Dear Muhammad junaid Anjum , if OCP is not stable because The surface is not well polished and is your electrolyte aggressive (PH) and you can see is there release of hydrogen, for that you can increase agitation and add more time for that; I hope these suggestions can help you

Dear Muhammad

Before one can answer your question, you have to define what electrochemical system you are dealing with, i.e, materials of working electrode, & counter electrode, type of reference electrode , and the electrolyte solution, and the potential range in which you are recording the OCP.

As mentioned above, the material, elctrolyte, experimental set-up including positions and spacing of electrodes could influence the ocp. Moreover, there are some alloys of aluminum in specific electrolyte where ocp is not stable.

You have not indicated what the metal/environment combination is that you are looking at, which makes giving a definitive answer rather difficult. As has been indicated by other respondents, it is perfectly possible that the open circuit potential of the system you are looking at will never be perfectly stable, for example if the system is pitting. You have also not indicated what kind of electrochemical test you are wanting to perform, which also leaves respondents in the dark, but let us assume as you haven't indicated anything to the contrary that you are wanting to do a polarization scan. My advice would be that you should go ahead and run a sequence of tests and find out what is typical of your system and how the response may vary. Gradually, you will start to understand what the factors are that can affect your particular system - let's say temperature, pH, solution concentration, oxygen dissolution, the effectiveness of nitrogen purging, agitation, effect of inhibitor, presence of inclusions, grain structure, susceptibility to SCC, etc., etc. After a while you will start to understand when your experimental setup is 'OK' (i.e. representative of the system you are interested in) and when it is 'not OK' (i.e. there is some kind of extraneous influence that is affecting the exchange current density behaviour at the electrochemical interface. Then you can introduce deliberate perturbations to investigate how parameters you are interested in can affect the response of your primary metal/environment system.

Muhammad

Could you please, show how the potential fluctuate i.e range of mV also, how does your sample looks like does it waxed or do you cover its edges how big is it....is it home-made sample or standard one...........

Before beginning any set of measurements, I prefer to check your system (Potentiostat, Refere. and Aux) using ASTM G5 standard test method.

If everything is OK, let's check the metal/environment system which may will not be stable due to many reason such as homogeneity of surface, pH changes during test, high corrosion rate, change the corrosion type from uniform to localized......

good luck

i am working with Mg metal coated with Mg-Al LDH. my electrolyte is 3.5% NaCl, ref is SCE and Pt counter electrode

Admito que seja corrosão por picadas. Mas pode confirmar com observação da amostra ao SEM.