CuCl/HCl Electrolysis for Cu-Cl Thermochemical Cycle
Open Access
- Author:
- Schatz, Richard S
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- December 21, 2012
- Committee Members:
- Serguei Lvov, Thesis Advisor/Co-Advisor
- Keywords:
- Hydrogen Production
CuCl/HCl Electrolysis
Cu-Cl Thermochemical Cycle
Green energy - Abstract:
- The Cu–Cl thermochemical cycle is among the most attractive technologies proposed for hydrogen production due to moderate temperature requirements and high efficiency. In this study, the key step of the cycle, H2 gas evolution via oxidation of CuCl(s) dissolved in high concentrated HCl(aq), was experimentally investigated. The research covered in this study was carried out in three phases. In the first phase, the electrolysis parameters and system performance were studied by linear sweep voltammetry and electrochemical impedance spectroscopy at ambient temperature. A thermodynamic model previously developed for speciation of the CuCl–CuCl2–HCl aqueous solutions was used to speculate on the effects of reagent concentration, flow rate, and temperature on electrolysis kinetics. The main conclusions from this phase were a close correspondence of the hydrogen production rate to Faraday’s law of electrolysis indicated, a current efficiency of about 0.98, while the voltage efficiency was estimated at 0.80 at 0.5 V and 0.1 A•cm-2. A current density of 0.08 A•cm-2 was observed at 0.7 V, using 0.26 mol CuCl(s) in 3 mol•L-1 HCl at a flow rate of approximately 30 mL•min-1 for both solutions. In the second phase, the electrolyzer was upgraded to address the inefficiencies and limitations identified in the previous system setup. After a control test, the electrolyzer was ran using a new type of double layer Nafion 117 membrane to test MEA durability. The enhanced MEA durability allowed the system to operate at 80 ºC for an extended period of time with continuous anolyte cycling and regeneration. The system was observed over a period of 100 hours to test the effects of long term operation on the electrolyzer. Linear polarization and electrochemical impedance spectroscopy were used to monitor the electrolyzer performance over time and hydrogen production was monitored to evaluate the current efficiency. A current density of 0.16 A•cm-2 was observed at 0.7 V, using 2 mol CuCl(s) in 7 mol•L-1 HCl(aq) at a flow rate of approximately 59 mL•min-1 for both solutions. Current efficiency remained the same as previously observed, about 0.98. In the final phase, the electrolyzer was completely redesigned to address the inefficiencies and limitations identified in the previous system setup and provide optimum electrolyzer performance and measurement accuracy. A current density of 0.50 A•cm-2 was observed at 0.7 V, using 2 mol CuCl in 6 mol•L-1 HCl(aq) at a flow rate of approximately 30 mL•min-1 for both solutions. The hydrogen production efficiency was found to be 0.91-0.99 without any decline during the test.