Key Takeaways & Executive Findings
- •• A simple one-step high-temperature pyrolysis method fabricates hierarchical NiX@CNT catalysts with tunable non-metallic element doping. • Twelve catalyst variants were prepared by temperature adjustment, enabling systematic optimization of HER and OER activity. • Ni(NO3)2@CNT-900 demonstrates superior bifunctional performance with low overpotentials (145 mV for HER, 300 mV for OER at 10 mA/cm²). • The optimized catalyst exhibits excellent durability in alkaline electrolyte, highlighting its potential for practical water splitting.
Abstract
Developing efficient, durable, and precious metal-free electrocatalysts is currently a huge challenge. In this article, through a simple one-step high-temperature pyrolysis method, by incorporating various non-metallic element atoms, we prepared four different NiX(X=Cl2, (CH3COO)2, (NO3)2, SO4)@CNT catalysts. Additionally, by adjusting the temperature, these four materials were expanded into twelve catalyst materials for comparative optimization of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity. Ultimately, Ni(NO3)2@CNT-900 typically exhibits superior OER and HER activity. In 1 mol/L KOH solution with a current density of 10 mA/cm2, the overpotentials of HER and OER of Ni(NO3)2@CNT-900 are only 145 mV and 300 mV, respectively. Furthermore, the Ni(NO3)2@CNT-900 shows excellent durability in both HER and OER.
1. Introduction
The requirement for sustainable, pollution-free energy has drawn a lot of attention. Hydrogen is currently being focused on due to its high energy density and minimum carbon emissions during combustion [1−4]. Electrochemical water splitting for hydrogen production is an efficient approach for the storage of intermittent energy sources. However, the electrochemical water splitting is sluggish and usually occurs under high overpotentials [5−8]. Therefore, the electrocatalyst with excellent performance is very important to reduce the overpotential of hydrogen evolution reaction (HER) and oxygen evolution reaction. Currently, precious metal Pt is considered the most active catalyst toward the HER, while precious IrO2 and RuO2 are the most active catalysts toward the oxygen evolution reaction (OER). However, their high cost and scarcity seriously hinder their practical application. Therefore, it is highly desirable to exploit inexpensive and earth-abundant HER and OER electrocatalysts [9−13].
Among various promising alternatives, nickel-based materials have been explored as ideal and efficient non-noble metal electrocatalysts. Especially, nickel-based catalysts, including oxides [14, 15] and hydro(oxy)oxides [16] for the OER, and sulfides [17, 18], phosphides [19], carbides [20], and nitrides [21] for the HER have been investigated, owing to their facile electronic structure regulation. However, most of the above electrocatalysts have the strong bonding strength of OOH*/OH* intermediates with metal active substances, poor electronic conductivity, and instability in direct contact with highly alkaline electrolytes, leading to low activity. Modifications of these materials’ physical and chemical properties have been investigated to further improve the electrochemical stability of nickel compounds.
The strong metal-support interactions can effectively enhance the stability of the catalyst, as well as prevent the aggregation of loaded nanoparticles (NPs) and facilitate the electron transfer process [22, 23]. Recently, the coating of carbon frames has been beneficial in improving the activity and stability of transition metal-based catalysts [24]. Carbonaceous materials, such as porous activated carbon, graphene, carbon nanofibers, and carbon nanotubes (CNTs), showed good electrical conductivity, large surface area, and good chemical durability properties, which makes them excellent coating materials for various catalysts [25−28]. Carbon nanotubes have better electrical conductivity and mechanical strength among these carbon materials due to their one-dimensional characteristics and act as an efficient coating material for catalysts [29−42]. For example, Ru/Co-NCNTs [31], N-D-HCNT@pNi-Fe NPs [32], and Co/CNFs [33] exhibit excellent HER performance. Mn/V/N/S-doped-MWCNT [35], Fe0.6Co0.4-P@O [36], Ni2PNPs/NP-CNTs-850 [37], Fe/PVP-M [38], NiFeP@NC/CNT [39], CNTCo185H2 [40], Ni-Fe-P@CNTs-CC (carbon cloth) [41], and NiFeLDH/CNTs [42] exhibit good OER activities. However, the carbon frame-coated nickel-based bifunctional catalysts that can catalyze the HER and OER simultaneously in the same electrolyte have rarely been reported. Herein, we report a simple method by pyrolysis of dicyandiamid...
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ZHANG Bai-qing, YIN Zhuo-xun, MA Xin-zhi, ZHOU Yang, LI Jin-long, WANG Yu-ping, WAN Li-juan, MA Zhan-chun (2025). In situ fabrication of hierarchical NiX@CNT: An efficient bifunctional electrocatalyst for water splitting. Journal of Central South University. https://doi.org/10.1007/s11771-025-5981-8
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Frequently Asked Questions
What is the Ni(NO3)2@CNT-900 catalyst?
Ni(NO3)2@CNT-900 is a nickel-based catalyst synthesized by a one-step high-temperature pyrolysis method, where nickel nitrate is decomposed and supported on carbon nanotubes at 900 °C. It acts as an efficient bifunctional electrocatalyst for both the hydrogen evolution reaction and oxygen evolution reaction in alkaline media.
How were the NiX@CNT catalysts prepared?
The catalysts were prepared by a simple one-step high-temperature pyrolysis method using dicyandiamide and different nickel salts (chloride, acetate, nitrate, sulfate). By varying the pyrolysis temperature, a library of twelve catalysts was obtained for comparative optimization.
What are the overpotentials for HER and OER reported in the study?
In 1 mol/L KOH solution at a current density of 10 mA/cm², Ni(NO3)2@CNT-900 exhibits overpotentials of 145 mV for the hydrogen evolution reaction and 300 mV for the oxygen evolution reaction, demonstrating superior performance.
Why are non-precious metal catalysts important for water splitting?
Precious metals like Pt, IrO2, and RuO2 are highly active but expensive and scarce. Non-precious metal catalysts, such as nickel-based compounds, offer a cost-effective and earth-abundant alternative for large-scale hydrogen production via electrochemical water splitting.
What is the significance of using carbon nanotubes in the catalyst design?
Carbon nanotubes provide excellent electrical conductivity, high surface area, and mechanical strength, which enhance electron transfer and prevent nanoparticle aggregation. This leads to improved catalytic activity and stability of the nickel-based catalysts.
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