-scale hydrogen production. Herein, we report the growth of undoped and Cr-doped NiCo2O4 (Cr-NiCo2O4) nanoneedles (NNs) on nickel foam (NF) as bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). We demonstrate that Cr-doping significantly improves activity for HER and OER by increasing the conductivity of NNs and allowing more active sites on NNs electrochemically accessible. When amorphous FeOOH is electrodeposited on the surface of Cr-NiCo2O4 NNs, the resulting FeOOH/Cr-NiCo2O4/NF exhibits itself as an excellent bifunctional catalyst for OWS. In the twoelectrode cell where FeOOH/Cr-NiCo2O4/NF is used both as cathode and anode for OWS, a cell voltage of only 1.65 V is required to achieve an electrolysis current density of 100 mA·cm−2. In addition, the catalyst shows a very high stability for OWS, the twoelectrode cell can operate at a consist current density of 20 mA·cm−2 for 10 h OWS with the cell voltage being stable at ca. 1.60 V. These results demonstrate that FeOOH/Cr-NiCo2O4/NF possesses an OWS performance superior to most of transition-metal based bifunctional electrocatalysts working in alkaline medium. The excellent bifunctional activity and stability of FeOOH/Cr-NiCo2O4/NF are attributed to the following reasons: (i) The NN structure provides a large specific surface area; (ii) the high conductivity of Cr-NiCo2O4 enables more active centers on the far-end part of NNs to be electrochemically reached; (iii) the deposition of FeOOH supplies additional active sites for OWS.
KEYWORDS Cr-doped nickel cobaltite, bifunctional electrocatalyst, iron oxyhydroxide, hydrogen evolution reaction, oxygen evolution reaction, overall water splitting
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Introduction
The increase of both energy consumptions and global environmental issues is stimulating scientists to search for a clean, eco-friendly and renewable energy resource to replace fossil fuels [1–3]. Hydrogen (H2) has been frequently advocated as a promising energy carrier for its high energy density and zero environmental impact upon combustion [4, 5]. Water electrolysis, which consists of two half reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) [5–7], is widely recognized as an ideal and sustainable way to produce H2, especially if the electricity can be converted from renewable energy sources such as solar, wind and wave
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