Development and analysis of a high temperature electrolyser for the Cu-Cl cycle for hydrogen production
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A number of thermochemical cycles have been investigated to produce hydrogen from water. However, most of these cycles operate at over 800°C. The relatively lower temperature (550°C) requirement and use of inexpensive chemicals make the copper-chlorine (Cu-Cl) thermochemical cycle a promising process for hydrogen production. Building a large scale hydrogen production facility based on this cycle presents some challenges that need to be resolved. This thesis addresses the challenges of the Cu-Cl cycle by incorporating high temperature electrolysis to propose and assess four novel configurations of the Cu-Cl cycle. Four novel Cu-Cl cycles using high temperature electrolytic step for hydrogen production are proposed and thermodynamically assessed. In addition, a novel hybrid Cu-Cl cycle for the co-production of hydrogen and copper using copper waste is proposed and assessed thermodynamically. An experimental investigation is made to establish the feasibility of the high temperature electrolytic step. The results suggest that using high temperature electrolysis in the Cu-Cl cycle may be beneficial as it provides a higher energy efficiency than some similar cycles reported in the literature. A detailed electrochemical model is developed to study the J-V characteristics for the proposed electrolyser (a solid oxide electrolyser based on proton conducting electrolyte). The developed model includes all the major losses namely activation, concentration and ohmic losses. Furthermore, energy and exergy analyses are also carried out. The value of energy and exergy efficiencies of the proposed electrolyser are 41.1% and 39.0%, respectively. Simulation results show that at 1073 K, P=100.325 kPa and J=1000 A/m2, 1.6 V is required to produce 1 mole of hydrogen which is 0.3 V (approx.) less than the voltage required by the high temperature steam electrolyser (based on proton conducting electrolyte) operating at the same conditions (T=1073 K, P=101.325 kPa and J=1000 A/m2) suggesting that using the proposed electrolyser a new avenue may be open for high temperature electrolysis for hydrogen production, potentially with a low electrical energy requirement. The cost of hydrogen production from the three step Cu-Cl cycle (Scheme 4) is $4.18 per kg of hydrogen. In addition, two nuclear based integrated systems for the production of electricity, fresh water and hydrogen are proposed and assessed. System 1 is more efficient than System 2 in terms of energy and exergy efficiencies and has lower exergy destructions.