Measuring and quantifying shunt currents in an alkaline water electrolyser shortstack

Abstract

Hydrogen is used in a variety of industrial applications and can function as a green energy carrier, if produced sus-tainably. Alkaline water electrolysis holds great promise as a production method for green hydrogen, potentially playing an important role in the energy transition. The performance of this technology depends significantly on its electrical efficiency. In some industrial-scale green hydrogen plants, multiple electrolysis cells are coupled together in series or in parallel to form a stack. These electrolyser stacks are being fed with a liquid electrolyte, often a KOH solution, which acts as a good conductor for ions to move between electrodes. The channels through which the electrolyte and gas products are transported in and out of the stack are usually connected to each other via manifolds. Electrolyzer stacks frequently encounter a problem known as shunt current, which is alternatively described as leakage, bypass, or parasitic current in various studies through these channels and manifolds. Math-ematically describing the magnitude and nature of these shunt currents has been the topic of a variety of studies. Being able to adequately measure and quantify shunt currents in an actual stack remains a challenge. This study aims to measure and quantify shunt currents in a novel electrolyser stack design by the employment of hydrogen reference electrodes, copper or silver pseudoreference electrodes, and a magnetic current clamp. Numerous ex-perimental findings have been coupled with mathematical models, imaging and theoretical expectations offering detailed insights in the behaviour of shunt currents with varying external factors. The variable parameters in this shunt current research are the applied current density to the stack and the applied liquid flow rate, by an external pump. The performance of hydrogen reference electrodes, copper and silver wires separately, to measure potential dif-ferences in an electric field generated in the highly alkaline environment of a 6M KOH solution was validated. It was found that the hydrogen reference electrodes functioned accurately and stable, giving conductivity results of the electrolyte 7.5 % above measurements performed with a conductivity probe. The copper wires functioned less predictable and stable, giving values 16 % above the validated value, with a larger spread and less reproducibility. The silver wires showed great potential, providing a value of 3 % above the validated value, but showed less stability in measuring constant potential differences. The plain copper and silver wires only functioned for short term measurements, where a potential difference between a baseline potential was the only predictable outcome. Both lacking a stable redox potential, they were found not suitable for accurately measuring potential differences inside the stack. The hydrogen reference electrodes proved to be useful in quantifying average manifold shunt currents, however leaving uncertainties as to total shunt currents in the experimental set-up used in this research. The magnetic current clamp was used to measure the current running through the external wiring between cells, from which the shunt current could be inferred. These measurements showed much potential in quantifying total shunt currents, but showed a large standard deviation between measurements due to the instantaneous nature of the measure-ments, alongside unpredictable electrode connections interfering with the outcomes...