Microwave-Assisted Scalable Synthesis of Pt/C: Impact of the Microwave Irradiation and Carrier Solution Polarity on Nanoparticle Formation and Aging of the Support Carbon

Abstract

Microwave-assisted (MW-assisted) synthesis of nanomaterials is a facile method for material development studies involving small-scale synthesis. The method is being explored further toward industrial scale production of nanoparticle catalyst. Here, optimization of the process parameters for a scalable synthesis of Pt/C through a MW-assisted polyol route using (NH4)2PtCl6 as the Pt precursor has been presented. Further, the impact of MW-irradiation on the carbon support surface structure and its effect on the electrochemical stability of the synthesized Pt/C have been explored. Pt/C electrocatalysts were synthesized using a MW synthesizer in an open system configuration. Effects of different process parameters, namely, solvent composition and hence solvent polarity, reaction time, and Pt precursor concentration on the structure and the electrochemical performance of the synthesized Pt/C catalysts were studied. A mixture of water and ethylene glycol with a water content of 30% v/v was found appropriate for achieving Pt nanoparticles with a particle size of ∼2 nm, suitable for a high electrochemically active surface area (ECSA) of ∼75 m2/gPt. Pt concentrations higher than 5 mM were found unsuitable due to incomplete reduction of the Pt precursor. The minimum reaction time for complete reduction of the Pt precursor was observed to be 400 s. However, increasing the MW treatment time beyond 400 s leads to growth of the Pt nanoparticles and hence reduction in ECSA. Porosity and surface area analysis suggests decreased pore size and surface area of the carbon support by the MW-irradiation during Pt/C synthesis. Hence, the initial electrochemical double layer capacitance (DLC) decreases with increasing MW-irradiation time, leading to the increased surface corrosion and the decreased bulk corrosion of the support carbon, monitored respectively through the relative change in DLC and the evolution of the quinone–hydroquinone redox peak during an accelerated stress test meant for durability assessment of the electrocatalysts.