Dear Winnie Chang ,

what is the substrate and the origin[1] (and pretreatment?) of your WE (electrodes' material(s)[2,3]) ?

1. More common copper oxides are CuO [Cu is in oxidation state: +2 ] and Cu2O [Cu is in oxidation state: +1]. However, there are uncommon ... copper oxides ...

2. Porous Texture of CuO Prepared from Copper Oxalate Precursor https://journals.sagepub.com/doi/pdf/10.1260/026361706780154374

3. Experimental and theoretical investigation of the electronic structure of Cu2O and CuO thin films on Cu(110) using x-ray photoelectron and absorption spectroscopy https://www.researchgate.net/publication/323461462_Thermal_conversion_of_Cu4O3_into_CuO_and_Cu2O_and_the_electrical_properties_of_magnetron_sputtered_Cu4O3_thin_films

Greatly appreciate your response! The substrate is copper sheet and pretreatment is basic cleaning, such as acid cleaning, aceton and then followed by IPA and DI water rinse.

Dear Prof Ioannis,

Thanks for shaing the link! The copper oxides in my case is sintered copper that is formed on a Cu sheet at a low temperature. The sintered copper provide a porous platform where oxide is formed through certain oxidation.

Dear Prof Ioannis,

Thanks for shaing the links! In my case, copper particles are sintered on a Cu sheet at a low temperature. The sintered copper provides a porous platform where oxides are formed through certain oxidation to serve the purpose as supercapacitor active material.

Dear Winnie Chang ,

you might avoid such negative side-effects, by hiding/protecting

a) 'the other' (back) side of the bare-metallic[1,2] (Cu-) substrate.

Also, hide/protect

b) the WE from exposure to any environmental room (or sun?) light (activating possible water splitting[3-5]) by (photo-)covering[6] your cell.

1. paint/hide well (say, by paraffin wax, etc.), only the metallic Cu-substrate part, towards its' total protection from the electrolyte's exposition. https://paraffinwaxco.com/paraffin-wax/fully-refined-paraffin-wax/

2. https://en.wikipedia.org/wiki/Standard_electrode_potential_(data_page)

3. Room temperature synthesis of highly active Cu/Cu2O photocathode for photoelectrochemical water splitting https://www.researchgate.net/publication/306024720_Room_temperature_synthesis_of_highly_active_CuCu2O_photocathode_for_photoelectrochemical_water_splitting

4. Electrodeposition of Copper Oxides as Cost-Effective Heterojunction Photoelectrode Materials for Solar Water Splitting

https://www.mdpi.com/2079-6412/12/12/1839

5. Copper Oxide-Based Photocatalysts and Photocathodes: Fundamentals and Recent Advances https://www.researchgate.net/search.Search.html?query=Copper+Oxide-Based+Photocatalysts+and+Photocathodes%3A+Fundamentals+and+Recent+Advances&type=publication

6. cover well your (glassware?) cell (by Al-foil, etc.).

Dear Prof Ioanniss,

Deeply appreciate your advice and the shared info!

Right. The back side of the Cu sheet was protected from exposure to the electrolyte to avoid signal confusion with adhesive tape.

The sample was never exposed to sun light and was stored in a sealed container. The file as attached is how its CV curve looks like.

I saw papers about copper oxideds fabricated with sputtering technology may also have a sort of negative potential range. Why?

Thanks for your time & precious advice!

Dear Winnie Chang ,

can you remake, please, two CV (sets[1]) in the potential range: [-0.2V, +0.7V] ?

1. V-rates: a) 100mV/s, b) 1mV/s.

Dear Prof Ioannis,

Sorry for confusing you! The two sets are from same run, but just different cycles. The scan rate is 50mv/s. Thanks a lot for your time!!!! Best regards!