Modeling 3D hybrid battery-electrolyzer nickel electrodes

An integrated battery-electrolyzer stores renewable electricity as a battery and produces hydrogen when overcharged. This dual application requires electrode concepts that ideally enhance both battery and electrolysis operation without compromising either. One such concept is 3D structured electrodes including channels that improve ionic conductivity and material utilization as well as facilitating bubble removal during electrolysis. In this work, we first develop a 1D model of a porous sintered nickel electrode that takes the void fraction of the 3D geometry into account and allows for the determination of the current and potential distribution for both battery charging and oxygen evolution. An optimized void fraction that maximizes the reactive surface area for oxygen evolution is determined, and we discuss under what circumstances a 3D geometry is beneficial. Finally, we show how the improved ionic conductivity of 3D electrodes also results in more homogeneous battery charging, increasing charging efficiency in nickel electrodes.