[mkbh10]

I have to setup a photoelectrochemical expt to generate hydrogen gas using ZnO/TiO2 film . The lab doesn't have a gas chromatograph so I need to know whats the easy and cheap way to measure the concentration of the evolved hydrogen gas ?

[Arkcon]

Hmmm, tricky.  What other gases are likely present?  Just water vapor, or also air?  Can you just use the volume collected, and account for everything else?

[mkbh10]

Hydrogen gas will be present due to reduction at cathode and oxygen at anode. The bubles present at the cathode can give an indirect indication of hydrogen gas presence but I need to quantify the amount of gas present. 

[Arkcon]

OK, so no air.  I assume you're keeping the oxygen produced separate.  I may be wrong about that, some commercial electrolysis rigs use concentric electrodes, and the gasses end up mixing.  Shudder. You can compensate for the water vapor, that's a look-up table, and some basic high school chemistry problem.  You can scrub other gasses out using a reaction tube: for oxygen, a tube full of oxidizable compound will scrub the gas.  For that matter, a drying tube would take care of water vapor.  But sampling the gas and analyzing by GC would be simplest.