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. 2018 Jul 11;3(7):7745-7756.
doi: 10.1021/acsomega.8b00799. eCollection 2018 Jul 31.

Synthesis of Highly Efficient Bifunctional Ag/Co3O4 Catalyst for Oxygen Reduction and Oxygen Evolution Reactions in Alkaline Medium

Anchu Ashok  1 , Anand Kumar  1 , Md Abdul Matin  1 , Faris Tarlochan  1
Affiliations

Synthesis of Highly Efficient Bifunctional Ag/Co3O4 Catalyst for Oxygen Reduction and Oxygen Evolution Reactions in Alkaline Medium

Anchu Ashok et al. ACS Omega. .

Abstract

Ag/Co3O4 catalysts using three different modes of solution combustion synthesis were developed and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy to identify crystallite size, oxidation state, composition, and morphology. Cyclic voltammetry and linear sweep voltammetry measurements for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) confirm the bifunctionality of the electrocatalysts. The electrochemical evaluation indicates that a synergic effect between Ag and Co enhances the activity through the fast breaking of O-O bond in the molecular oxygen to enhance the reduction mechanism. The high content of cobalt (Co) in the catalyst Ag/Co3O4-12, synthesized by second wave combustion, improves the activity for ORR, and the reaction mechanism follows a 3.9 number of electron transfer in overall reaction. The kinetic and limiting current densities of Ag/Co3O4-12 are maximum when compared to those of other Ag/Co3O4 catalysts and are very close to commercial Pt/C. Moreover, the maximum current density of OER for Ag/Co3O4-12 makes it a promising candidate for various bifunctional electrocatalytic applications such as fuel cells and metal-air batteries.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
XRD pattern of three synthesis modes of Ag–Co using combustion synthesis.
Figure 2
Figure 2
(a) UV–visible absorption spectrum of monometallic and bimetallic Ag–Co. (b–d) Tauc plot to determine the optical band gap in Ag/Co3O4-11, Ag/Co3O4-12, and Ag/Co3O4-21.
Figure 3
Figure 3
FTIR absorbance spectrum of Ag/Co3O4 catalysts prepared using the SCS technique.
Figure 4
Figure 4
SEM images of the Ag–Co nanopowders synthesized using the SCS technique: (a) Ag/Co3O4-11, (b) Ag/Co3O4-12, and (c) Ag/Co3O4-21.
Figure 5
Figure 5
TEM images of the as-synthesized NPs and their corresponding lattice fringes at high magnification for (a,d) Ag/Co3O4-11, (b,e) Ag/Co3O4-12, and (c,f) Ag/Co3O4-21.
Figure 6
Figure 6
XPS spectra comparison for all the samples and the detailed study on individual elements: (a,b) Ag 3d, (c,d) Co 2p, and (e,f) O 1s.
Figure 7
Figure 7
CV for Ag/Co3O4-11/C, Ag/Co3O4-12/C, and Ag/Co3O4-21/C catalysts in (a) N2-saturated and (b) O2-saturated 1 M KOH electrolyte at 0.05 V s–1 in a wide potential range to demonstrate the ORR and OER performance. The arrow indicates the scan direction.
Figure 8
Figure 8
(a) Rotating disk electrode I–V polarization curve (potential V vs NHE) in O2-saturated 1 M KOH at 1600 rpm for different Ag–Co alloys synthesized with SCS at a scan rate of 5 mV s–1 (−0.6 to 1.2 V vs NHE), (b) LSV performance of Ag/Co3O4-12/C at different rotation rates from 1600 to 400 rpm 1 (−0.2 to 0.9 V vs NHE), (c) KL plot for ORR at 0.15 V (inset—bar plot shows the kinetic current density and the number of electron transfer in each catalyst), and (d) bifunctional ORR and OER performance of different catalysts.
Figure 9
Figure 9
Mass-transport-corrected Tafel plot for (a) ORR and (b) OER of various catalysts in 1 M KOH solution corresponding to the 1600 rpm LSV plot.
Scheme 1
Scheme 1. Stepwise Synthesis of Ag/Co3O4-12 Sample (Mode 2) Using the Solution Combustion Technique
See this image and copyright information in PMC

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