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.

Abstract Continuous solvothermal syntheses of carbon-based nanomaterials (CBNs) provide an efficient route to generate optically active substances compared to batchwise synthesis. In this study, technical process control and in-line analytical data acquisition was applied. Both facilitated immediate insight into the product’s properties in correlation to the process parameters. As a second continuous step, spray-drying, converted the CBNs dispersions into powder materials to increase the density and simplify product handling, in addition minimizing self-quenching of the fluorescent properties. As starting materials, phenylenediamine regioisomers were chosen which are conventionally explored via autoclave synthesis. For each regioisomer, two emission wavelength regions appeared in the visible wavelength range. The residence time, temperature, acidic component and initial starting concentration played a significant role in the relative emission intensities concluded from systematic screening. While the resulting materials need further improvement concerning their photo stability and absolute emission intensity, the technological combination presented here is a step towards the tailor-made manufacturing chain of CBNs based on micro-process engineering and continuous flow syntheses at safe high-pressure conditions.