Gold nanoparticles (Au NPs) and gold-based nanomaterials combine unique properties relevant for medicine, imaging, optics, sensing, catalysis, and energy conversion. While the Turkevich–Frens and Brust–Schiffrin methods remain the state-of-the-art colloidal syntheses of Au NPs, there is a need for more sustainable and tractable synthetic strategies leading to new model systems. In particular, stabilizers are almost systematically used in colloidal syntheses, but they can be detrimental for fundamental and applied studies. Here, a surfactant-free synthesis of size-controlled colloidal Au NPs stable for months is achieved by the simple reduction of HAuCl4 at room temperature in alkaline solutions of low-viscosity mono-alcohols such as ethanol or methanol and water, without the need for any other additives. Palladium (Pd) and bimetallic Au x Pd y NPs, nanocomposites and multimetallic samples, are also obtained and are readily active (electro)catalysts. The multiple benefits over the state-of-the-art syntheses that this simple synthesis bears for fundamental and applied research are highlighted.

The concept of combining electrical impedance spectroscopy (EIS) with environmental transmission electron microscopy (ETEM) is demonstrated by testing a specially designed micro gadolinia-doped ceria (CGO) sample in reactive gasses (O 2 and H 2 /H 2 O), at elevated temperatures (room temperature-800 °C) and with applied electrical potentials. The EIS-TEM method provides structural and compositional information with direct correlation to the electrochemical performance. It is demonstrated that reliable EIS measurements can be achieved in the TEM for a sample with nanoscale dimensions. Specifically, the ionic and electronic conductivity, the surface exchange resistivity, and the volume-specific chemical capacitance are in good agreement with results from more standardized electrochemical tests on macroscopic samples. CGO is chosen as a test material due to its relevance for solid oxide electrochemical reactions where its electrochemical performance depends on temperature and gas environment. As expected, the results show increased conductivity and lower surface exchange resistance in H 2 /H 2 O gas mixtures where the oxygen partial pressure is low compared to experiments in pure O 2 . The developed EIS-TEM platform is an important tool in promoting the understanding of nanoscale processes for green energy technologies, e.g., solid oxide electrolysis/fuel cells, batteries, thermoelectric devices, etc.

Establishing a stable and well conducting contacting material is critical for operando electron microscopy experiments of electrical and electrochemical devices at elevated temperatures. In this contribution, the nanostructure and electrical conductivity of ion beam deposited Pt are investigated both in vacuum and in oxygen as a function of temperature. Its microstructure is relatively stable up to a temperature of approx. 800°C and up to an applied current density of approx. 100 kA/cm2. Its conductivity increases with temperature, attributed to densification, with changes in the hydrocarbon matrix being less important. Recommendations are provided with respect to the Pt deposition parameters in terms of maximizing stability and minimizing electrical resistance. Research Highlights It is feasible to use ion beam deposited Pt as electrical contacting material in operando electron microscopy. The deposited Pt is relatively stable up to 800°C and approx. 100 kA/cm2. The resistivity can be reduced by increasing the applied ion current during deposition and by thermal annealing at a temperature of 500°C in a few mbar of oxygen.

Gold nanoparticles (AuNPs) and gold-based nanomaterials combine unique properties relevant for medicine, biomedical applications, imaging, optics, sensing, catalysis or energy conversion. While the Turkevich-Frens and Brust-Schiffrin methods remain the state-of-the-art colloidal syntheses of AuNPs, there is a need for more sustainable and tractable strategies. Here, a reproducible and scalable surfactant-free synthesis of stable colloidal AuNPs with multiple benefits is achieved by the simple reduction of HAuCl4 at room temperature in alkaline solutions of mono-alcohols and water. A parametric study including more than 350 experiments shows that mixing different alcohols is a simple strategy for achieving size control in the range 6-30 nm in diameter and the order of addition of the chemicals strongly affects the outcome of the synthesis. The synthesis method also applies to surfactant-free palladium (Pd) and bimetallic AuxPdy NPs, nanocomposites and multi-metallic samples, all readily active (electro)catalysts. The simple synthesis bears promising features for fundamental and applied research.

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