(Invited) From Material Discovery Towards a Prototype Hydrogen Generator

Abstract

This contribution illustrates the approach that has been taken to develop a pre-commercial prototype of a water electrolyzer. The aim has been to develop and integrate novel nanostructured materials for both electrodes and membranes, demonstrating their upscaling potential by integrating them together in a water electrolysis cell with an active surface are of 50 cm² in order to proof their potential for further advancing the state of the art of green hydrogen generation.Based on industrial experience with medium flow hydrogen generators, the boundary conditions for the new electrode and membrane components were set, safeguarding their integration potential in a scalable stack. A nano-porous intrinsically conductive membrane material has been developed, that allows to drastically reduce the thickness of the separator, reducing ohmic losses without compromising gas separation quality during operation at elevated pressures (up to 20 barg). This was combined with nanostructured electrodes of 4-10 μm thickness on both sides of the membrane. Given the vast range of dimensional scales, from 10-8 to 10-1 m, special attention was needed for the interconnections of the materials to establish the required electronic and ionic coupling together with adequate mechanical robustness. Two phase fluid flow modelling was done do have an optimal reactant distribution and gas evacuation from the electrode surfaces. Aspects like contact resistance, elasticity, stiffness, and overall electric field distribution inside the cell were considered. To characterize the cell in operation, a dedicated balance of plant has been built (Fig.1). The installation is automated and takes care of the electrolyte solution conditions and of the process window settings in terms of applied current, electrolyte flow and operational temperature at a pre-set pressure. The resulting cell potential, the gas purity of both oxygen and hydrogen streams and the differential pressure between anolyte and catholyte chambers are continuously monitored. The upscaled cell demonstrates a high hydrogen generation efficiency of 85% (HHV) that outperforms currently installed alkaline systems in terms of productivity and gas purity when operated at an elevated pressure 20 bar. The cell robustness, documented over 800 hours, reveals further areas of improvement for both the internal construction of the stack and the control logic of the balance of plant. Figure 1