Key Takeaways & Executive Findings
- •• CoFe bimetallic hydroxide nanosheets (CoFe BMH NSHs) exhibit superior oxygen evolution reaction (OER) activity with an overpotential of 282 mV at 100 mA·cm−2 and an overall water splitting voltage of 2.05 V. • The nanosheet morphology provides the largest electrochemically active surface area among the four synthesized morphologies, as evidenced by the highest double-layer capacitance (Cdl). • In situ Raman spectroscopy reveals that metal oxyhydroxide (MOOH) is the active species during OER, and its formation is irreversible. • This systematic study offers a design guideline for optimizing catalyst morphology to enhance performance in water splitting applications.
Abstract
CoFe bimetallic hydroxides (CoFe BMHs) find wide applications as excellent catalysts in the field of water splitting. However, no study has systematically investigated the influence of the morphologies of CoFe BMHs on catalyst performance. In this study, CoFe BMH nanoflowers (CoFe BMH NFs), CoFe BMH nanosheets (CoFe BMH NSHs), CoFe BMH nanorods (CoFe BMH NRs), and CoFe BMH nanospheres (CoFe BMH NSPs) were prepared on nickel foam via a hydrothermal method. CoFe BMH NSHs exhibited the most beneficial catalytic activity. At a current density of 100 mA·cm−2, its overpotential for oxygen evolution reaction (OER) was 282 mV, and the overall water splitting voltage was 2.05 V. The double-layer charging capacitance (Cdl) value of CoFe BMH NSHs was the largest in CoFe BMHs, which proves that CoFe BMH NSHs have the largest active area. Furthermore, the active site in the OER process was metal oxyhydroxide (MOOH) through in situ Raman characterization, and the generation of the active substance was an irreversible process. This work provides important insights into the design of catalyst morphologies and offers valuable guidelines for the enhancement of the performance of other catalysts.
1. Introduction
As a clean energy source, hydrogen energy can considerably reduce greenhouse gas emissions and contribute to combating climate change [1–3]. Various water splitting methods are considered the most environmentally friendly hydrogen production method [4]. In the overall water splitting process, the four-electron process of anode oxygen evolution reaction (OER) occurs slowly and consumes most of the energy input, which determines the energy consumption of the entire reaction [5–6]. Although precious metal catalysts (e.g., IrO2/RuO2) exhibit excellent activity in OER [7–8], they are costly. Currently, large-scale electrolyzers in industrial settings mainly use nickel-based catalysts, such as pure nickel mesh or nickel foam, that possess excellent conductivity, high-volume porosity, and good mechanical properties. However, further increasing the number of catalytic sites solely through structural optimization of nickel mesh or foam presents a challenge. Optimization, such as the deposition of catalysts with a high specific surface area and catalytic activity on substrates, can be performed at a microscopic scale [9–12].
Transition metal hydroxides are well-known electrocatalysts due to their easy-to-obtain raw materials, adjustable chemical composition, superior activity, and stability [13–15]. CoFe bimetallic hydroxides (CoFe BMHs) exhibit excellent OER performance under alkaline conditions [16–18]. However, the low electrical conductivity of CoFe BMHs hinders the expression of catalytic activity [19]. Growing CoFe BMHs on a nickel foam substrate is an effective means of addressing this issue [20–21]. In addition, the microstructural morphology of the catalyst influences the active sites and intrinsic activity. Although researchers have prepared CoFe BMH nanoflowers (CoFe BMH NFs) [22–23], CoFe BMH nanosheets (CoFe BMH NSHs) [24–25], and CoFe BMH nanorods (CoFe BMH NRs) [26] using various methods, no systematic investigation has been conducted on the relationship between the morphology preparation of CoFe BMHs and their catalytic performance.
Herein, we utilized a one-step hydrothermal method to prepare CoFe BMH NFs, CoFe BMH NSHs, CoFe BMH NRs, and CoFe BMH nanospheres (CoFe BMH NSPs) on the nickel foam surface. The porous structure of the nickel foam not only facilitated the transfer of substances during the reaction process but also compensated for the poor conductivity of CoFe BMHs. Physical characterization and electrochemical testing revealed that CoFe BMH NSHs exhibited the most superior catalytic performance. CoFe BMH NSHs demonstrated an overpotential of 282 mV for OER at a current density of 100 mA·cm−2. Furthermore, the surface structural changes in CoFe BMH NSHs during OER were measured via in situ Raman spectroscopy.
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Liming Yang, Yuanbo Cao, Linsong Wang, Tao Yang, Kang Wang, Enhui Wang, Xiangtao Yu, Hongyang Wang, Kuo-Chih Chou, Xinmei Hou (2025). Synthesis of various morphologies of CoFe bimetallic hydroxides for enhanced oxygen evolution reaction performance. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3076-4
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Frequently Asked Questions
What is the optimal morphology of CoFe bimetallic hydroxides for oxygen evolution reaction?
CoFe bimetallic hydroxide nanosheets (CoFe BMH NSHs) exhibit the best OER performance, with an overpotential of 282 mV at 100 mA·cm−2 and the largest electrochemically active surface area.
How were the different morphologies of CoFe bimetallic hydroxides synthesized?
The morphologies (nanoflowers, nanosheets, nanorods, and nanospheres) were prepared on nickel foam via a one-step hydrothermal method by adjusting synthesis conditions.
What is the active species during the oxygen evolution reaction for CoFe bimetallic hydroxides?
In situ Raman spectroscopy identified metal oxyhydroxide (MOOH) as the active species, and its formation is irreversible.
Why is the nanosheet morphology more beneficial for OER?
The nanosheet morphology provides a larger electrochemically active surface area, as indicated by the highest double-layer capacitance (Cdl), which enhances catalytic activity.
What is the significance of this study for catalyst design?
This study systematically investigates the influence of morphology on catalytic performance, providing guidelines for designing efficient catalysts for water splitting and other applications.
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