Stabilization of an iridium oxygen evolution catalyst by titanium oxides

Abstract

The anodic oxygen evolution reaction (OER) has significant importance in many electrochemical technologies. In proton exchange membrane water electrolyzers it plays a pivotal role for electrochemical energy conversion, yet sluggish kinetics and the corrosive environment during operation still compel significant advances in electrode materials to enable a widespread application. Up-to-date Iridium is known as the best catalyst material for the OER in acidic media due to its relatively high activity and long-term stability. However, scarcity of iridium drives the development of strategies for its efficient utilization. One promising way would be the formation of mixtures in which the noble catalyst element is dispersed in the non-noble matrix of more stable metals or metal oxides. A promising valve metal oxide is TiOx, yet the degree to which performance can be optimized by composition is still unresolved. Thus, using a scanning flow cell connected to an inductively coupled plasma mass spectrometer, we examined the activity and stability for the OER of an oxidized Ir–Ti thin film material library covering the composition range from 20–70 at.% of Ir. We find that regardless of the composition the rate of Ir dissolution is observed to be lower than that of thermally prepared IrO2. Moreover, mixtures containing at least 50 at.% of Ir exhibit reactivity comparable to IrO2. Their superior performance is discussed with complementary information obtained from atomic scale and electronic structure analysis using atom probe tomography and x-ray photoelectron spectroscopy. Overall, our data shows that Ir–Ti mixtures can be promising OER catalysts with both high activity and high stability.

The low overpotential regime of acidic water oxidation part II: trends in metal and oxygen stability numbers

“…The stability we measure for s-400 °C IrO 2 (crystalline Ir 18 O 2 sputter-deposited at 400 °C) is lower than some previously reported values (∼7 × 10 4 in our case compared to 10 5 –10 6 ). 38 The difference might be due to the stability number being lower at the low current densities probed by chip EC-MS or due to imperfect electrolyte exchange in the cell when the electrolyte was sampled, which could cause some of the metal dissolution from the ramp-up period to remain in the cell and cross-contaminate the steady-state electrolyte samples. Ruthenium-based samples lie well below the y = x line, meaning that they lose ruthenium atoms to dissolution much faster than they incorporate lattice oxygen into the O 2 evolved.…”

Essentials of High Performance Water Electrolyzers – From Catalyst Layer Materials to Electrode Engineering

“…[15] TiO 2 is specifically chosen as a support given its chemically stability against dissolution under anodic working conditions in PEMWEs. [20] Outstanding performances of PEMWEs using IrO 2 -TiO 2 commercial catalysts and a Nafion 212 membrane (51 µm thick) were reported by Gasteiger et al, [15,16] showing current density of 6 A cm −2 at a cell voltage of 1.92 V. However, no gas cross-over evaluation was performed in that study. Nevertheless, by thoroughly analyzing cell performance using IrO 2 -TiO 2 commercial catalyst at various loadings (0.2-5.4 mgIr cm −2 ), Gasteiger et al [15] demonstrated that the performance of the studied cells could not meet the requirement for de-carbonization of the entire transport sector until 2100.…”

Noble Metal‐Based Multimetallic Nanoparticles for Electrocatalytic Applications

“…This system has been further improved by various metal-support combinations with mechanistic studies, [339] morphology controls, [340] surface treatments, [341,342] and selection of various oxides. [343][344][345] In addition to the stabilization effect on active metal nanoparticles, there have been many reports on the promotive effects of metal oxide supports in the increased reaction kinetics, such as in methanol oxidation reaction (MOR). [346] Various multimetallic catalysts showed enhanced performance in combination with different oxide supports, which has been explained by two main reasons.…”

“…This system has been further improved by various metal‐support combinations with mechanistic studies, [ 339 ] morphology controls, [ 340 ] surface treatments, [ 341 , 342 ] and selection of various oxides. [ 343 , 344 , 345 ]…”