Hydrogen production from water using solar cells powered nafion membrane electrolyzers
The aims of this thesis are two folds; to construct single and multi cell proton exchange membrane electrolyzers and to evaluate the performance of these electrolyzers powered by solar panels on Iztech campus. All other parts, except the purchased membrane electrode assemblies, were designed, manufactured and assembled in our labs.In the construction of single and multiple cell proton exchange membrane electrolyzers, Nafion-117 based membrane electrode assemblies were used. Graphite bipolar plates, end plates, current collectors and gaskets were machined on institute.s computer numerical controlled lathe. In the first stage, a single cell electrolyzer with 20cm2 available electrolysis surface areas was examined with a direct current power supply by varying current density (0-500mAmp/cm2), water flow rate (0.05 to 0.5g/cm2min), and temperature (30-50oC). It was found that average cell voltage decreases from 2.18V at 30oC to 1.97V at 50oC when the current density is 500mAmp/cm2. Since cell gaskets were softened and stick to the membrane above 50oC of operating temperature, temperatures higher than 50 oC could not be tested. Five cell electrolyzer stack was constructed according to the final single cell design. It was observed that the stack could generate 388ml/min hydrogen under 500mAmp/cm2 and 10.09V of the operating condition at 41.5oC. When the stack was directly coupled with a solar array, voltage of the stack was found to vary from 7.5V to 12.5V and the current density changes from 0 to 1000mAmp/cm2 with respect to the solar radiance of the day. This results in a voltage efficiency ranging from 98.7% to 60% based on the higher heating value of hydrogen. Electrolyzer powered by solar cells can generate up to 750ml/min hydrogen and total daily production could be as high as 350L per day but weather condition greatly affects the production rate. Together with the losses inside the electrolyzer, another important energy loss is due to voltage mismatches between PV array and electrolyzer in low solar irradiance during sunrise and sunset.