Sacrificial Cu Layer Mediated the Formation of an Active and Stable Supported Iridium Oxygen Evolution Reaction Electrocatalyst.

Anja Lončar,Marjan Bele,Martin Šala,Primož Jovanovič,Nejc Hodnik,Daniel Escalera-López,Francisco Ruiz-Zepeda,Serhiy Cherevko,Armin Hrnjić

doi:10.1021/acscatal.1c02968

Abstract

The production of hydrogen via a proton-exchange membrane water electrolyzer (PEM-WE) is directly dependent on the rational design of electrocatalysts for the anodic oxygen evolution reaction (OER), which is the bottleneck of the process. Here, we present a smart design strategy for enhancing Ir utilization and stabilization. We showcase it on a catalyst, where Ir nanoparticles are efficiently anchored on a conductive support titanium oxynitride (TiONx) dispersed over carbon-based Ketjen Black and covered by a thin layer of copper (Ir/CuTiONx/C), which gets removed in the preconditioning step. Electrochemical OER activity, stability, and structural changes were compared to the Ir-based catalyst, where Ir nanoparticles without Cu are deposited on the same support (Ir/TiONx/C). To study the effect of the sacrificial less-noble metal layer on the catalytic performance of the synthesized material, characterization methods, namely X-ray powder diffraction, X-ray photoemission spectroscopy, and identical location transmission electron microscopy were employed and complemented with scanning flow cell coupled to an inductively coupled plasma mass spectrometer, which allowed studying the online dissolution during the catalytic reaction. Utilization of these advanced methods revealed that the sacrificial Cu layer positively affects both Ir OER mass activity and its durability, which was assessed via S-number, a recently reported stability metric. Improved activity of Cu analogue was ascribed to the higher surface area of smaller Ir nanoparticles, which are better stabilized through a strong metal–support interaction (SMSI) effect.

Highlights

The transition to a clean and sustainable society is predicted to occur by the use of green hydrogen as an energy vector that can replace fossil fuels.[1]
Two new peaks at 40.7° (111) and 47.3° (200) are seen in the spectra of Ir/TiONx/C and Ir/ CuTiONx/C after the final step of the synthesis, which are attributed to the crystalline cubic iridium (⧫, PDF 04-0078342)
We have presented the synthesis and characterization of two analogues of the iridium electrocatalyst supported on titanium oxynitride, dispersed over the highsurface-area Ketjen Black

Summary

■ INTRODUCTION

The transition to a clean and sustainable society is predicted to occur by the use of green hydrogen as an energy vector that can replace fossil fuels.[1]. As iridium is currently not replaceable, its utilization needs to be optimized It can be achieved by increasing its surface area by decreasing the size, adjusting the morphology or crystallinity of the nanoparticles,[10−12] by the formation of more active electrochemical amorphous oxide,[13] development of a core−shell structure,[14] or mixing iridium with different metals, such as Ru,[15] Ni, Co,[17] and Cu18 to tune its electrocatalytic performance. Both samples, Ir/TiONx/C and Ir/CuTiONx/ C, were prepared following the same protocol. To observe the changes in the nanoparticles after the electrochemical treatment, an identical location transmission electron microscopy (IL-TEM) technique was used The activity was measured afterward with a linear scan of potential with 20 mV/ s from 1.2 V to the cut-off at 5 mA cm−2

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES