Palladium Supported on 3D Graphene as an Active Catalyst for Alcohols Electrooxidation

Abstract

In the present study, highly porous 3D-Graphene nanosheets (3D-GNS) were synthesized using the Sacrificial Support Method (SSM) and utilized as a support for palladium (Pd) nanoparticles. The Pd nanoparticles were deposited using the original Pd-precursor based Soft Alcohol Reduction Method (SARM) with different alcohols. The obtained materials were comprehensively characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (SEM). Chemically reduced Pd/3D-GNS catalysts were then studied for the electrochemical oxidation of ethanol and methanol in alkaline media. Our study shows that combination of SSM and SARM-EtOH fabrication process allowed obtaining materials with a smaller particle size distribution and a higher surface area (yielding better utilization of Pd), as well as the highest electrochemical activity and durability, with a peak current density of over 1100 A/g Pd for ethanol electrooxidation. The usage of liquid fuels and anion-exchange membranes (AEM) has substantial advantages in comparison to the hydrogen-fed protonexchange membrane technology. For example, liquid fuels have higher gravimetric and volumetric energy densities where the logistics of fuel delivery are much simpler in comparison to compressed hydrogen. Moreover, the electro-oxidation kinetics for many liquid fuels is enhanced in alkaline environment. Note also that the oxygen reduction reaction (ORR) kinetics is faster in alkaline media than in acidic ones, and that the migration of OH − anions from the anode to the cathode compartment of the fuel cell results in a reduced crossover of liquid fuels. These advantages enable to use relatively cheaper nonprecious materials for both anodes and cathodes 9 have been reviewed by Antolini et al. 8 The higher activity of Pd and Pd-based catalysts in alkaline media for alcohols electrooxidation reaction in comparison to platinum (Pt) is well-established and reviewed by several research groups. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] In order to better utilize the Pd nanoparticles, supported and nanostructured catalysts should be used. The support should meet certain requirements such as a high surface area, excellent electrical conductivity, and provide good contact to the metal nanoparticles. Presently, carbonaceous materials such as carbon blacks, nanotubes, nanofibers, etc. are of the most extensively used materials for catalytic support; however, the majority of these carbon supports have a substantial amorphous component, which is less conductive than graphite and presents durability issues. 24 On the other hand, highly graphitic materials usually have a low surface area. The common problem for both amorphous and graphitic materials is the weak interaction of noble metal nanoparticles with the surface, which eventually leads to particle detachment and a decrease in the catalyst durability (see e.g. [24][25][26][27][28] ) In order to overcome these limitations, we report the synthesis of highly defect...

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“…Oxalate decarboxylase (OxDC) is an enzyme found in nature and converts oxalic acid to formic acid in wooddecaying fungi and bacteria. [30] The same Pd/3D-GNS catalysts were used in this research to oxidize formic acid and the cyclic voltammogram of this reaction is shown in the Supplementary Information ( Figure S4, SI). [26,27] Here, recombinant OxDC from Bacillus subtilis was used to convert mesoxalic acid to glyoxylic acid and oxalic acid to formic acid by breaking their CÀ C bonds.…”

“…[6,29] Palladium nanoparticles supported on 3D graphene nanosheets (Pd/3D-GNS) have been shown to be active for alcohol electrooxidation. [30] The same Pd/3D-GNS catalysts were used in this research to oxidize formic acid and the cyclic voltammogram of this reaction is shown in the Supplementary Information ( Figure S4, SI).…”

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