Oxygen Evolution Reaction Activity and Stability Benchmarks for Supported and Unsupported IrO_x Electrocatalysts

Abstract

Advanced materials are needed to meet the requirements of devices designed for harvesting and storing renewable electricity. In particular, polymer electrolyte membrane water electrolyzers (PEMWEs) could benefit from a reduction in the size of the iridium oxide (IrOx) particles used to electrocatalyze the sluggish oxygen evolution reaction (OER). To verify the validity of this approach, we built a library of 18 supported and unsupported IrOx catalysts and established their stability number (S-number) values using inductively-coupled plasma mass spectrometry and electrochemistry. Our results provide quantitative evidence that (i) supported IrOx nanocatalysts are more active towards the OER but less stable than unsupported micrometer-sized catalysts, e.g. commercial IrO2 or porous IrOx microparticles; (ii) tantalum-doped tin oxides (TaTO) used as supports for IrOx nanoparticles are more stable than antimony-doped tin oxides (ATO) and carbon black (Vulcan XC72); (iii) thermal annealing under air atmosphere yields depreciated OER activity but enhanced stability; (iv) the beneficial effect of thermal annealing holds both for microand nano-IrOx particles, and leads to one order of magnitude lower Ir atom dissolution rate with respect to non-annealed catalysts; (v) the best compromise between OER activity and stability was obtained for unsupported porous IrOx microparticles after thermal annealing under air at 450°C. These insights provide guidance on which material classes and strategies are the most likely to increase sustainably the OER efficiency while contributing to diminish the cost of PEMWE devices.

Advances in Oxygen Evolution Electrocatalysts for Proton Exchange Membrane Water Electrolyzers

“…Studies have shown that the dissolution can be alleviated by thermal annealing, despite the sacrifice of activity. [ 334 ] It is emphasized that electronic structure regulations and mechanism modulations help regulation of oxidation states [ 335 ] to avoid severe dissolution, which have been mentioned above. Moreover, the optimization of CL layer structure plays an important role in promoting mass transfer and maintaining stability.…”

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

“…However, due to the lack of conductivity, still relatively high iridium loadings are needed. 19 As potential alternative supports, tin oxide 20 and its doped analogues, such as antimony-doped tin oxide (ATO), 21 − 23 indium-doped tin oxide (ITO), 24 fluorine-doped tin oxide (FTO), 25 and tantalum-doped tin oxide (TaTO) 26 are often proposed; however, their use is still limited to the laboratory scale due to their stability constraints. 20 , 25 One of the potential supports is also doped titanium oxides.…”

ALD‐Coated Mesoporous Iridium‐Titanium Mixed Oxides: Maximizing Iridium Utilization for an Outstanding OER Performance

“…[22] The interested reader is referred to a comprehensive review by Maillard and co-workers. [23] With the increasing production of renewable energy and concomitant depletion of fossil resources, the demand for efficient water splitting electrocatalysts continues to grow. Iridium (Ir) and iridium oxides (IrO x ) are currently the most promising candidates for an efficient oxygen evolution reaction (OER) in acidic medium, which remains the bottleneck in water electrolysis.…”