The Effect of an External Magnetic Field on the Electrocatalytic Activity of Heat-Treated Cyanometallate Complexes towards the Oxygen Reduction Reaction in an Alkaline Medium.

Barbara Zakrzewska,Marek Marcinek,Krzysztof Miecznikowski,Lidia Adamczyk

doi:10.3390/ma15041418

Abstract

This work focuses on the development of an electrocatalytic material by annealing a composite of a transition metal coordination material, iron hexacyanoferrate (Prussian blue) immobilized on carboxylic-acid-functionalized reduced graphene oxide. Pyrolysis at 500 °C under a nitrogen atmosphere formed nanoporous core–shell structures with efficient activity, which mostly included iron carbide species capable of participating in the oxygen reduction reaction in alkaline media. The physicochemical properties of the iron-based catalyst were elucidated using transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy, and various electrochemical techniques, such as cyclic voltammetry and rotating ring–disk electrode (RRDE) voltammetry. To improve the electroreduction of oxygen over the studied catalytic material, an external magnetic field was utilized, which positively shifted the potential by ca. 20 mV. The formation of undesirable intermediate peroxide species was decreased compared with the ORR measurements without an external magnetic field.

Highlights

The most challenging tasks facing humans are energy shortages and environmental pollution [1,2]
The results indicated the internal rate of heterogeneous charge transfer in the absence and presence of an external magnetic field
We prepared a non-precious iron electrocatalyst by calcining Prussian blue immobilized onto carboxylic-acid-functionalized reduced graphene oxide

Summary

Introduction

The most challenging tasks facing humans are energy shortages and environmental pollution [1,2]. Polymer electrolyte membrane fuel cells (PEMFCs) are one example of such devices, which use hydrogen or small organic compounds as the fuel, and oxygen as the oxidant, to produce electricity with water or CO2 as the major products [3]. Electrocatalytic oxygen reduction can be enhanced in two ways: either by using more active catalysts (e.g., new catalyst) or using external process intensifications using different type of energy. There is a need to develop new electrocatalysts for more efficient ORR that exhibit high selectivity toward the four-electron reduction of O2 to H2O, rather than to the two-electron reaction which produces undesirable H2O2. The scarce resources, high prices, and decreased activity of Pt in the presence of small organic compounds (crossover effect in applications towards alcohol fuel cells) make them difficult to use in commercial applications. It is still challenging to develop efficient non-precious metal or metal-free catalysts for ORR [10,11,12,13,14,15,16,17,18]

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Results

Conclusion