Basically, ocp is depended on different conditions such as pH, saturated gas in electrolyte (deaerated or with oxygen) and others. The difference of saturated gas could be several hundreds of mV at elected pH. In my opinion it is possible to have oxidation/reduction in your system, as soon as the electrochemically conducted. As soon as your potential difference between cathode and anode is not zero you would measure current.

Best, 

Stefan

Most probably in the acidic condition the oxidation is predominant reactions. so the continuous hydrogen evolution and metal dissolution occurs,  this will give some colouration also. in the netural conditions the oxidation of metal and reduction as corrosion product will occur. The reduction of metal oxide into metal is possible at the cathodic reaction. refer some of the magnesium papers. their are no of reaction at the metal surface. but normally OCP condition with highly alkaline pH oxidation of metal ion and reduction as oxides are possible. Based on the Stefan Rudi the potential difference also having possibility to induce galvanic reaction at the metal surface. 

Which metal(s) do you have? Many metal oxides can oxidize or reduce depending on the redox potential of the solution (mainly aeration/deaeration) and depending on pH - without any applied potentials. You can get an estimation when looking at Pourbaix diagrams (pH-potential equilibrium diagrams) for your metal in question.

Thank you for the immediate response.

I still doubt, how would the current flow in such a system when it theoretically means OCV has zero current?

Dear Gouse

I agreed with Dr. Shanmugam ss. Your electrolyte solution at is highly acidic which induces the hydrogen evolution on a metal surface while  the metal undergoing oxidation. the metal ions at different oxidation state may give color to your solution. Apart from that OCV is the energy difference between two materials ( in your case metals) in terms of voltage. At OCV both the reaction i.e Oxidation and reduction are at equilibrium hence the net current is zero, it does not mean that there is no flow of current at OCV. the current at OCV you may also call Exchange current density (exactly exchange current density is the one where forward and backward reaction are at equilibrium in an electrochemical system). However the another chance that, If two electrode you have been using in your cell may undergo Oxidation and reduction reaction spontaneously which may give the current flow in the cell (similar to the battery while discharging).

1. If the circuit is in fact open, you may have metal dissolution in the acidic solution.

2. If you connect anode with cathode you may have internal electrolysis (think to e.m.f.,  not ocp).

3. If you are measuring the voltage as ocp (with a high impedance voltmeter) the current is always zero.

4. if you are measuring current (with a low resistance meter) and the value is zero, a zero current means equilibrium or/and no net reaction (the rate of the direct reaction is the same as the rate of the reverse reaction),

Each one is a different situation.