Nanostructured Ir-supported on Ti4O7 as a cost-effective anode for proton exchange membrane (PEM) electrolyzers

Abstract

PEM water electrolysis has recently emerged as one of the most promising technologies for large H₂ production from a temporal surplus of renewable electricity; yet it is expensive, partly due to the use of large amounts of Ir present in the anode. Here we report the development and characterization of a cost-effective catalyst, which consists of metallic Ir nanoparticles supported on commercial Ti₄O₇. The catalyst is synthesized by reducing IrCl₃ with NaBH₄ in a suspension containing Ti₄O₇, cetyltrimethylammonium bromide (CTAB) and anhydrous ethanol. No thermal treatment was applied afterwards in order to preserve the high conductivity of Ti₄O₇ and the metallic properties of Ir. Electron microscopy images show an uniform distribution of mostly single Ir particles covering the electro-ceramic support, although some agglomerates are still present. X-ray diffraction (XRD) analysis reveals a cubic face centered structure of Ir nanoparticles with a crystallite size of ca. 1.8 nm. According to X-ray photoelectron spectroscopy (XPS), the ratio of metallic Ir and Ir-oxide, identified as Ir³⁺, is 3 : 1 after the removal of surface contamination. Other surface properties such as primary particle size distribution and surface potential were determined by atomic force microscopy (AFM). Cyclic and linear voltammetric measurements were conducted to study the electrochemical surface and kinetics of Ir-black and Ir/Ti₄O₇. The developed catalyst outperforms the commercial Ir-black in terms of mass activity for the oxygen evolution reaction (OER) in acid medium by a factor of four, measured at 0.25 V overpotential and room temperature. In general, the Ir/Ti₄O₇ catalyst exhibits improved kinetics and higher turnover frequency (TOF) compared to Ir-black. The developed Ir/Ti₄O₇ catalyst allows reducing the precious metal loading in the anode of a PEM electrolyzer by taking advantage of the use of an electro-ceramic support.