Microwave‐Assisted Synthesis of Stable and Highly Active Ir Oxohydroxides for Electrochemical Oxidation of Water

Abstract

Water splitting for hydrogen production in acidic media has been limited by the poor stability of the anodic electrocatalyst devoted to the oxygen evolution reaction (OER). To help circumvent this problem we have synthesized a class of novel Ir oxohydroxides by rapid microwave-asisted hydrothermal synthesis, which bridges the gap between electrodeposited amorphous IrO films and crystalline IrO electrocatalysts prepared by calcination routes. For electrode loadings two orders of magnitude below current standards, the synthesized compounds present an unrivalled combination of high activity and stability under commercially relevant OER conditions in comparison to reported benchmarks, without need for pretreatment. The best compound achieved a lifetime 33 times longer than the best commercial Ir benchmark. Thus, the reported efficient synthesis of an Ir oxohydroxide phase with superior intrinsic OER performance constitutes a major step towards the targeted design of cost-efficient Ir based OER electrocatalysts for acidic media.

Reactive Electrophilic OI− Species Evidenced in High‐Performance Iridium Oxohydroxide Water Oxidation Electrocatalysts

“…The base/Ir ratio in the initial precursor solution was identified as a key parameter to tune the structural properties and OER performance. The systematic variation of this parameter yielded a family of iridium oxohydroxides and provided an opportunity to uncover correlations between the structural features and OER performance to establish functional links . A moderate excess of base led to highly nanostructured, nanocrystalline, Ir III ‐rich oxohydroxides with outstanding OER performances.…”

“…The samples prepared with KOH/Ir=4:1 and 5:1 exhibited the best OER performances, and an optimal synthesis yield was obtained for KOH/Ir=5:1 . In contrast, at KOH/Ir≥7:1, the performance decreased rapidly.…”

“…In our previous report on the MW‐supported hydrothermal synthesis of iridium oxohydroxides, we mentioned the great difficulty of studying such compounds through electron microscopy owing to the rapid transformation of the nanocrystalline oxidic Ir phase into metallic iridium . As a strategy to avoid radiation damage, we chose to encapsulate the MWproduced iridium oxohydroxide between graphene sheets .…”

“…To test this hypothesis and study the functional relationship between the electronic structure of iridium(III/IV) oxohydroxides and their OER performances, we prepared a family of iridium oxohydroxides through an innovative microwave‐supported (MW‐supported) hydrothermal synthesis . The base/Ir ratio in the initial precursor solution was identified as a key parameter to tune the structural properties and OER performance.…”

High‐Performance Supported Iridium Oxohydroxide Water Oxidation Electrocatalysts

“…[70] Experimental Section ATOsynthesis Antimony-doped tin oxide (ATO) was obtainedf rom SnCl 4 ·5H 2 O( Sigma-Aldrich) and SbCl 3 (Sigma-Aldrich) dissolved in a9 5:5m olar ratio in a0 .5 %H Cl/H 2 Os olution.T he metal chloride solution was added to H 2 O( 200 mL) under constant stirring at as peed of 5gmin À1 using an automated laboratory reactor system (Mettler-Toledo, Labmax). The resulting Ir III/IV oxohydroxide compounds bypasst he conundrum of havingt os acrifice activity for stability by producing crystalline IrO 2 phases.T oo btain am ore thorough understanding of the Ir oxohydroxidep hase without the influence of support-effects, follow-up work will focus on unsupported amorphous Ir oxohydroxides to gain deeper insight into OER-relevant speciesh ostedb yt he Ir III/IV oxohydroxide structure.…”