Cryogels from Pt/γ-Fe2O3 and Pd/γ-Fe2O3 NPs as Promising Electrocatalysts for Ethanol Oxidation Reaction

Abstract

Cryogels from noble metal NPs have proven to be highly efficient catalysts due to their high specific surface area which increases the mass transfer channels and catalytic active sites. By using metal oxides as co-catalysts, the costs of the material can be significantly reduced, while the catalytic activity can remain the same or even improve due to synergetic effects. In this work, we synthesize different cryogel thin films supported on modified ITO substrates from Pt, Pd nanoparticles (NPs), and mixtures of these noble metals with γ-Fe2O3 NPs in a very low concentration (1 wt% of the noble metal). Structural and elemental analysis of the samples are performed, along with the measurement and analysis of their catalytic activity. The electrocatalytic activity of the cryogels towards ethanol oxidation reaction (EOR) in alkaline media was evaluated by means of cyclic voltammetry. By mixing γ-Fe2O3 NPs with Pt or Pd NPs in the cryogel structure, we observe increased tolerance against poisonous surface intermediates produced during the EOR. Moreover, we observe an increase in the catalytic activity towards EOR in the case of the 1 wt% Pd/γ-Fe2O3 cryogel, making them promising materials for the development of direct ethanol fuel cells.

Nanoparticle‐Based Cryogels from Colloidal Aqueous Dispersion: Synthesis, Properties and Applications

“…[21] In contrary, mixing NPs of different sizes and opposite surface charge leads to homogenous distribution in the cryogel structure. [21,87] The TEM images in Figure 5c showcase the influence of the surface charge of the NPs on the final homogeneity of the multicomponent cryogel structures.…”

“…[16,22,28,77,82] All of these studies paved the way to the works in 2014 and 2016 of cryogels from inorganic nanocrystals in aqueous solutions, which is the main focus of this review. [83,84] The cryogelation by freezing and freeze-drying directly of an aqueous nanocrystal solution is thoroughly investigated by our group [84][85][86][87] obtaining self-supported porous networks from different nanoparticle systems, i. e. Au, Ag, Pd, Pt, hematite Fe 2 O 3 , and CdSe/CdS rods, with densities ranging from 20-60 mg/cm 3 (around 0.2 % of the density of the bulk materials). Among the advantages there are the fast and easy preparation method, without chemical selectivity, no need of previous hydrogelation and it can be used for any nanoparticle system as long as it is in water and with a nanoparticle concentration (nanoparticle volume fraction) of at least 0.1 %, otherwise the structure collapses and shrinks.…”

“…Generally, the particles are not fused together but they are very close on the atomic scale to allow charge carrier movement along the structure (Figure 3c). [86,87] This is highly interesting because the macroscopic structure of the cryogels can still retain the nanoscopic properties of the NPs. The 3D selfsupporting structure is highly porous with large surface to volume ratio, the pores are formed in between the NPs within the 2D sheets (nanopores) and in between the 2D sheets (micropores) (Figure 3d and 3e), [87] the overall scaffold can be described as a sponge like voluminous structure.…”

“…[85,109] Multicomponent cryogels can be obtained by mixing aqueous colloidal solution of different types of NPs followed by freezing (Figure 5a). [21,86,87] The advantage of mixing multiple types of NPs in the same cryogel structure is to obtain novel materials with improved properties. For example, Pt, Au or Ag were mixed with metal oxides and Au or Ag were mixed with hematite to obtain multicomponent cryoaerogel monoliths (Table 1).…”

“…[86] Moreover, cryoaerogels from mixed Pt or Pd with ϒ-Fe 2 O 3 NPs were prepared as thin films supported on conductive ITO/glass substrates (Figure 5a). [87] It is challenging yet important to obtain multicomponent cryogels with homogenous distribution of the NPs throughout the gel structure. The arrangement of the NPs within the multicomponent cryogel can be influenced by the ζ-potential of the NPs in the aqueous colloidal solution.…”