Abstract
Palladium nanoparticles supported on carbon Vulcan XC72 (Pd/C) and biocarbon (Pd/BC) synthesized by sodium borohydride process were used as catalysts for ethanol electro-oxidation in alkaline media. The biocarbon (BC) from coconut shell with mesoporous and high surface area (792 m2 g−1) was obtained by carbonization at 900 °C and the hydrothermal treatment in a microwave oven. The D-band and G-band intensity ratio (ID/IG) from Raman analysis showed high disorder of the biocarbon, while X-ray photoelectron spectroscopy (XPS) suggests higher percentage of oxygen groups on the surface of biocarbon than of Vulcan XC72. From X-ray diffraction (XRD), it was observed peaks in 2θ degree related to the face centered cubic (fcc) structure of palladium and the mean crystallite sizes calculated based on the diffraction peak of Pd (220) were 5.6 nm for Pd/C and 5.3 nm for Pd/BC. Using Transmission Electron Microscope (TEM), it was observed particles well dispersed on both carbons support materials. The electrocatalytic activity of the materials was investigated by cyclic voltammetry (CV) and chronoamperometry (CA) experiments. The peak current density (on CV experiments) from ethanol electro-oxidation on Pd/BC was 50% higher than on Pd/C, while the current density measured at 15 min of CA experiments was 80% higher on Pd/BC than on Pd/C. The higher catalytic activity of Pd/BC might be related to the large surface area of the biocarbon (792 m2 g−1) vs (239 m2 g−1) of Vulcan carbon, the defects of the biocarbon structure and higher amount of oxygen on the surface than Carbon Vulcan XC 72.
Highlights
The search for new energy sources based on the concept of clean and renewable energy has been intensified in the recently years [1,2,3]
The result of this work showed that biocarbon from coconut shell is a suitable support for palladium nanoparticles towards ethanol electro-oxidation reaction in alkaline media
Mesoporous of biocarbon was observed in the micrograph from scanning electron microscope (SEM) and according to Transmission Electron Microscope (TEM) micrographs the palladium nanoparticles supported on both carbon support are smaller than 8 nm with very narrow size
Summary
The search for new energy sources based on the concept of clean and renewable energy has been intensified in the recently years [1,2,3]. Fuel cells are pointed out as a promising technology for clean energy generation and its concept is based on the conversion of chemical energy into electricity. It has been reported that the ethanol electro-oxidation kinetic in alkaline media is enhanced compared to the acid media [14, 15]. Catalysts are required to promote ethanol electro-oxidation. Palladium is pointed out as the metal with the highest catalytic activity for ethanol electrooxidation in alkaline media [16,17,18] and catalysts are usually synthesized as nanoparticles in order to increase the surface area which increases the catalytic rate compared to the bulk materials [19, 20]
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