Ionic Conductivity Measurements—A Powerful Tool for Monitoring Polyol Reduction Reactions

Abstract

The reduction of metal precursors during the polyol synthesis of metal nanoparticles was monitored by ex situ ionic conductivity measurements. Using commonly used platinum precursors (KPtCl, HPtCl, and KPtCl) as well as iridium and ruthenium precursors (IrCl and RuCl), we demonstrate that their reduction in ethylene glycol at elevated temperatures is accompanied by a predictable change in ionic conductivity, enabling a precise quantification of the onset temperature for their reduction. This method also allows detecting the onset temperature for the further reaction of ethylene glycol with HCl produced by the reduction of chloride-containing metal precursors (at ≈120 °C). On the basis of these findings, we show that the conversion of the metal precursor to reduced metal atoms/clusters can be precisely quantified, if the reaction occurs below 120 °C, which also enables a distinction between the stages of metal particle nucleation and growth. The latter is demonstrated by the reduction of HPtCl in ethylene glycol, comparing ionic conductivity measurements with transmission electron microscopy analysis. In summary, ionic conductivity measurements are a simple and straightforward tool to quantify the reduction kinetics of commonly used metal precursors in the polyol synthesis.

Extending the Polyol Reduction Process into the Second Dimension: Oxide Thin Film Reduction

“…While the oxidation of EG during the polyol process follows a much more complex reaction pathway. [40][41][42] such calculations provide a useful indication of what might thermodynamically be possible. Thus, the Gibbs free energies of the reduction of three metal oxides (tin, nickel, and tantalum oxides) using EG were calculated as a function of temperature D G T red ( ( )) under otherwise standard conditions (pressures/activities) using the standard enthalpy of formation D AE H f i ( ) for the reactants and the standard entropy AE S i ( ) for each compound at 25 °C, assuming that the entropy term is not a function of temperature within the investigated temperature range (Eq.…”

In Situ Small-Angle X-ray Scattering Studies on the Growth Mechanism of Anisotropic Platinum Nanoparticles

“…For this reason, it is difficult to find studies on the formation mechanism of gold NPs under high-temperature conditions. However, in situ studies on the formation process of platinum NPs under high-temperature reactions have been reported elsewhere. − The reaction temperature and pressure strongly influence the structure, size, and shape of the NPs. , However, to the best of our knowledge, the effect of synthetic protocols on the seed-mediated colloid growth method of platinum NPs, such as heating temperature, time, and rate, on the shape, size, number density, reaction yield, and specific surface area (SSA) of platinum NPs has not yet been investigated for fuel cell applications.…”

Effect of Solvent Ratio (Ethylene Glycol/Water) in the Synthesis of Pt/C Cathode Catalysts on PEM Fuel Cell Performance

“…9,10 Nowadays, the polyol process, or variations of it, are frequently used to prepare a variety of supported metal catalysts, [11][12][13][14][15][16][17] including cathode catalysts for PEMFC applications. 18,19 pH or rather a concentration-independent fixed ratio of NaOH to Pt precursor (H 2 PtCl 6 ) have direct influence on the size of Pt nanoparticles obtained by the polyol process. Quinson et al used a NaOH to Pt precursor ratio of 3 to 25 in the synthesis, which translates to an initial pH value of ∼10 to 14 before the reduction of the metal precursor.…”