Cu2-xSe@CuO core-shell assembly grew on copper foam for efficient oxygen evolution

https://doi.org/10.1016/j.ijhydene.2019.10.088Get rights and content

Highlights

  • Cu2-xSe@CuO core-shell structure forms by the in situ electrochemicall oxidation of Cu2Se.

  • A formation model for the core-shell structure catalyst is proposed.

  • The phase change of copper selenide is clearly explained in OER process.

  • The presence of semi-metallic Cu2-xSe promotes the OER performance of CuO.

Abstract

Hydrogen production from electrolyzed water is a mature technology and has great development prospects in terms of energy conversion and utilization. However, the kinetically sluggish oxygen-evolution reaction becomes the limiting step in the electrolysis of water. Copper-based materials have been reported as a good choice to catalyze the oxygen evolution reaction, but their performance is poor. We describe a Cu2-xSe@CuO/copper foam core–shell structure from the in situ electrochemical oxidation of Cu2Se/copper foam to promote the oxygen-evolution reaction performance. The presence of a semi-metallic Cu2-xSe core and nanostructured CuO shell at a current density of 10 mA cm−2 requires a low overpotential of 253 mV. The Tafel slope was only 73 mV dec−1. The preparation of Cu2-xSe@CuO on three-dimensional copper foam facilitates the reaction.

Introduction

Water electrolysis powered by renewable clean-energy sources (for instance: solar energy, wind, or wave power) is an efficient pathway for the approaching hydrogen economy. The electrolysis of water includes the oxygen-evolution reaction (OER) and hydrogen-evolution reaction (HER) processes. The OER is accompanied by multi-step proton-coupled electron transfer [[1], [2], [3]], which shows sluggish kinetics, and thus this step has become the limiting step in the electrolysis of water [4,5]. Common commercial OER catalysts include ruthenium (Ru) and iridium (Ir) oxides [6,7]. However, their scarcity and cost hinder their industrialization. Thus, inexpensive and efficient catalysts must be used to accelerate the OER reaction rate and afford a high current at a low overpotential [[8], [9], [10], [11]].

Over recent decades, many non-noble metal oxides and hydro(oxy)oxides have been developed and they exhibit excellent performance in OER [[12], [13], [14], [15]]. Because of their unique electron configuration, first-row transition metal dichalcogenides (TMCs, T = Cu, Fe, Co, Ni, C = S, Se, Te) have been studied in areas, such as energy conversion and storage and metal-air fuel cells in recent years [[16], [17], [18], [19], [20], [21]]. Metal selenides (such as (NiCo)0.85Se/CFC [22], NiSe/NF [16], and α-CoSe/Ti [23]) have been reported to exhibit good anodic OER performance. Nevertheless, their active forms need to be explored. Chang's group found that metallic cobalt-phosphide core coated with an oxide-layer (CoOx) structure that was formed during passivation favored the OER [24]. A poorly crystalline or amorphous transition-metal oxide would exhibit good electrochemical properties because it possesses more defective and active sites for OER [25,26]. Chen et al. proposed an in situ electrochemical oxidation tuning method to transform metal sulfides into the corresponding amorphous metal oxides for the anode OER [27].

The contribution of copper-based materials to the development of OER electrocatalysts cannot be ignored [[28], [29], [30], [31]]. A catalytic performance promotion is required for copper-based electrocatalysts, compared with Ni and Co metal catalysts [32]. Recently, Hao et al. developed Cu3P/NF microsheets with an overpotential of 290 mV and a current density of 10 mA cm−2 for the OER [33]. Du's group reported that the CuO/Cu foil nanowire at a current density of 10 mA cm−2 required a small overpotential of 580 mV [34]. We describe here the Cu2-xSe@CuO/copper foam (CF) core–shell structure that yields a current density of 10 mA cm−2 with a low overpotential of only 253 mV.

Section snippets

Reagents and materials

Selenium dioxide and KOH were from Aladdin Ltd. (Shanghai, China). Ethanol and HCl were from Innochem Technology Co., Ltd. (Beijing China) Copper foam was from Metal Materials Co., Ltd. (Shanxi China) deionized water was used.

Preparation of Cu2Se/CF

Copper foam (CF) was rinsed with 2 M HCl for ~10 min and then ethanol and deionized water each for 10 min, before being rinsed with ethanol and deionized water three times each. The CF substrate was prepared during the preparation of the experiment. SeO2 powder was

Results and discussion

Cu2Se/CF was obtained by direct selenizing of CF in SeO2 solution with ultrasound (see Supporting Information (SI) for details). SeO2 was dissolved in water to form H2SeO3. CF reacted with H2SeO3to form Cu+ and Se2−. Subsequently, Cu+ was deposited with Se2− to form Cu2Se on the surface of CF. The presence of ultrasound can accelerate the chemical reaction in the liquid–solid heterogeneous systems.SeO2 + H2O → H2SeO3Cu + H2SeO3 → Cu+ + Se2-2Cu+ + Se2− → Cu2Se

Low and high-magnification SEM

Conclusions

We have prepared Cu2-xSe@CuO/CF by the in situ activation of Cu2Se in alkaline solution. The presence of a semi-metallic Cu2-xSe core and a nanostructure CuO shell promoted the catalytic performance for OER. An overpotential of only 253 mV is required to drive a current density of 10 mA cm−2. The corresponding Tafel slope is low at 73 mV dec−1. The material provides excellent resistance to corrosion during long-term application at a current density of 20 mA cm−2.

Acknowledgment

The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (No. 21878202, 21975175), the Research Project Supported by Shanxi Scholarship Council of China (No. 2017-041), the Natural Science Foundation of Shanxi Province (No. 201801D121052), and the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi.

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