Zinc oxide

Oxidation reduction potential

Administrative data

Endpoint:

oxidation reduction potential

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

It was indicated by the study director that, the assignment is speculative in nature, as the Pourbaix diagram is a potential-pH diagram and is a map of thermodynamic possibilities. The Pourbaix diagram may well identify the lowest energy state of Zn but the exact speciation may not exist as the corresponding redox reaction may not be favoured for kinetic reasons. Therefore the reliable of the study could not be assigned.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2010

Report date:

2010

Materials and methods

Principles of method if other than guideline:

Cyclic voltammetry. Cyclic voltammetric experiments were performed using Autolab PGSTAT 12 potentiostat, equipped with a PC for electrochemical measurement. A conventional three electrode cell was employed throughout the experiments with: NM electrode as the working electrode (WE), Hg/HgO as a reference (RE) and platinum electrode as the counter electrode (CE). Prior to use the Hg/HgO reference electrode was calibrated against a saturated calomel electrode (-149 mV against a SCE). Cyclic voltammograms were acquired after exposure of the working electrode to the test solution (100 ml) in a glass filled cell; electrical connection to the working electrode was achieved by connecting a small mounted crocodile clip to the silver gauze that was attached to the WE. The WE was immersed so that approximately two thirds of the disc (and no silver) was exposed to the solution. Cyclic voltammetry (5 cycles) was undertaken at a rate of 100 mV/s, between the potentials of 0.7 V and –1.8 V.

GLP compliance:

no

Test material

Test material information

Constituent 1

Test material form:

solid: nanoform

Details on test material:

electrode made from bulk NM

Results and discussion

Any other information on results incl. tables

Figure shows a typical cyclic voltammogram (C-V) of PROSPEcT Z-COTE ZnO (BASF,) electrode in seawater at a scan rate of 100 mV/s. Results show two redox processes that are taking place, which will be referred to as “Redox 1” and “Redox 2”. Each redox reaction consists of two half-reactions i.e. for oxidation and reduction reactions and these correspond to the oxidation peak and reduction peak in the C-V plot. From these values, a mid-point potential was reported, which gave an indication of the corresponding redox potential value; the information from the C-V plot is summarised on Table 10. It is evident from the C-V plot that the redox potential values reported here should be treated with caution as:

A) Peaks were very broad, so numbers are only approximate

B) Peak-peak separation was large, indicating that the processes were not fully reversible

A summary of reduction and oxidation potential and the corresponding redox potential values for Z-COTE ZnO electrode 

PROSPEcT Z-COTE ZnO electrode (BASF, Germany), batch number ZC250#37#RP.
	Reduction peak potential (anodic process) (mV)	Oxidation peak potential (cathodic process) (mV)	Redox potential (mV)	Redox system
Redox 1	-1550	-980	-1265	ZnO/Zn
Redox 2	-130	400	135	?

 

Applicant's summary and conclusion

Conclusions:

Results showed that redox 1 to ZnO/Zn was ascribed attentively, as interpreted from the Pourbaix diagram. However, the assignment was speculative in nature, as the Pourbaix diagram was a potential-pH diagram and was a map of thermodynamic possibilities. The Pourbaix diagram may well identified the lowest energy state of Zn but the exact speciation may not existed as the corresponding redox reaction may not was favoured for kinetic reasons. Currently, the assignment of Redox 2 had been ascribed and there is a need to conduct a thorough review of the literature for interpretation of Redox 2.

Executive summary:

A study was conducted by NPL, 2010 using Cyclic voltammetric method to determine the redox potential of NM‑110. Results show two redox processes that are taking place, which was referred to as “Redox 1” and “Redox 2”. Each redox reaction consists of two half-reactions i.e. for oxidation and reduction reactions and these correspond to the oxidation peak and reduction peak in the C-V plot.

 

Furthermore it was indicated by the study director that the values should be treated with caution as:

a)        Peaks were very broad, so numbers are only approximate.

b)        Peak-peak separation was large, indicating that the processes were not fully reversible.