Increasing Iridium Oxide Activity for the Oxygen Evolution Reaction with Hafnium Modification

Fang Zhao; Bo Wen; Wenhan Niu; Zhu Chen; Chao Yan; Annabella Selloni; Christopher G Tully; Xiaofang Yang; Bruce E Koel

doi:10.1021/jacs.1c03473

Increasing Iridium Oxide Activity for the Oxygen Evolution Reaction with Hafnium Modification

J Am Chem Soc. 2021 Sep 29;143(38):15616-15623. doi: 10.1021/jacs.1c03473. Epub 2021 Sep 1.

Authors

Fang Zhao¹, Bo Wen², Wenhan Niu³, Zhu Chen³, Chao Yan⁴, Annabella Selloni², Christopher G Tully¹, Xiaofang Yang³, Bruce E Koel³

Affiliations

¹ Department of Physics, Princeton University, New Jersey, 08544, United States.
² Department of Chemistry, Princeton University, New Jersey, 08544, United States.
³ Department of Chemical and Biological Engineering, Princeton University, New Jersey, 08540, United States.
⁴ Department of Mechanical and Aerospace Engineering, Princeton University, New Jersey, 08540, United States.

PMID: 34469132
DOI: 10.1021/jacs.1c03473

Abstract

Synthesis and implementation of highly active, stable, and affordable electrocatalysts for the oxygen evolution reaction (OER) is a major challenge in developing energy efficient and economically viable energy conversion devices such as electrolyzers, rechargeable metal-air batteries, and regenerative fuel cells. The current benchmark electrocatalyst for OER is based on iridium oxide (IrO_x) due to its superior performance and excellent stability. However, large scale applications using IrO_x are impractical due to its low abundance and high cost. Herein, we report a highly active hafnium-modified iridium oxide (IrHf_xO_y) electrocatalyst for OER. The IrHf_xO_y electrocatalyst demonstrated ten times higher activity in alkaline conditions (pH = 11) and four times higher activity in acid conditions (pH = 1) than a IrO_x electrocatalyst. The highest intrinsic mass activity of the IrHf_xO_y catalyst in acid conditions was calculated as 6950 A g_IrOx^-1 at an overpotential (η) of 0.3 V. Combined studies utilizing operando surface enhanced Raman spectroscopy (SERS) and DFT calculations revealed that the active sites for OER are the Ir-O species for both IrO_x and IrHf_xO_y catalysts. The presence of Hf sites leads to more negative charge states on nearby O sites, shortening of the bond lengths of Ir-O, and lowers free energies for OER intermediates that accelerate the OER process.