Dear Abhijit,

welcome,

i will give a conceptual answer of your question:

It is so that the electrolyte acts a hole transport layer conducting holes to the electrode. Therefore one needs a metal which have a Fermi level above the level of the electrolyte. It must act as an ohmic contact to the electrolyte with low interface resistance. As an example of efficient counter electrode is using Pt nano particles.

Best wishes

You can used Aluminium.

you can use Pt or graphene thin film as an electrode in PECs

Others may used nanoparticles such as Ag, Au, C60, ......etc

as mentioned by Dr Makhlouf and Dr Zekry, ultra thin film Pt layer might work best as counter electrode. Nonetheless, nano carbon materials, e.g., graphene and CNTs or composite of boths, were proven to work as efficient as Pt counter electrode does.

Thanks Dr Ali Farmani, Prof Abdelhalim Zekry , Prof Beddiaf Zaidi , Prof M M Makhlouf , Dr Ruri Agung Wahyuono for the suggestions. it will definately help me in research.