Influence of Temperature on The Activation/Deactivation Behavior of Nickel Oxide Nanoparticles Modified GC Electrode Towards The Oxygen Evolution Reaction Doha M. Sayed, Gumaa A. El-Nagar, Mohamed S. El-Deab, Bahgat E. El-Anadouli Department of Chemistry, Faculty of Science, Cairo University, Cairo, Egypt. *corresponding author: E-mail address: :
[email protected] (M. S. El-Deab),
Abstract This paper addresses the effect of temperature (T) on the electrocatalytic activity of nickel oxide nanostructured modified glassy carbon electrode (nano-NiOx/GC) towards the oxygen evolution reaction(OER). That is, increasing T results in a significant enhancement of the catalytic activity probed by: (i) a favorable negative shift of the onset potential (EOnset) of the OER, and (ii) an increase of the OER current at a particular potential. This enhancement may be explained by: (i) an increase of the amount of the active phase of NiOx participating in the OER, (ii) a decrease of the average particle size of nanoNiOx (reduced from ca. 150 nm at 25 ºC to ca. 30 nm at 60ºC) which results in a significant increase of the electroactive surface area, (iii) an observable decrease of the size of O2 bubbles attached to the surface of nano-NiOx together with an increase of their rate of detachment, and (iv) a decrease of the ohmic potential drop with a reduction of charge transfer resistance of the OER. Regeneration of the lost activity upon prolonged electrolysis at elevated temperatures could be achieved.
Experimental
❑ Nickel oxide nanostructured (nano-NiOx) is electrodeposited onto the GC electrode in two sequential steps; the first involves electrodeposition of nickel from an aqueous solution (pH 4.0) containing 1 mM Ni(NO3)2. The second step is the electrochemical passivation of the electrodeposited metallic. ❑ Electrochemical measurements are performed in a three-electrode two compartment glass cell, using an EG&G potentiostat (model 273A). Linear sweep voltammetry (LSV) and chronopotentiometry are used to evaluate the electrocatalytic activity and stability at different temperatures. EIS measurements are performed in the frequency range from 10 mHz–100 kHz at open circuit potential and 0.77 V to estimate the solution resistance, Rs and charge transfer resistance (Rct) during the OER. (FE-SEM, QUANTA FEG 250) coupled (EDX) unit and XRD (PANalytical, X’Pert PRO), operated to characterize the examine electrode.
Results and discussion I- Material Characterizations I.1. SEM characterization:
I.2. EDS and XRD characterization:
Figure 2. (A) EDS analysis of nano-NiOx/GC (B) XRD pattern of nano-NiOx/GC electrode passivated at various temperatures
II- Electrochemical Characterizations
V- Effect of Temperature on Bubble Size
Figure 6. Bubble size images formed on nano-NiOx/GC electrode during E-t measurement at various temperatures after 3 min of continuous electrolysis at 7 mA cm-2.
IV- Activation-Deactivation behavior at 40 OC
Figure 3. CVs obtained at GC and nano-NiOx/GC electrode at different temperatures in 0.5 M KOH. Potential scan rate = 200 mVs-1.
III- Electrocatalytic activity toward OER
Figure 4. LSVs of unmodified GC at 25ºC and nano-NiOx/GC electrode in 0.5 M KOH at various temperatures with scan rate 20 mVs-1.
IV- Effect of T on the charge transfer resistance (Rct) and the resistance of solution (Rs) .
Figure 7. (A) LSVs obtained at 40oC of nano-NiOx/GC electrode in 0.5 M KOH at 20 mVs-1. (B) LSVs of deactivated electrode, after activation by different number CVs, and fresh electrode. (Inset B: CVs of the mentioned electrode at scan rate 200 mVs-1 in 0.5 M KOH at 500 mVs-1 after different no. of cycles.
Conclusion
Figure 1. FE-SEM images of metallic nickel and nickel oxide passivated at various temperatures. RESEARCH POSTER PRESENTATION DESIGN © 2012
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Figure 5. Nyquist plots for nano-NiOx/GC electrode measured at 0.77 V in 0.5 M KOH at various temperatures. (Inset: Nyquist plots at open circuit potential).
➢The electrodeposition of nano-NiOx on GC surface resulted in a significant favorable negative shift of the OER onset potential. ➢Electrocatalytic activity of nano-NiOx/GC electrode increases as the temperature increases,and this may be due to : (i) decrease of the average particle size of nano-NiOx and hence the exposed electroactive surface area increases, (ii) a reduction of the O2 bubble size and increase of its rate of detachment from the nanoNiOx/GC surface, (iii) decreases the OER charge transfer and reduces the ohmic overpotential. ➢ Operating at elevated temperatures causes a rapid loss of activity although the nano-NiOx/GC electrodes shows a momentarily marked increase of the OER rate.
