Development of Novel Ternary Non-Pt Alloy Catalyst for Oxygen Evolution Reaction

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) have attracted increasing interest as promising powertrain for zero-emission vehicles because of their high energy density, high conversion efficiency, and zero greenhouse gases emission [1,2]. However, there are still two challenges such as cost and durability for wide commercialization of fuel cell electric vehicles (FCEVs) because startup/shutdown (SU/SD) and cell reversal (CR) phenomena occur approximately 5,000 and 200 times, respectively, during the lifetime operation of FCEV [3]. The cell reversal voltage in the anode is caused by hydrogen fuel starvation, which comes from the various transient conditions that lead to the fatal cell failure in a few minutes [4]. To mitigate the detrimental degradation of the electrode, two primary approaches have been investigated. The first strategy is a system level control which interferes with the operation of the fuel cell stack and challenges the reliability of the operations. The second one is materials based solutions including a oxygen evolution reaction (OER) favorable catalysts, oxidation resistant supports, functional additives and higher binder loading within the catalyst layer. Recently, application of OER catalyst has been reported as an effective solution for reversal tolerant anode (RTA) [4,5]. In the previous study, IrRu-based OER catalysts[4] by simple impregnation method showed a superior activity towards OER in the acidic condition, which has at least an over-potential of 75 mV lower than the commercial IrO2 at 10mA/cm2. In the present study, the ternary alloy catalyst is investigated by an introduction of Y element to the IrRu composition to alter the activity and durability of the catalyst because the Y alloy with Pt is reported to enhance the activity and stability towards ORR in the previous papers [6,7]. In addition, there is no report for the IrRuY alloy as OER catalyst in acid media until now. These nanoparticles were synthesized by electron beam method, which is not only eco-friendly but also a mass production capability in a short time. To secure the metallic state of all component, hydrogen reduction process at higher temperature is conducted. Through the XPS analysis, all of the elements in the IrRuY-based catalysts were confirmed as a metallic state. The XRD pattern for IrRuY nano-particles revealed the presence of well-defined diffraction peaks at 43.85°, which implies that nanoparticles in the IrRuY catalyst have the hexagonal close-packed structure of Ru. TEM images showed a trend that the average size of metal nanoparticles is decreased with increasing the Y content in the catalysts compared to supported IrRu4 nanoparticles. From the half-cell test, heat-treated IrRu4Y3 among the IrRuY-based OER catalysts displayed the best activity at 10mA/cm2, which is an over-potential of 90 mV lower than the IrRu4/C. It would be the most active OER catalysts for the RTA of the automotive PEMFC.