JIYI

hi, i am new here. Thx for having this forum. i am learning about oxygen measurement device and i find it difficult to understand about clarck electrode. i don't understand why does clarck electrode need an external power source? i did find a literature that answer this,but it made me more confuse. it says " the electrode potentials of the anode and cathode produce a small voltage difference between them which opposes the flow of electrons from anode to cathode. This is because the silver anode is electropositive relative to the cathode. A polarizing voltage supply of 0.6 Volts is used, which removes electrons from the anode and supplies them to the cathode." now, i don't understand: 1.i don't understand why the small voltage difference between them opposes the flow of electrons? 2.why does silver anode is more postitve than the cathode?(is it because the anode has given its electrons to cathode)? 3.why is it not like that with glavanic fuell cell? sorry for long post and probably a stupid question. i am actually a physician in my country and i have never touch chemistry again for some time..please bear with me..and please help..thz u with regards,Jiyi