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SCIENCE CHINA Materials, Volume 60, Issue 10: 918-928(2017) https://doi.org/10.1007/s40843-017-9089-y

Acid promoted Ni/NiO monolithic electrode for overall water splitting in alkaline medium

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  • ReceivedJul 4, 2017
  • AcceptedAug 3, 2017
  • PublishedSep 5, 2017

Abstract

Exploring and designing bi-functional catalysts with earth-abundant elements that can work well for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline medium are of significance for producing clean fuel to relieve energy and environment crisis. Here, a novel Ni/NiO monolithic electrode was developed by a facile and cost-effective acid promoted activation of Ni foam. After the treatment, this obtained monolithic electrode with a layer of NiO on its surface demonstrates rough and sheet-like morphology, which not only possesses larger accessible surface area but also provides more reactive active sites. Compared with powder catalysts, this monolithic electrode can achieve intimate contact between the electrocatalyst and the current collector, which will alleviate the problem of pulverization and enable the stable function of the electrode. It can be served as an efficient bi-functional electrocatalyst with an overpotential of 160 mV for HER and 290 mV for OER to produce current densities of 10 mA cm−2 in the alkaline medium. And it maintains benign stability after 5,000 cycles, which rivals many recent reported noble-metal free catalysts in 1.0 mol L−1 KOH solution. Attributed to the easy, scalable methodology and high catalytic efficiency, this work not only offers a promising monolithic catalyst but also inspires us to exploit other inexpensive, highly efficient and self-standing noble metal-free electrocatalysts for scale-up electrochemical water-splitting technology.


Funded by

National Natural Science Foundation of China(21571073,21673090)

National Basic Research Program of China(2015CB932600)

Hubei Provincial Natural Science Foundation of China(2016CFA031)

Program for HUST Interdisciplinary Innovation Team(2015ZDTD038)

and the Fundamental Research Funds for the Central Universities.


Acknowledgment

This work was supported by the National Natural Science Foundation of China (21571073 and 21673090), the National Basic Research Program of China (2015CB932600), Hubei Provincial Natural Science Foundation of China (2016CFA031), the Program for HUST Interdisciplinary Innovation Team (2015ZDTD038) and the Fundamental Research Funds for the Central Universities. The authors also thank the Analytical and Testing Center of HUST for the measurements.


Interest statement

The authors declare that they have no conflict of interest.


Contributions statement

Li C performed the main experiments; Hou J participated in the characterization; Li C wrote the manuscript with support from Guo K, Wu Z, Wang D, Zhai T and Li H. All authors contributed to the general discussion.


Author information

Caicai Li received her BSc degree from Anyang Normal University in 2013. She is now a PhD candidate at the School of Materials Science and Engineering, Huazhong University of Science and Technology (HUST). Her research is focused on the preparation of transition metal based nanomaterials for efficient water splitting.


Huiqiao Li received her BSc degree in chemistry from Zhengzhou University in 2003, and PhD degree in physical chemistry from Fudan University in 2008. Afterward, she worked as a postdoctoral fellow for four years at the Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Japan. Currently, she is a full professor at the School of Materials Science and Engineering, Huazhong University of Science and Technology (HUST). Her research interests include energy-storage materials and electrochemical power sources, such as lithium/sodium ion batteries, supercapacitors, and electrocatalysis.


Supplement

Supplementary information

Supporting data are available in the online version of the paper.


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  • Figure 1

    Schematic illustration of the activation process to prepare the monolithic Ni/NiO electrode.

  • Figure 2

    SEM images of bare NF (a, c, e) and the obtained Ni/NiO electrode for activating the NF at 120°C for 30 min (b, d, f).

  • Figure 3

    XRD and XPS analyses of the obtained Ni/NiO electrodes with NF treated at different temperatures. (a) XRD patterns. (b) XPS spectra of Ni 2p. (c–e) The fitting of the peak areas of Ni2+ and Ni0. (f) XPS spectra of O 1s.

  • Figure 4

    (a) Linear sweep voltammetry (LSV) curves for bare NF and Ni/NiO obtained at different temperatures (60, 90, 120°C) with a scan rate of 5 mV s−1 for HER in 1.0 mol L−1 KOH. (b) Comparison of overpotential for Ni/NiO with other reported noble-metal free catalysts. (c) Tafel slopes for different Ni/NiO samples. (d) Plots of capacitive currents as a function of scan rate for Ni/NiO obtained at different temperatures. (e) Nyquist plots of the different Ni/NiO catalysts in 1.0 mol L−1 KOH. (f) LSV curves for NF-120 before and after 5,000 CV cycles, and the inset is the corresponding time-dependent current density curve under a static overpotential.

  • Figure 5

    (a) XRD pattern; (b) XPS spectra of Ni 2p and (c) XPS spectra of O 1s for the fresh, post HER and post OER Ni/NiO sample activated at 120°C for 30 min. SEM images of NF-120 after a 10 h HER (d) and OER (e) stability test.

  • Figure 6

    (a) LSV curves for bare NF and the obtained Ni/NiO at different temperatures (60,90,120°C) with a scan rate of 5 mV s−1 for OER in 1.0 mol L−1 KOH. (b) Comparison of the overpotential and Tafel slope for Ni/NiO with other reported noble-metal free catalysts. (c) Tafel slopes for different Ni/NiO samples. (d) LSV curves of NF-120 catalysts in 1.0 mol L−1 KOH before and after long-term 5,000 cycles, and the inset is the corresponding time-dependent current density curve at a static overpotential.

  • Figure 7

    (a) CV curves of Ni/NiO obtained at 120°C in 1.0 mol L−1 KOH with a scan rate of 100 mV s−1. (b) Schematic illustration of two-electrode cell using NF-120 for both anode and cathode for water splitting. (c) Current–potential response of an alkaline electrolyzer using NF-120 as catalyst for both OER and HER in 1.0 mol L−1 KOH. (d) Time dependence of catalytic current density during water electrolysis for NF-120 in 1.0 mol L−1 KOH at 1.72 V.

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