Visualization of Oxygen Bubbles on a Flat Ionomer-Coated Platinum Electrode

Abstract

To improve the performance of polymer electrode membrane electrolyzers, it is necessary to grasp oxygen transport from the reaction site. This paper presents a visualization study which examines the effect of ionomers on the behavior of oxygen bubbles generated from the catalyst covered with ionomers. For the sake of visualization, a flat electrode was fabricated on a glass plate as shown Fig.1 (a). The reaction area was plated with platinum and covered entirely with ionomer using a spin coater.As shown Fig.1 (b), oxygen bubbles generated on ionomer surface were successfully captured with a high-speed camera. As shown Fig.1 (c), (d) the post visualization by electron microscopy with EDX showed that there were no significant cracks and damages on the ionomers. In other words, oxygen bubbles are generated on the ionomer surface without an apparent three-phase boundary (i.e., catalyst-ionomer-water). This suggests oxygen generated on the Pt surface was transported through the ionomer layer. The three-phase boundary may not be mandatory for the catalyst layer. The results presented in this research can provide better understanding of oxygen transport properties inside catalyst layer, thereby contributing to the future optimization of the structural design of catalyst layers. Acknowledgement This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).Fig.1 (a) Flat electrode on a glass plate, (b) Figure of the oxygen bubbles when electrolyzing, Element mapping of (c) Platinum and (d) Fluorine Figure 1