Chemical Vapor Deposition of Hollow Graphitic Spheres for Improved Electrochemical Durability

Abstract

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.

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO2 Reduction

“…As the third support material, we synthesized mesoporous graphitic spheres with an apparent SSA of 2000 m 2 g −1 and 2 mL g −1 in pore volume. The employed hard‐templating method allows for precise control of the pore form and size distribution with high reproducibility [22] . The type IVa isotherm and H1‐like hysteresis loop indicate a carbon material with a defined, ink‐bottle‐shaped mesopore network.…”

“…The chemical vapor deposition (CVD) synthesis of the mesoporous graphitic spheres was carried out as reported by Knossalla et al [22] . For the synthesis of the SiO 2 hard template 450 mL of ethanol, 72 mL of water, and 17.4 mL of 25 wt.% ammonium hydroxide solution was mixed.…”

Catalyst Stability in Aqueous Electrochemistry

“…Particles embedded into a protecting pore structure agglomerate to a much lower degree compared to particles on the surface of outer supports. Engineering the embedding pore structure allows the local separation of individual particles, and agglomeration is effectively avoided. ,− Using hierarchically organized support structures, be it amorphous or crystalline solids, can greatly impact the catalyst’s stability. Another steric protection strategy lies in encapsulating the active catalyst using a thin conductive (oxide) layer.…”

“…82,87 Highly graphitic structures with high surface area and tailored surface porosity can be achieved by, for example, hard templating, where the graphitization proceeds on a previously synthesized template such as silica. 88 The presence of metal particles itself may catalyze carbon corrosion at the solid−solid interface, as shown in Figure 4. 89−91 Functionalization of the carbon support with nitrogen or oxygen may augment the resistance against corrosion.…”

“…Different, mainly amorphous, carbon blacks tend to show similar corrosion rates after surface-area normalization . On the other hand, an increased degree of graphitization leads to carbon corrosion rates two or three times lower than nongraphitized ones, even after surface-area normalization. , Graphitized carbon supports exhibit corrosion rates practically invariant over time compared to those of amorphous carbon supports. , This difference has been attributed to the inhomogeneous distribution of the graphitic planes in nongraphitized carbon supports. , Highly graphitic structures with high surface area and tailored surface porosity can be achieved by, for example, hard templating, where the graphitization proceeds on a previously synthesized template such as silica . The presence of metal particles itself may catalyze carbon corrosion at the solid–solid interface, as shown in Figure . − …”