A mathematical model for optimum design and synthesis of a hybrid electrolyser-fuel cell system: Production of hydrogen and freshwater from seawater

Abstract

Fossil fuels have earned a reputation as unsustainable sources of energy, due to the release of carbon emissions that are attributable to global warming. To overcome the extensive release of carbon emissions into the environment, different approaches are being explored to produce energy, by replacing non-renewable fuels with renewable energy. Additionally, many countries across the world are emerging as water-scarce countries, due to the vulnerability of freshwater supply. This work, therefore, focuses on the design and synthesis of a hybrid electrolyser-fuel cell system to generate hydrogen and freshwater from seawater. The proposed system is designed to be integrated with a background process that requires both power and water. It has the potential to reduce the burden on freshwater sources and carbon footprint of background processes, as well as produce power. A one-dimensional, mathematical model is developed for a continuous hybrid seawater electrolyser-fuel cell system operated at steady state. The model determines the optimal operating conditions in terms of temperature, current density, electrode thickness and humidity, as well as the performance of the system through the activation overpotential, diffusion overpotential, ohmic overpotential and the open-circuit voltage. GAMS/BARON is used to optimise the hybrid system. Furthermore, a techno-economic evaluation is conducted to determine the viability of the system. Results indicate that an overall power conversion efficiency of 41.2 %, and a freshwater recovery rate of 48.2 % is achieved.