Electrolyser voltage reduction

Fig. 16.12 Principle and advantages of the falling film electrolyser. Advantages include improved mass and heat transfer low gas content in electrolyte low concentration difference constant hydraulic pressure low expected voltage of 2.70 V at 3 kA m-2 leading to power consumption reduction of 70 kWh per tonne of NaOH at 4kA m-2, including circulation pumps and small element depth. 

A zero-gap electrolyser is currently under trial. In pilot-scale operation, it has demonstrated a cell voltage of 3.0-3.1 V at a current density of 6 kA m-2. The results indicate that completion of zero-gap technology will bring a further reduction in unit power consumption of 100 kWh per tonne of NaOH. 

The best results are obtained with the PEM electrolyser current density of 1 200 A/m2 under cell voltage of 1 V corresponding to a hydrogen production of 500 NL.fr1.nr2. The results from both electrolysers show sulphur deposition at the cathode. This chemical reduction consumes electrons at the expense of hydrogen production causing sulphur to poison the catalyst and modify the membrane conductivity. 

The further improvements of the described above solution of the high-pressure alkaline electrolyser mainly concern the optimisation of the composition and preparation technology of the active electrodes. So, the application of the electrochemically-deposited materials for making the active electrodes allows to significantly reduce the voltage drop (to 0.6-1.5 V, as compared to 1.7-2.2 V which is specific value for the conventional low-temperature electrolysers). In turn, the increase of the output pressure to 200 bar makes it possible to increase the operation temperature to 150 °C that results in the reduction of the overpotential. It increases the efficiency reducing the power consumption for the production of 1 m3 H2 and 0.5 m3 02 to 4.1 kW h. 

---