The wet-chemical synthesis of hollow graphitic spheres, a highly defined model catalyst support for electrocatalytic processes, is laborious and not scalable, which hampers potential applications. Here, we present insights into the chemical vapor deposition (CVD) of ferrocene as a simple, scalable method to synthesize hollow graphitic spheres (HGS cvd ). During the CVD process, iron and carbon are embedded in the pores of a mesoporous silica template. In a subsequent annealing step, iron facilitates the synthesis of highly ordered graphite structures. We found that the applied temperature treatment allows for controlling of the degree of graphitization and the textural properties of HGS cvd . Further, we demonstrate that platinum loaded on HGS cvd is significantly more stable during electrochemical degradation protocols than catalysts based on commercial high surface area carbons. The established CVD process allows the scalable synthesis of highly defined HGS and therefore removes one obstacle for a broader application.

Proton-exchange membrane fuel cells (PEMFCs) represent an essential technology for the future decarbonization of the transportation sector. A major component of PEMFCs is the catalyst, often Pt-based alloys supported on carbon black, which are sufficiently active and stable upon long-term operation under the harsh reaction conditions implied by PEMFCs. However, the catalyst synthesis is typically laborious and challenging to upscale, employing organic solvents, surfactants, or uneconomical metal deposition routes. To solve this, we offer a mechanochemically assisted two-step solvent-less methodology to produce supported metal catalysts, particularly supported PtNi and PtCo catalysts. Accordingly, metal salts are first dispersed on the designated support by planetary ball milling. Subsequently, the mixture is reduced with hydrogen and annealed under an inert atmosphere to yield supported alloyed nanoparticles. Notably, by applying our procedure to the synthesis of carbon-supported PtNi and PtCo nanoparticles, we demonstrate that size, composition, and total metal loading can be finely adjusted, leading to highly performant catalysts in the oxygen reduction reaction (ORR).

The copper-catalyzed electrochemical CO 2 reduction reaction represents an elegant pathway to reduce CO 2 emissions while producing a wide range of valuable hydrocarbons. The selectivity for these products depends strongly on the structure and morphology of the copper catalyst. However, continued deactivation during catalysis alters the obtained product spectrum. In this work, we report on the stabilizing effect of three different carbon supports with unique pore structures. The influence of pore structure on stability and selectivity was examined by high-angle annular dark field scanning transmission electron microscopy and gas chromatography measure-ments in a micro-flow cell. Supporting particles into confined space was found to increase the barrier for particle agglomeration during 20 h of chronopotentiometry measurements at 100 mA cm À 2 resembling long-term CO 2 reduction conditions. We propose a catalyst design preventing coalescence and agglomeration in harsh electrochemical reaction conditions, exemplarily demonstrated for the electrocatalytic CO 2 reduction. With this work, we provide important insights into the design of stable CO 2 electrocatalysts that can potentially be applied to a wide range of applications.[a] E.

Supported bimetallic catalysts composed of platinum and transition metals are highly investigated electrocatalysts for the oxygen reduction reaction (ORR) because of their enhanced activity and stability. However, common routes to synthesize these materials are often laborious and not scalable, employing organic solvents or uneconomical metal deposition methods [1-2]. Here, we present a mechanochemistry-assisted, dry and scalable synthesis route towards supported bimetallic catalysts, which consists of only two steps: First, metal salts are dispersed on a carbon support in a planetary mill without further additives. Following, the powder is reduced with hydrogen and annealed to yield alloyed catalysts. With this process, we are able to synthesize PtM/C catalysts where M was Ni, Co or Ru. Both metal loading and ratio could be adjusted by changing the amount of metal salt. The average size of the PtM-NPs was similarly controlled by changing the annealing temperature. With X-ray diffraction (XRD), we show that no metal or salt reflexes are present after milling and that the XRD pattern matches the carbon support. After reduction and annealing, clear reflexes of the targeted alloy composition are visible. The latter was confirmed by scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDX). After milling, ionic metal species are present as sub-nanometer clusters evenly dispersed over the carbon support. After reduction and annealing, PtM nanoparticles have formed. Neither by XRD nor by STEM-EDX was the presence of unalloyed Pt or M detected. Optical emission spectrometry was used to confirm the targeted loading and bulk composition of the catalysts. Due to the known high activity for catalyzing the ORR, PtNi/C and PtCo/C were subjected to electrochemical evaluation in a rotating disc electrode setup [2]. In both cases, specific activities surpassing 1 mA/cm2 Pt at 0.9 V were reached. The electrochemically active surface area (ECSA) and mass activity were also in the range expected for the composition and particle size. To assess the stability, the catalysts were cycled from 0.4 to 1.0 V (RHE) with a scan rate of 1 V/s for 10800 cycles. The loss in ECSA of approximately 5 % was also in line with expectations. Since iron impurities are known to reduce the lifetime of a proton exchange membrane fuel cell, the milling process was adapted to a Si3N4-mill instead of a steel mill, again demonstrating the flexibility of this synthesis route [3]. To conclude, the reported solid-state procedure allows the dry synthesis of supported bimetallic catalysts over a wide range of compositions. The materials show high activity and stability catalyzing the ORR. Due to its simplicity and flexibility, we expect this synthesis approach to be applied in other fields of catalysis within a short period of time. References: [1] K. Loza, M. Heggen, M. Epple, Adv. Funct. Mater., 2020, 30, 1909250. [2] I. E. L. Stephens, A. S. Bondarenko, U. Grønbjerg, J. Rossmeisl and I. Chorkendorff, Energy Environ. Sci., 2012, 5, 6744. [3] A. Collier, H. Wang, X. Z. Yuan, J. Zhang, D. P. Wilkinson, Int. J. Hydrog. Energy, 2006, 31, 1838–1854. [4] J. De Bellis, M. Felderhoff, F. Schüth, Chem. Mater., 2021, 33, 6, 2037–2045. Figure 1

No abstract