Elsevier

Nano Energy

Volume 20, February 2016, Pages 29-36
Nano Energy

Rapid communication
One-step synthesis of self-supported porous NiSe2/Ni hybrid foam: An efficient 3D electrode for hydrogen evolution reaction

https://doi.org/10.1016/j.nanoen.2015.12.008Get rights and content

Highlights

  • Three-dimensional (3D) porous NiSe2/Ni hybrid foams are synthesized via one-step selenization.

  • This growth procedure can be compatible with sizable electrodes.

  • The hybrid foam can be directly used as self-supported and efficient 3D electrodes for the HER.

  • The HER performance is excellent featured by low Tafel slope and large current density.

Abstract

The search of cheap, earth-abundant and efficient hydrogen evolution reaction (HER) catalysts is significant for sustainable hydrogen economy. Here we introduce a simple and cost-effective strategy for one-step synthesis of 3D porous NiSe2/Ni hybrid catalysts from commercially available Ni foams via thermal selenization. This catalyst exhibits superior catalytic performance featured by a small overpotential (~143 mV) to afford 10 mA/cm2, small Tafel slope (49.0 mV/dec), large exchange current density (15.7 μA/cm2) and good stability in acid, which benefits from the good electrical conductivity of NiSe2 catalysts on Ni foam and the increase of additional porous structures at NiSe2 surface. This performance is superior to most of well-studied MoS2 or WS2-based catalysts, and the exchange current density is much larger than CoSe2 or MoS2-based catalysts. This achievement provides a straightforward and effective route to produce cheap and efficient catalysts from commercially available materials for large-scale water splitting.

Introduction

Hydrogen (H2), directly generated from the splitting of abundant water, is a promising energy carrier to replace natural fossil fuels and relieve the growing greenhouse effects [1]. Hydrogen evolution reaction (HER), which is a half reaction of water splitting, is an appealing and efficient route for H2 generation without any pollution or greenhouse gas emission [2], [3]. The prerequisite for the HER is to find an efficient and robust catalyst to minimize the activation energy of H2 formation on the catalyst surface, and achieve large cathodic current densities at low overpotentials [4], [5]. Pt-group metals are the best HER catalysts, but they are expensive and rare, which greatly restricts the industrial production of H2 [6]. Thus, it remains an interesting and ongoing topic to seek efficient alternatives to replace Pt with low cost [7], [8], [9].

Earth-abundant Ni-based alloys are good substitutes for replacing Pt-based HER electrocatalysts, but they can only be applied in alkaline environment because of the corrosion issue in acid [10]. Instead, first-row transitional metal dichalcogenides, which are common minerals in earth with the general formula MX2 (M=Fe, Co, or Ni and X=S or Se), are expected to serve as promising substitutes for noble Pt metals as the HER electrocatalysts for which they are extremely cheap and stable in both acidic and alkaline environments [11], [12]. Particularly, different from semiconducting pyrites such as FeS2 or NiS2, nickel diselenide (NiSe2) is intrinsically a conductive metal, which makes it advantageous as an electrocatalyst [13]. Despite the exploration of using it as HER catalysts over 20 years [14], there have been only a few scattered studies focusing on this material to date, and the HER performance is far from satisfactory probably due to the poor electrical conductivity of its nanostructures or electrical contact with the support [15], [16]. Interestingly, recent studies demonstrate that the catalytic performance of its representative CoS2 or CoSe2 could be improved by structural engineering [11], or by synergistic coupling with other functional nanostructures like carbon-based materials [15], [16]. However, the growth procedures for the catalysts are somewhat complicated with multiple steps involved. As such, it is highly desirable to develop a simple and straightforward approach to fabricate cost-effective NiSe2-based catalysts with high HER activity and electrochemical stability. Even better, it is promising to synthesize the catalyst in large scale with the starting material commercially available. In this regard, Ni foam is a good and cheap starting material, since it is commercially employed as the support for material synthesis [17] or electrochemical tests [18]. In this work, by partial selenization of Ni foam in Ar atmosphere, we firstly report a new strategy for one-step synthesis of three-dimensional (3D) porous NiSe2/Ni hybrid architectures, which are demonstrated to be efficient and robust HER electrocatalysts with self support without any polymer binders, featured by relatively low onset overpotential (~88 mV), high cathode current density (10 mA/cm2 at -143 mV, 100 mA/cm2 at -196 mV) and small Tafel slope (~49.0 mV/dec). All the potentials shown here are referred to the reversible hydrogen electrode (RHE). Benefiting from the porous structure, low cost and high electrical conductivity, Ni foam is of great potential as the support and current collector for NiSe2 catalysts. Meanwhile, this heterogeneous structure shows good stability in acid electrolyte, which is essential for any promising HER electrocatalyst. The high HER performance is likely attributed to the improved electrical contact between NiSe2 catalysts and the electrode, and the increase of additional porous structures during NiSe2 growth, making this architecture efficient and stable in acid. Considering that the synthesis procedure, just by the selenization of commercially available Ni foam, is straightforward and inexpensive, this method can be compatible with sizable electrodes, confined only by the dimension of the growth chamber and the size of Ni foam.

Section snippets

Preparation of 3D porous NiSe2/Ni foam

The synthesis of the NiSe2/Ni catalysts was carried out in a quartz tube furnace having a diameter of 3/4 in.. The starting Ni foam was cut into small pieces around 1.0 cm2 in area, and placed at the centre of the tube furnace. Selenium powder (99.5%, Alfa Aesar) was used as the Se source, which was placed at the upstream of the furnace. Before heating the furnace, a 600 sccm Ar gas was introduced into the chamber to purge the system for 1 h. Then the furnace was programmed to the desired

Results and discussion

In our experiments, a piece of Ni foam (~1 cm2) was directly put in a tube furnace with Se powder as the Se source and the growth temperature was in the range from 450 °C to 600 °C (Experimental Section). The selenization was performed for 1 h in pure Ar atmosphere (99.999%, ultrahigh purity). Then scanning electron microscopy (SEM) was used to image the microscopic structures of the as-grown samples synthesized at different temperatures (Fig. 1). According to the SEM images of the starting Ni

Conclusions

Through thermal selenization of commercially available Ni foams, we have developed a simple strategy to grow NiSe2 electrocatalysts on the conductive Ni foam to form 3D porous NiSe2/Ni electrodes. Considering the low cost of the starting Ni foam, this approach is cheap and time-saving for material synthesis and electrode fabrication. Even though the process is simple, the HER performance of the as-grown NiSe2/Ni catalysts is pretty good, featured by small Tafel slopes of ~49 mV/dec, large

Acknowledgments

The authors would like to thank the support from US Defense Threatening Reduction Agency (DTRA) under grant FA 7000-13-1-0001. S. C. would also like to acknowledge TcSUH Robert A.Welch Professorships in High Temperature Superconducting (HTSg) and Chemical Materials (E-0001).

Dr. Haiqing Zhou is currently a postdoctoral fellow in Department of Physics and TcSUH at University of Houston, USA. He received his Ph.D. degree in Prof. Lianfeng Sun׳s group in National Center for Nanoscience and Technology, Chinese Academy of Sciences in China in 2012, and a BS degree from Hunan Normal University, China in 2007. He joined Prof. Ren׳s group since 2014. His research mainly focuses on the synthesis of two-dimensional single crystals of transition-metal dichalcogenides,

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    Dr. Haiqing Zhou is currently a postdoctoral fellow in Department of Physics and TcSUH at University of Houston, USA. He received his Ph.D. degree in Prof. Lianfeng Sun׳s group in National Center for Nanoscience and Technology, Chinese Academy of Sciences in China in 2012, and a BS degree from Hunan Normal University, China in 2007. He joined Prof. Ren׳s group since 2014. His research mainly focuses on the synthesis of two-dimensional single crystals of transition-metal dichalcogenides, graphene and embedding them into three-dimensional porous architectures for water splitting.

    Dr. Yumei Wang is currently an Associate Professor in the Institute of Physics, Chinese Academy of Sciences. She received her Ph.D. degree from the Institute of Physics. Her research interest is mainly on high-resolution electron microscopy, structure and microstructure of functional materials, and application of electron crystallography image processing.

    Ran He is currently a Ph.D. candidate of Physics at the University of Houston. He got his Bachelor degree from Northeastern University, P. R. China. His study mainly focuses on the transportation of electron and phonon in mid-to-high temperature thermoelectrics materials. He is a recipient of C. W. Chu scholarship from Texas center of Superconductivity at the University of Houston.

    Dr. Fang Yu is currently a postdoctoral fellow in Department of Physics and TcSUH at University of Houston, USA. She received his Ph.D. degree from National Center for Nanoscience and Technology, Chinese Academy of Sciences in China in 2012, a BS degree from Hunan Normal University, China in 2007. She joined Prof. Zhifeng Ren׳s group since 2013. Her research mainly focuses on the synthesis of vertically aligned carbon nanotube forests or individual single-walled carbon nanotubes and the unzipping of individual single-walled carbon nanotubes into graphene nanoribbons catalyzed by metal nanoparticles.

    Jingying Sun is currently a second year graduate student in Department of Physics and TcSUH at the University of Houston. She received her B.S. degree in Physics from Jilin University, China. Her current research is mainly on lithium-ion battery and in-situ transmission electron microscopy.

    Dr. Feng Wang is currently a postdoctoral fellow in Department of Physics and TcSUH at University of Houston, USA. He received his B.S. from Nanjing University of Technology in China in 2005 and Ph.D. degree in University of Cincinnati, USA, both in Materials Science. He joined Prof. Zhifeng Ren׳s group in 2013. His research interest includes particle surface modification, porous film fabrication and it׳s application in catalysis.

    Dr. Yucheng Lan is currently an assistant professor in Department of Physics and Engineering Physics at the Morgan State University. He obtained his Ph.D. degree in condensed matter physics from the Institute of Physics, Chinese Academy of Sciences, and master and bachelor degrees in solid state physics from Jilin University. He specializes in X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy and Raman scattering. He has published extensively in the areas of superconductors, III–V nitrides, thermoelectric materials, nanomaterials and nanosensors.

    Dr. Zhifeng Ren is currently an M.D. Anderson Chair Professor in Department of Physics and TcSUH at the University of Houston. He obtained his Ph.D. degree from the Institute of Physics Chinese Academy of Sciences, master degree from Huazhong University of Science and Technology, and bachelor degree from Xihua University. He was a postdoc and research faculty at SUNY Buffalo before joining BC as an Associate Professor in 1999. He specializes in thermoelectric materials, solar thermoelectric devices, photovoltaic materials and systems, carbon nanotubes and semiconducting nanostructures, nanocomposites, bio agent delivery and biosensors, flexible transparent conductors, superconductors, etc.

    Dr. Shuo Chen is currently an assistant professor in Department of Physics at the University of Houston. She earned her BS degree in Physics at Peking University, China and a Ph.D. degree from the Department of Physics at Boston College. Her research interests cover the material/device fabrication for clean/green energy application purposes and in situ Transmission Electron Microscopy.

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