Binary and Ternary 3D Nanobundles Metal Oxides Functionalized Carbon Xerogels as Electrocatalysts toward Oxygen Reduction Reaction.

Abdalla Abdelwahab,Agustín F Pérez-Cadenas,Francisco Carrasco-Marín

doi:10.3390/ma13163531

Abdalla Abdelwahab, Agustín F Pérez-Cadenas + Show 1 more

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https://doi.org/10.3390/ma13163531

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Abstract

A series of carbon xerogels doped with cobalt, nickel, and iron have been prepared through the sol–gel method. The doped carbon xerogels were further functionalized with binary and ternary transition metal oxides containing Co, Ni, and Zn oxides by the hydrothermal method. A development in the mesopore volume is achieved for functionalized carbon xerogel doped with iron. However, in the functionalization of carbon xerogel with ternary metal oxides, a reduction in pore diameter and mesopore volume is found. In addition, all functionalized metal oxides/carbon are in the form of 3D nanobundles with different lengths and widths. The prepared samples have been tested as electrocatalysts for oxygen reduction reaction (ORR) in basic medium. All composites showed excellent oxygen reduction reaction activity; the low equivalent series resistance of the Zn–Ni–Co/Co–CX composite was especially remarkable, indicating high electronic conductivity. It has been established that the role of Zn in this type of metal oxides nanobundles-based ORR catalyst is not only positive, but its effect could be enhanced by the presence of Ni.

Highlights

The negative effects that fossil combustion has had upon the environment has created a demand to develop and implement alternative clean energy sources [1,2]
Brunauer-Emmett-Teller, BET equation was applied to the obtained isotherms to calculate their corresponding surface areas [35]
The results show that the electrochemical performance toward oxygen reduction reaction (ORR) is higher for cobalt-doped carbon xerogels (Co-CX) followed by samples doped with iron (Fe) and nickel (Ni), which is in good agreement with previously published work [31,44]

Summary

Introduction

The negative effects that fossil combustion has had upon the environment has created a demand to develop and implement alternative clean energy sources [1,2]. The high cost per unit energy delivered reduces the use of PEM fuel cells at a large scale and introducing to market. This problem can be solved either by reducing the used fuel cost, typically H2 , or searching for an electrocatalyst that enhances the overall efficiency and energy generation. The fuel cell half reactions are an anodic hydrogen oxidation reaction (HOR) and cathodic oxygen reduction reaction (ORR). The overpotential for HOR is considered as negligible, while for ORR, it requires high energy to initiate the reaction due to large kinetic inhibition. The oxygen reduction reaction (ORR) is considered as the rate-determining step, and reducing its overpotential will enhance the fuel cell efficiency. The four-electron transfer pathway is the favored one, because it forms the hydroxyl species rather than peroxide [5,6], which causes membrane

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