Fabrication and Integration of Functionalized N-rGO-Ni/Ag and N-rGO-Ni/Co Nanocomposites as Synergistic Oxygen Electrocatalysts in Fuel Cells

Abstract

Fabrication of composites by developing simple techniques can be an efficient way to modify the desire properties of the materials. This paper presents a detailed study on synthesis of low cost and efficient nitrogen doped reduced graphene oxide nickle-silver (N-rGO-Ni/Ag) and nickel-cobalt (N-rGO-Ni/Co) nanocomposites as electrocatalysts in fuel cell using one-pot blended reflux condensation route. An admirable correlation in the structures and properties of the synthesized nanocomposites was observed. The Oxygen Reduction Reaction (ORR) values for N-rGO-Ni/Ag and N-rGO-Ni/Co calculated from the onset potential, using Linear Sweep Voltammetry (LSV), were found to be 1.096 and 1.146. While the half wave potential were determined to be 1.046 and 1.106, respectively, N-rGO-Ni/Ag and N-rGO-Ni/Co. The Tafel and bi-functional (ORR/OER) values were calculated as 76 and 35 mV/decade and 1.23 and 1.12 V, respectively, for N-rGO-Ni/Ag and N-rGO-Ni/Co. The lower onset and half wave potential, low charge transfer resistance (R_ct = 1.20 Ω/cm²) and internal solution resistance (R_s = 8.84 × 10^-1 Ω/cm²), lower Tafel values (35 mV), satisfactory LSV measurements and mass activity (24.5 at 1.056 V for ORR and 54.9 at 1.056 for OER) demonstrate the remarkable electrocatalytic activity of N-rGO-Ni/Co for both ORR and OER. The chronamperometric stability for synthesized nanocomposites was found satisfactory up to 10 h.

Keywords: N-doped reduced graphene oxide; bi-functional electrocatalysis; oxygen evolution reaction; oxygen reduction reaction.

Scheme 1

The schematic representation of the active sites and free functionalities of GO for counter part of metal precursor.

Figure 1

FTIR spectroscopy of (a) GO, (b) N-rGO, (c) N-rGO-Ni/Ag, and (d) N-rGO-Ni/Co.

Figure 2

X-ray diffraction analysis of (a) GO, (b) N-rGO, (c) N-rGO-Ni/Ag, and (d) N-rGO-Ni/Co.

Figure 3

Scanning Electron Micrographs of (a) GO, (b) N-rGO, (c) N-rGO-Ni/Ag and (d) N-rGO-Ni/Co.

Figure 4

Transmission electron microscopy of (a) N-rGO-Ni-Ag and (b) N-rGO-Ni-Co.

Figure 5

Brunauer–Emmet–Teller (BET) measurements of (a) GO, (b) N-rGO, (c) N-rGO-Ni/Ag and (d) N-rGO-Ni/Co.

Figure 6

X-ray photoelectron spectroscopy of (a) N-rGO-Ni/Co (b) C1s, (c) O1s, (d) Co2p, and (e) Ni2p.

Figure 7

X-ray photoelectron spectroscopy of (a) N-rGO-Ni/Ag (b) C1s (c) Ag3d.

Figure 8

Cyclicvoltammetry curves for bare glassy carbon (BGC) electrode and modified GC with N-rGO-Ni/Ag and N-rGO-Ni/Co.

Figure 9

LSV measurement in O₂-saturated 0.5 M KOH solution at 1200 rpm.

Figure 10

(a) Rotating disk voltammograms of N-rGO-Ni/Co inO₂-saturated 0.5 M KOH at different rotation rates, (b) Koutecky-Levich plot of N-rGO-Ni/Co at electrode potential of 0.3, 0.4, and 0.5 V.

Figure 11

ORR mass activity and specific activity (inset) of N-rGO-Ni/Ag and N-rGO-Ni/Co at different potential.

Figure 12

LSV curve of BGC, N-rGO-Ni/Ag, and N-rGO-Ni/Co for OER.

Figure 13

OER mass activity N-rGO-Ni/Ag and N-rGO-Ni/Co at different potential.

Figure 14

Tafel plots based on the LSV curve in 0.5 M KOH.

Figure 15

Chronoamperometric response recorded at applied potential of 1.36 V.

Figure 16

Oxygen electrode activities of both the catalysts within the range of potential for ORR and OER in O₂ saturated 0.5 M KOH electrolyte at 1200 rpm.

Figure 17

Nyquist plots for (a) N-rGO, N-rGO-Ni/Co and N-rGO-Ni/Ag (b) N-rGO-Ni/Co at 0.8 V, (c) 1 V, (d) 1.2 V and (e) proposed equivalent circuit.