Design, analysis and experimental investigation of Cu-Cl based integrated systems

Abstract

Burning fossil fuels for power generation results in emissions of greenhouse gases such as carbon dioxide (CO2) and air pollutants such as nitrogen oxides (NOx) and sulfur oxides (SOx), which are harmful to living creatures and the natural environment. Due to the negative effects of using fossil fuels, significant research is being carried out in the area of alternative energy carriers such as hydrogen, which can replace fossil fuels in the future. Hydrogen can be produced in a relatively environmentally friendly manner by using the copper-chlorine (Cu-Cl) thermochemical water splitting cycle (TWSC) due to its minimal reliance on fossil fuels, relatively lower operating temperature requirement and better overall efficiency as compared to other TWSCs. The electrolysis step of the Cu-Cl cycle is one of the most important steps, since it produces the hydrogen gas. The dependence of the Cu-Cl cycle on the electricity grid to run the electrolysis step impacts the overall environmental sustainability of the process. The aim of this study is to perform experimental investigations of the hybrid photocatalytic hydrogen production reactor for the Cu-Cl cycle. The electrochemical, energy, exergy and exergoeconomic analyses of the hybrid reactors are carried out to observe the effects of variation in different operating parameters on the performance of the system. The comparative energy and exergy analyses of two solar-based integrated systems are also conducted to show how the performance of integrated systems can be improved by recovering reflected solar light intensity in the photocatalytic hydrogen production reactor. The results obtained from the photo-electrochemical experimental study show that an increase in the voltage, solar light intensity, concentration of CuCl and concentration of ZnS increases the hydrogen production rate. The experimental results also show that the amount of voltage generated by inducing solar light intensity on titanium dioxide increases with an increase in the concentration of the titanium dioxide. The results based on electrochemical modeling of the hybrid reactor show that an increase in current density results in a higher voltage requirement by the hybrid photocatalytic reactor. The experimental hydrogen production rate and cost of hydrogen production is observed to increase from 1.28 to 1.47 L/s and 3.28 to 3.36 C$/kg, respectively, with a rise in reactor temperature. Energy and exergy analyses of the solar-based integrated systems show that the rates of hydrogen production by systems 1 and 2 increase from 126.9 to 289.4 L/s and 154.1 to 343.9 L/s, respectively, with a rise in solar light intensity. The exergy efficiencies of systems 1 and 2 increase from 47.98 to 50.82% and 56.87 to 59.64%, respectively, with a rise in ambient temperature.