Elsevier

Applied Surface Science

Volume 567, 30 November 2021, 150835
Applied Surface Science

Full Length Article
Formation of hierarchical NiFe Prussian blue analogues/Prussian blue on nickel foam for superior water oxidation

https://doi.org/10.1016/j.apsusc.2021.150835Get rights and content

Highlights

  • A method for the synthesis of NiFe-PBA/PB nanocubes on nickel foam was developed.

  • Ammonium persulfate acts as an oxidant and promoter.

  • Sodium citrate acts as a reducing agent and morphological regulator.

  • The activated Ni0.59Fe-PB-3-110 catalyst exhibits optimal catalytic activity.

  • Low overpotential of 230 mV at 50 mA cm−2 was obtained.

Abstract

A series of NiFe Prussian blue analogues (PBAs)/Prussian blue (PB) nanocubes (NizFe-PB-x-y) on nickel foam were synthesized using a one-pot redox reaction and deposition strategy. The growth and particle size of NizFe-PB-x-y can be adjusted by changing the ammonium persulfate concentration (x) and hydrothermal temperature (y). To explore the role of individual reactants, three other catalysts were synthesized by changing the reaction conditions, including sea urchin-like FeOOH, Fe4[Fe(CN)6]3 cube, and NiFe PBA/FeOOH grain. During the reaction, ammonium persulfate may acted as a promoter and oxidant, sodium citrate as a reducing agent and morphological regulator, potassium ferricyanide as a single iron source, and nickel foam as a nickel source and substrate. More importantly, compared with other catalysts, the electrochemically activated Ni0.59Fe-PB-3-110 catalyst manifests the most outstanding catalytic activity in 1.0 M KOH electrolyte solution, with current densities of 50 and 800 mA cm−2, requiring only 230 and 305 mV overpotential, respectively. It is anticipated that the novel strategy will not only contribute to the design and development of hierarchical three-dimensional PB or PBAs supported by conductive substrates, but also further promote their applications in the field of electrocatalysis and energy storage.

Graphical abstract

A novel method was designed to synthetize the NiFe Prussian blue analogues (PBAs)/Prussian blue (PB) nanocubes (NizFe-PB-x-y) on nickel foam from a single iron source for superior water oxidation.

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Introduction

Electrocatalytic water splitting, easy to operate and environment friendly, is a sustainable and effective approach for the large-scale hydrogen production [1], [2]. However, oxygen evolution reaction (OER) poses considerable challenges to large-scale water splitting due to slow kinetic processes [3], [4], [5]. So far, noble metal catalysts, represented by IrO2 and RuO2, have been still recognized as the benchmark catalysts for OER [6], [7]. Unfortunately, their extensive commercial applications are limited because of scarcity and high price [8], [9]. Thus, the research of non-noble metal electrocatalysts with adjustable structures and compositions has been the focus of source research [10], [11], [12], [13].

Prussian blue (PB) and prussian blue analogues (PBAs) have wide range of applications in catalysis, energy conversion and storage because of the unique frame structure and three-dimensional pores and the tunability of metal ions [14]. Its general formula is AxM[M′(CN)6]y·nH2O, where M′ and M represent transition metal ions and A represents the monovalent cation [15], [16]. Generally, most of the prepared PBAs materials and their derivatives are powder, and the active materials are coated on the conductive fluid by using adhesive, which can easily lead to the overall reduction of the active area of the material and the mechanical stability of the conductivity [17], [18], [19], [20], [21]. In addition, the powder material is easy to aggregate and collapse during heat treatment, which leads to the decline of performance. Based on these considerations, it remains a serious challenge to prepare hierarchical three-dimensional (3D) PBAs or their derivatives with promising applications. Significantly, the in situ synthesis of PBAs or PBA derivatives on 3D conductive substrates (e.g. nickel foam and copper foam) can not only reduce the contact resistance and improve the mechanical stability and active area of the catalyst, but also the conductive substrate itself has a certain catalytic activity, which can better promote electron transfer and thus improve the catalytic activity [22], [23], [24], [25].

Up to now, the preparation of PB or PBAs on conductive substrates is generally through ion exchange, in situ redox reaction and electrochemical deposition [23], [26], [27]. For example, Wang and co-workers first synthesized two-dimensional flake Co(OH)2 on the nickel foam substrate and then used it as a template to obtain hierarchical Co(OH)2@PBA/NF by ion exchange reaction [26]. Wang and co-workers reported that a variety of PBA can be synthesized on different metal substrates by interfacial redox reactions and deposition processes [23]. Tian and co-workers used one-step electrochemical deposition strategy to synthesize prussian blue layers on carbon paper films [27]. However, there may be some drawbacks such as poor performance, time consuming or crystallinity for the above methods.

In this study, we employ a one-pot special redox reaction and deposition strategy to synthesize a series of NiFe-PBA/PB nanocubes (NizFe-PB-x-y) on nickel foam by varying the hydrothermal temperature and the concentration of the ammonium persulfate. Both the amount of growth and size of NiFe-PBA/PB can be adjusted by hydrothermal temperature and ammonium persulfate content. To explore the role of individual reactants, three other catalysts were synthesized by changing the reaction conditions, including sea urchin-like FeOOH, Fe4[Fe(CN)6]3 cube, NiFe PBA/FeOOH grain. During the reaction, ammonium persulfate may acted as a promoter and oxidant, sodium citrate may as a reducing agent and morphological regulator, potassium ferricyanide as a single iron source, and nickel foam as a nickel source and substrate. Compared with other catalysts, the electrochemically activated Ni0.59Fe-PB-3-110 catalyst manifests the most outstanding catalytic activity in 1.0 M KOH electrolyte solution with current density of 50 and 800 mA cm−2, requiring only 230 and 305 mV overpotential, respectively.

Section snippets

Chemicals and reagents

Potassium ferricyanide (K3[Fe(CN)6]) was obtained from Shanghai Macklin Biochemical Co., Ltd., (Shanghai, China). Sodium citrate tribasic dihydrate (Na3C6H5O7·2H2O) was obtained from Tianjin Reagent Co., Ltd., (Tianjin, China). Ammonium peroxydisulfate ((NH4)2S2O8) was obtained from Shanghai Titan Technology Co., Ltd., (Shanghai, China). Nafion D-521 solution (5% w/v, Alfa Aesar) was bought from Sigma-Aldrich Chemical Reagent Co., Ltd., (Shanghai, China). Nickel foam (NF) (1 cm × 3 cm) was

Synthetic route and mechanism

It can be seen from the synthesis process of the catalysts that the raw material has a decisive effect on the composition and morphology for the catalysts (Fig. 1). If only ammonium persulfate and potassium ferricyanide are used as reactants, the product is sea urchin-like FeOOH, which may be explained by the following equation:[Fe(CN)6]3- + 3NH4++ 8H2O + 3O2 → FeOOH + 6CO2 + 9NH3

At this point, the role of ammonium persulfate is to promote the production of FeOOH. Then if sodium citrate is

Conclusion

Overall, we employ a one-pot special redox reaction and deposition strategy to synthesize a series of NiFe-PBA/PB nanocubes (NizFe-PB-x-y) on nickel foam by varying the hydrothermal temperature and the concentration of the ammonium persulfate. Both the amount of growth and size of NiFe-PBA/PB can be adjusted by hydrothermal temperature and ammonium persulfate content. Compared with other catalysts, the electrochemically activated Ni0.59Fe-PB-3-110 catalyst manifests the most outstanding

CRediT authorship contribution statement

Li Li Wu: Conceptualization, Methodology, Investigation, Formal analysis, Software, Writing – original draft. Xiao Hui Chen: Investigation, Software, Validation. Qing Zhang: Investigation, Validation. Juan Luo: Methodology, Formal analysis. Hong Chuan Fu: Conceptualization, Methodology. Li Shen: Conceptualization. Hong Qun Luo: Conceptualization, Resources, Project administration, Writing – review & editing. Nian Bing Li: Supervision, Project administration, Data curation, Funding acquisition.

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.

Acknowledgement

This work was financially supported by the National Natural Science Foundation of China (No. 21675131) and the Natural Science Foundation of Chongqing (No. cstc2020jcyj-zdxmX0003).

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