Role of Iron in Ni-Fe Alloy Nanoparticles for Electrocatalytic Ethanol to Acetic Acid Conversion

Electrooxidizing ethanol to value-added acetic acid is a typical case of replacing the oxygen evolution reaction to promote the cathodic hydrogen evolution reaction and save energy.This paper proposes a colloidal strategy for preparing nickel-iron bimetallic alloy nanoparticles (NPs) as efficient electrocatalysts for ethanol electrooxidation in alkaline media. In a 1.0 M potassium hydroxide (KOH) solution containing 1.0 M ethanol, the nickel-iron alloy NPs can provide a current density of 100 mA·cm−2 at a voltage of only 1.5 V versus the reversible hydrogen electrode (RHE), which significantly outperforms other electrocatalysts in similar systems. Under this applied potential, continuous testing for 10 hours showed that the electrode could average 0.49 mmol·cm−2·h−1 of acetic acid production, with a Faradaic efficiency of ethanol conversion to acetic acid of 80%. This paper employs a series of spectroscopic techniques to explore the electrocatalytic process and analyze the electrolyte. Additionally, density functional theory (DFT) calculations indicate that iron in the alloy NPs significantly enhances conductivity and electron transfer, alters the rate-determining steps, and lowers the energy barrier in the reaction pathway of converting ethanol to acetic acid.

01 Research Background and Objectives

The electrooxidation of ethanol is of significant importance in energy conversion and storage.

The study aims to develop efficient electrocatalysts for ethanol electrooxidation, enhancing current density and Faradaic efficiency for the conversion of ethanol to acetic acid.

02 Synthesis of Ni-Fe Alloy NPs

Ni-Fe alloy NPs were synthesized using a colloidal strategy, controlling the alloy composition by adjusting the atomic ratio of Ni/Fe precursors.

Alloy NPs with different Ni/Fe ratios, such as Ni3Fe0.33 and Ni3Fe0.75, were synthesized.

03 Material Characterization

The crystal structure and morphology of Ni-Fe alloy NPs were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM).

X-ray photoelectron spectroscopy (XPS) analysis revealed the elemental states and composition on the alloy surface.

04 Electrochemical Performance Evaluation

In a 1.0 M KOH solution, Ni-Fe alloy NPs achieved a current density of 100 mA·cm-2 at 1.5 V vs. RHE, surpassing other similar system electrocatalysts.

During continuous testing for 10 hours, the Ni-Fe alloy electrode averaged 0.49 mmol·cm-2·h-1 of acetic acid production, with a Faradaic efficiency of 80% for ethanol to acetic acid conversion.

Role of Iron in Ni-Fe Alloy Nanoparticles for Electrocatalytic Ethanol to Acetic Acid Conversion

05 In-Situ Infrared Spectroscopy (IRAS) Analysis

IRAS was used to detect reaction intermediates during the electrocatalytic process.

Infrared adsorption bands related to acetic acid were detected, confirming the electrocatalytic conversion of ethanol to acetic acid.

06 Density Functional Theory (DFT) Calculations

DFT calculations revealed the impact of iron doping in Ni-Fe alloys on the mechanism of ethanol electrooxidation.

Iron doping facilitated the phase transition of Ni(OH)2 to NiOOH, enhancing the adsorption and conversion efficiency of ethanol.

07 Illustrated Guide

Role of Iron in Ni-Fe Alloy Nanoparticles for Electrocatalytic Ethanol to Acetic Acid Conversion

08 Discussion of Reaction Mechanism

The electrochemical conversion of ethanol to acetic acid involves the adsorption and desorption of multiple intermediates, including CH3CH2OH, CH3CH2O, CH3CHO, CH3CO, and CH3COOH.

DFT calculations indicate that iron doping reduces the energy barrier for ethanol adsorption and initial hydrogenation steps, while altering the rate-limiting steps.

09 Conclusion

This paper synthesized Ni-Fe alloy nanoparticles through a colloidal strategy, serving as efficient electrocatalysts for ethanol electrooxidation in alkaline media.
Ni-Fe alloy NPs exhibit excellent electrochemical performance, achieving high current densities at low potentials and producing high yields of acetic acid.
DFT calculations reveal the influence of iron doping on the mechanism of ethanol electrooxidation, providing theoretical guidance for designing more efficient electrocatalysts.
Moreover, this study offers new insights for replacing the oxygen evolution reaction to promote the cathodic hydrogen evolution reaction and save energy.

This article is provided by the Hydrogen Energy Research Assistant.

Original link:

https://www.sciopen.com/article/10.1007/s12274-023-6049-4

Role of Iron in Ni-Fe Alloy Nanoparticles for Electrocatalytic Ethanol to Acetic Acid Conversion

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