Reference Electrode Development in Polymer Electrolyte Membrane (PEM) Electrolyzer Assembly for Novel Investigation of Electrodes
Polymer electrolyte membrane electrolyzers (PEMEs) are the key to integrating renewable energy generation with energy storage to reduce greenhouse gas emissions that contribute to global climate change. The commercialization of large PEME systems, however, requires improvements to electrode design, performance, and reduction of material costs. In particular, reducing the precious metal loading at the oxygen producing electrode (anode) is critical to making PEME commercially competitive. Measuring the electrode potentials separately is imperative to understanding and improving cell performance. A reliable reference electrode (RE) can provide much more precise information about the anode performance. A RE was developed for PEME application. The efficacy of the RE was confirmed by two parametric studies. The first parametric study served to demonstrate that the combined individual electrode potentials measured with the RE were exactly consistent with the overall potential difference of the cell. A second parametric study confirmed sufficient hydrogen polarization of the RE for operating conditions at low current density, low temperature, and low water feed rates. Application of the RE was successfully demonstrated through investigation of the oxygen evolution and hydrogen evolution reaction mechanisms occurring at the anode and cathode, respectively. Tafel slopes were calculated and the rate determining steps were determined that support specific proposed reaction mechanisms reported in literature. This investigation revealed important characteristics of each electrode. In particular, it was shown that the cathode overvoltage should not be assumed negligible for the ohmic controlled operating region and more precise information can be observed for the anode performance. These results demonstrate the necessity of the in-situ RE to improving PEME performance.