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<p>Scalable synthesis of the nanoparticulate iridium-based electrocatalysts (Ir-IrO<sub>x</sub>) for the oxygen evolution reaction (OER) in acidic media is demonstrated using single phase microwave- (MW-) assisted milli-fluidic continuous flow synthesis (MF-CFS) technique. The flow reactions were initiated in the MW cavity reactor, where Ir<sup>4+</sup> was reduced by NaBH<sub>4</sub> to form Ir-IrO<sub>x</sub> nanoparticles (NPs) of particle size ranging from 2.0 to 3.5&#xa0;nm. Effects of (<i>i</i>) the Ir precursor concentration, (<i>ii</i>) the pre-mixing time interval between precursor/reducing agent mixing and injection of the mixture in the MW cavity (<i>t</i><sub>pre−mix</sub>) and (<i>iii</i>) the residence time in the MW cavity (<i>t</i><sub>r</sub>) were investigated to optimize the reaction conversion efficiency (𝜂<sub>c</sub>) and the electrochemical performance of the synthesized electrocatalysts. The value of 𝜂<sub>c</sub> was impressively increased from 52% to ~ 98% by changing the value of <i>t</i><sub>r</sub> from 2.4&#xa0;min to 4.7&#xa0;min while keeping all other parameters constant. The Ir-IrO<sub>x</sub> electrocatalysts synthesized under optimal synthesis conditions demonstrate an excellent OER mass activity of 351&#xa0;A g<sup>−1</sup> compared to that of 305&#xa0;A g<sup>−1</sup> for the commercial IrO<sub>2</sub>. During a potentiodynamic accelerated stress test (AST), the synthesized electrocatalysts show an electrochemical stability comparable to or higher than that of the commercial IrO<sub>2</sub>. The Ir-IrO<sub>x</sub> sample having the optimal OER performance exhibited an OER activity retention of 40% compared to 31% for the commercial IrO<sub>2</sub>. Longer <i>t</i><sub>r</sub> and additional MW exposure of the reaction bath was found to decrease the oxidation number of the Ir-IrO<sub>x</sub> surface efficiently, enhancing both the OER activity and durability of the synthesized Ir-IrO<sub>x</sub> sample.</p>

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Microwave assisted flow synthesis of Ir-IrOx electrocatalysts for acidic oxygen evolution reaction: synthesis conditions and electrocatalytic performance correlation

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  • 发表日期：

    2025年7月25日

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  • Inayat Ali Khan,
  • Per Morgen,
  • Saso Gyergyek,
  • Raghunandan Sharma,
  • Shuang Ma Andersen

摘要

Scalable synthesis of the nanoparticulate iridium-based electrocatalysts (Ir-IrOx) for the oxygen evolution reaction (OER) in acidic media is demonstrated using single phase microwave- (MW-) assisted milli-fluidic continuous flow synthesis (MF-CFS) technique. The flow reactions were initiated in the MW cavity reactor, where Ir4+ was reduced by NaBH4 to form Ir-IrOx nanoparticles (NPs) of particle size ranging from 2.0 to 3.5 nm. Effects of (i) the Ir precursor concentration, (ii) the pre-mixing time interval between precursor/reducing agent mixing and injection of the mixture in the MW cavity (tpre−mix) and (iii) the residence time in the MW cavity (tr) were investigated to optimize the reaction conversion efficiency (𝜂c) and the electrochemical performance of the synthesized electrocatalysts. The value of 𝜂c was impressively increased from 52% to ~ 98% by changing the value of tr from 2.4 min to 4.7 min while keeping all other parameters constant. The Ir-IrOx electrocatalysts synthesized under optimal synthesis conditions demonstrate an excellent OER mass activity of 351 A g−1 compared to that of 305 A g−1 for the commercial IrO2. During a potentiodynamic accelerated stress test (AST), the synthesized electrocatalysts show an electrochemical stability comparable to or higher than that of the commercial IrO2. The Ir-IrOx sample having the optimal OER performance exhibited an OER activity retention of 40% compared to 31% for the commercial IrO2. Longer tr and additional MW exposure of the reaction bath was found to decrease the oxidation number of the Ir-IrOx surface efficiently, enhancing both the OER activity and durability of the synthesized Ir-IrOx sample.