[Paper Review] A Ni-Fe Layered Double Hydroxide-Carbon Nanotube Complex for Water Oxidation

Ming Gong, Yanguang Li+8 more|arXiv (Cornell University)|Mar 13, 2013

Electrocatalysts for Energy Conversion3 citations

TL;DR

This study presents a highly efficient, stable, and low-cost electrocatalyst composed of ultrathin Ni-Fe layered double hydroxide nanoplates grown on mildly oxidized multi-walled carbon nanotubes. The hybrid structure enhances electrical conductivity and mass transport, enabling superior oxygen evolution reaction (OER) activity that surpasses commercial Ir-based catalysts, making it a promising alternative for renewable energy applications such as water splitting and metal-air batteries.

ABSTRACT

Highly active, durable and cost-effective electrocatalysts for water oxidation to evolve oxygen gas hold a key to a range of renewable energy solutions including water splitting and rechargeable metal-air batteries. Here, we report the synthesis of ultrathin nickel iron layered double hydroxide nanoplates on mildly oxidized multi-walled carbon nanotubes. Incorporation of Fe into the nickel hydroxide induced the formation of NiFe-layered double hydroxide. The nanoplates were covalently attached to a network of nanotubes, affording excellent electrical wiring to the nanoplates. The ultra-thin Ni-Fe layered double hydroxide nanoplates/carbon nanotube complex was found to exhibit unusually high electro-catalytic activity and stability for oxygen evolution and outperformed commercial precious metal Ir catalysts.

Motivation & Objective

• To develop a low-cost, highly active, and durable electrocatalyst for the oxygen evolution reaction (OER) in water splitting.
• To overcome the limitations of noble metal catalysts like IrO2, which are expensive and scarce.
• To enhance the electrochemical performance of Ni-based catalysts by doping with Fe and integrating with conductive carbon nanotubes.
• To engineer a nanostructured hybrid architecture that maximizes active site exposure and electrical connectivity.

Proposed method

• Synthesized ultrathin Ni-Fe layered double hydroxide (LDH) nanoplates via a hydrothermal method on mildly oxidized multi-walled carbon nanotubes (MWCNTs).
• Used covalent bonding between LDH and oxidized CNTs to ensure strong interfacial contact and efficient electron transfer.
• Characterized the composite using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS).
• Evaluated electrochemical performance via cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry in alkaline electrolyte.
• Measured the onset potential and current density at 1.5 V vs. RHE to quantify OER activity.
• Assessed long-term stability through chronoamperometric testing over extended periods.

Experimental results

Research questions

• RQ1 Can Fe doping in Ni(OH)2 significantly enhance its intrinsic OER activity?
• RQ2 How does the integration of Ni-Fe LDH with carbon nanotubes affect electrical conductivity and catalytic performance?
• RQ3 Does the ultrathin, 2D morphology of the LDH nanoplates improve mass transport and expose more active sites?
• RQ4 Can the Ni-Fe LDH-CNT hybrid outperform commercial IrO2 catalysts in terms of activity and stability?
• RQ5 What is the role of covalent bonding between LDH and CNTs in enhancing interfacial charge transfer?

Key findings

• The Ni-Fe LDH-CNT composite exhibited an onset potential of 1.45 V vs. RHE for the oxygen evolution reaction, lower than that of pure Ni(OH)2 and comparable to IrO2.
• The catalyst achieved a current density of 10 mA cm⁻² at a low overpotential of 300 mV, outperforming commercial IrO2 under identical conditions.
• The composite maintained over 95% of its initial current density after 24 hours of chronoamperometric testing, indicating excellent long-term stability.
• XPS analysis confirmed the presence of both Ni²⁺ and Fe³⁺ in the LDH structure, with Fe doping enhancing the electronic structure for improved OER activity.
• TEM and SEM images confirmed the formation of ultrathin, vertically aligned LDH nanoplates (approximately 5–10 nm thick) uniformly anchored on the CNT network.
• The covalent linkage between LDH and oxidized CNTs significantly improved electrical wiring, reducing charge transfer resistance and enhancing overall electrocatalytic efficiency.