Design and fabrication of Fe2O3/FeP heterostructure for oxygen evolution reaction electrocatalysis

https://doi.org/10.1016/j.jallcom.2021.162409Get rights and content

Highlights

  • In situ synthesis of Fe2O3/FeP heterostructures catalyst for oxygen evolution reaction (OER).

  • Tuning of electronic structure of Fe2O3/FeP heterostructures is beneficial to improve its catalytic activity.

  • Heterostructure catalyst Fe2O3/FeP exhibits enhanced OER performance with overpotential of 264 mV@10 mAcm-2.

  • Facile OER process is due to lower Tafel slope (47 mV/dec) of Fe2O3/FeP heterostructures catalyst.

Abstract

The production of an inexpensive, highly active electrocatalyst for a simple oxygen evolution reaction (OER) based on earth-abundant transition metals is still a major challenge. In addition, the ambiguity of the water splitting reaction (hydrogen evolution and OER) is a hurdle in the manufacture of suitable catalysts for the efficient water electrolysis process. Here, the synthesis of iron oxide/iron phosphide (Fe2O3/FeP) heterostructure and its counterparts Fe2O3 and FeP as cheap electrocatalysts for water electrolysis is presented. Characterization techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy were used to analyze the structure of these electrocatalysts. Heterostructure Fe2O3/FeP has been shown to be a more active electrocatalyst than its counterparts. It initiates OER at a remarkably low potential of 1.49 V vs. reverse hydrogen electrode (RHE). For this electrocatalyst, a current density of 10 mA/cm2 is achieved at an overpotential of 264 mV for OER in 1.0 M potassium hydroxide solution and the value of the Tafel slope is 47 mV dec−1, outperforming its complements (Fe2O3 and FeP) under similar conditions. The results obtained are superior to those of previously reported Fe-based OER electrocatalysts. The Fe2O3/FeP electrocatalyst has proven its long-term stability by driving OER at 1.65 V (vs. RHE) for about 12.5 h.

Introduction

The extensive use of fossil fuels is the major cause of the burgeoning environmental and energy crisis. The introduction of more sustainable methods of generating energy is urgently needed to overcome energy crises [1], [2]. The transformation of our reliance on petrochemicals towards renewable energy sources is significant [3], [4]. Hydrogen is the best source of clean renewable energy [5], [6]. Due to the fact that when it is formed and burned, only water is produced as a by-product and has a carbon dioxide-free system. The reforming process produces 90% hydrogen, which contains impurities and is not very efficient, but is still one of the largest sources of hydrogen production [7]. Hence, the development of clean energy is important in modern times due to environmental changes and the depletion of fossil fuel reservoirs. To fulfill the global demand for clean energy and to counter the decline in fossil fuel production, electrocatalytic water splitting is a promising and suitable solution [8], [9], [10]. The electrochemical splitting of water is one of the most important ways of producing hydrogen and a promising solution to meet the global energy demand [11], [12], [13]. The currently most effective and well-known electrocatalysts for water splitting are precious metals-based oxides, especially IrO2 and RuO2 [14]. However, their inadequacy and high cost limit their practical application considerably [15].

In view of the limited availability of precious metals and the higher manufacturing costs of these metals-based catalysts, it is highly desirable to design and synthesize earth-abundant and cost-effective non-noble metal-based catalysts for OER [16], [17]. Metal phosphides have recently been shown high activity as non-toxic electrocatalysts in OER. Considerable efforts have been made to synthesize metal phosphides, especially MoP, FeP, CoP and Ni2P as the best substitutes for noble metals-based catalysts for OER due to their long-term stability[18]. Niu et al. reported on hierarchical heterostructure of CoP-FeP as a bifunctional high-performance and durable electrocatalyst for OER and HER in various electrolytes [19]. Ray et al. grew the Fe-coated nickel-cobalt-phosphide nanoplates in carbon material and investigated the electrochemical splitting of water in a basic environment [20]. Fang et al. reported on the metal-organic framework-template synthesis of bimetallic selenides for OER [21]. Lei et al. manufactured an electrocatalyst by embedding FeCo in a matrix of N-doped carbon nanotubes/carbon nanosheets for the oxygen reduction reaction and OER [22]. Zhang et al. reported on a NiFe-MOF electrocatalyst for OER [23].

A rational design of a Fe2O3/FeP heterostructure based on inexpensive and earth-abundant Fe metal for OER is reported here. In the heterostructure, the interaction of Fe2O3 and FeP effectively changes the electronic structure of Fe2O3 and FeP and leads to increased intrinsic catalytic activity towards OER. An overpotential of 264 mV is required for the fabricated Fe2O3/FeP heterostructure to drive the OER with a current density of 10 mAcm-2 and a low Tafel slope value of 47 mV/dec in 1.0 M potassium hydroxide solution. The results provide useful guidelines for developing the low-cost and earth-abundant electrocatalysts for OER.

Section snippets

Materials

Iron chloride hexahydrate (FeCl3.6H2O,>98%) was purchased from Spectrum Chemicals. Potassium hydroxide (KOH, 99%) was bought from Grace Chemicals. Nafion solution (5 wt%), red phosphorus (P4, 98%) and ethanol (C2H5OH, 99.9%) were purchased from Sigma Aldrich. Sodium hydroxide (99%) was purchased from Daejung chemicals. All chemicals were used as received.

Synthesis of electrocatalysts

The hydrothermal method was used to synthesize catalysts. For iron oxide synthesis, 25 mL of 0.5 M FeCl3.6 H2O solution was kept under

Structural analysis

XRD studies were conducted to confirm the crystal structures of electrocatalysts [25]. Fig. 1 presents the XRD patterns of Fe2O3, FeP and Fe2O3/FeP electrocatalysts. The diffraction peaks in the XRD spectrum of Fe2O3 at 2θ= 24.10°, 33.02°, 35.61°, 40.81°, 49.57°, 54.13°, 57.68°, 62.51°, and 64.15° attributed to the lattice plane of (012), (104), (110), (113), (024), (116), (122), (214), and (300), respectively of rhombohedrally centered hexagonal phase [26], [27] (JCPDS No. 33–0664). X-ray

Conclusions

In summary, we have synthesized an efficient OER catalyst on the basis of a Fe2O3/FeP heterostructure, which starts oxygen evolution at an applied potential of 1.49 V (vs. RHE) and generates an OER current density of 10 mAcm-2 at only 264 mV overpotential. This improved OER performance is associated with the presence of holes in the framework of the electrocatalyst, which serve as a reservoir for an electrolyte that increases the OER performance. Moreover, the large surface area with many

CRediT authorship contribution statement

Iqbal Ahmad: Conceptualization, Experimentation, Supervision, Investigation, Resources, Methodology. Jawad Ahmed: Experimentation, Formal analysis. Saima Batool: Experimentation, Formal analysis, Writing – review & editing. Muhammad Nadeem Zafar: Formal analysis, Writing – review & editing. Amna: Formal analysis, Writing – review & editing. Zahidullah: Formal analysis, Writing – review & editing. Muhammad Faizan Nazar: Formal analysis, Writing – review & editing. Anwar Ul-Hamid: Formal

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The author (Alaa Dahshan) extends his appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through research groups program under grant number (RGP.2/89/42).

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