There are two factors affecting the CV shapes when loading of active material increases. Firstly, the resistance of the electrode would usually increase with loading more materials if the substrate area remains the same. The consequence is that the rectangular CV becomes sloped at both ends of the potential scan, and this distortion can lead to the recording of a sloped olive-shaped CV. Second, if the active material is in the form of fine powder, loading increase would enlarge significantly the actual electrode surface area whilst the geometrical area of the electrode looks similar. This may lead to adsorption and enrichment of some redox active impurities in the electrolyte onto the electrode, leading to additional current peaks.

As mentioned by Athanasios Papaderakis, there is also the chance that the accessibility to the electrode active sites will be relatively reduced when the loading becomes thicker. However, I do not think this will affect the CV shape except for the resistance induced distortion.

(Added on 08/09/2016. I thank those RG members who up-voted my answer above. I also notice a down-vote to my answer and hence would be grateful if the reason can be provided here as well.)

Dear Mohit,

As you might already know the effect of loading in both activity and surface area (which is directly related to activity) in such systems (like electrocatalysts and supercapacitors) is quite crucial. We have encountered similar situations in the past  while working on the synthesis of unsupported IrO2 nanocatalysts for oxygen evolution reaction (see attached figure where it is quite evident that an increase of catalyst loading leads to a suppression of surface processes electrochemical response and as a result to a decreased electrochemically active surface area). We have attributed the observed effect to a combination of accessibility/utilization - aggregation/coalescence phenomena of nanoparticles within catalyst mass. Thus we tried to find the optimum loading which would display the best utilization - surface area combination.     

I would recommend to perform experiments using a wide range of loadings in an attempt to find the "optimum" one for your system.

Hope that the above comments were a bit helpful to you. 

Best regards  

Thanks a lot.

yes of course, many factors can affect that.. one of critical factor, which is difficult to control it, is the crystallographic orientation.

please see our paper here: Noble-metal-modified glassy carbon electrodes for ethylene glycol oxidation in alkaline medium .

anyway, you did not mentioned what is the type or your materials and the way of loading.

There are two factors affecting the CV shapes when loading of active material increases. Firstly, the resistance of the electrode would usually increase with loading more materials if the substrate area remains the same. The consequence is that the rectangular CV becomes sloped at both ends of the potential scan, and this distortion can lead to the recording of a sloped olive-shaped CV. Second, if the active material is in the form of fine powder, loading increase would enlarge significantly the actual electrode surface area whilst the geometrical area of the electrode looks similar. This may lead to adsorption and enrichment of some redox active impurities in the electrolyte onto the electrode, leading to additional current peaks.

As mentioned by Athanasios Papaderakis, there is also the chance that the accessibility to the electrode active sites will be relatively reduced when the loading becomes thicker. However, I do not think this will affect the CV shape except for the resistance induced distortion.

(Added on 08/09/2016. I thank those RG members who up-voted my answer above. I also notice a down-vote to my answer and hence would be grateful if the reason can be provided here as well.)

Thanks a lot all of you.