Surfactant Free-Ir/IrOX Catalysts with Improved Activity and Stability for Polymer Electrolyte Membrane Water Electrolyzer
Authors: Lee Seung Woo , Baik Chaekyung , Pak Chanho 
Published: May 2020

As renewable energy technologies have advanced, their power generation capacity has improved commensurately. However, since they often experience intermittent power generation problems, it has been suggested that a solution, which is to use water electrolysis (WE) technology to convert electric power into hydrogen energy. One option to accomplish this is polymer electrolyte membrane water electrolysis (PEMWE). This technique is attractive because it produces high purity H2, has a rapid response rate, and supports high current density operation, among other features [1]. However, before PEMWE can be properly commercialized, challenges of efficiency and stability must be addressed. PEMWE involves both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). However, the kinetics of the OER is much more sluggish than those of the HER, which decreases the overall WE efficiency. Furthermore, as the OER takes place in harsh environments (e.g., high voltage and low pH), the stability of the materials used in PEMWE is of concern. In an effort to overcome this huddle, researchers have focused on the development of OER catalysts [2-4].

Compared to the previous study [5, 6], the Ir/IrOX catalyst is prepared by using formic acid and polyol as the reducing agent and solvent, respectively, absence of any surfactant assistance in this study. It is worth in terms that the mass production of catalysts could be possible through this process. In half cell test (Fig. 1(a)), although the Tafel slopes of Ir/IrOX and state-of-art IrO2 (TKK, Tanaka Kikinzoku Kogyo) for the OER is similar, the catalytic activity of the former is more excellent until 1.45 VRHE (IR-free). To reveal an enhanced catalyst activity and stability towards OER, we fabricated MEAs using Ir/IrOX catalysts and TKK-IrO2 as anode catalysts, and commercial Pt/C at a cathode catalyst, respectively. As shown in Fig. 1(b), the performance of single-cell was compared at 2 A cm-2
geo. under the 353 K condition and is of Ir/IrOX (2.04 V), and TKK-IrO2 (2.32 V), respectively. This result indicates that the energy efficiency of the MEA using the Ir/IrOX catalyst is higher 13.72 % than that of TKK-IrO2. The obtained results are expected to decrease the amount of precious metals required to develop a cost-effective water electrolysis system for renewable hydrogen production.

This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20183010032380), and GIST.

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Figure 1