Electrochemical valorization of crude glycerol in alkaline medium for energy conversion using Pd, Au and PdAu nanomaterials

Crude glycerol is a byproduct from biodiesel production, and due to overproduction, new applications requiring the minimum purification steps are needed. The electrochemical valorization of crude glycerol is one of the most attractive applications. In this work, the use of crude glycerol as fuel for energy conversion applications was studied on noble materials such as Pd/C, Au/C and PdAu/C nanoparticles with different Pd/Au atomic composition (1:1, 3:1 and 5:1) with the aim of identifying the main barriers to improve the crude glycerol electro-oxidation reaction (crude GOR). High-resolution transmission electron micrographs revealed that Pd and PdAu nanoparticles had average sizes below 10 nm, while Au nanoparticles had particle sizes of 16.2 +/- 1.4 nm. Besides, crude glycerol was obtained from a biodiesel prepared by a transesterification reaction assisted by sonication, resulting in a crude glycerol with a high glycerol content (> 95 V/V %). The electrocatalytic evaluation indicated that Pd5Au1/C was the material with the highest current density for crude GOR, displaying 140.1 mA mg(PdAu)(-1), which was 1.8, 2.73, 2.79, 4.14 and 2.2 times higher to that obtained for Pd3Au1/C, Pd/C, Au/C, Pd1Au1/C, and commercial Pd/C, respectively. Moreover, this current density was 20% higher to that obtained for analytical grade glycerol, which was attributed to the bimetallic capability of Pd5Au1 to oxidize both, glycerol and methanol presented in crude glycerol. In summary, it was found that the competition between the adsorption of methanol and glycerol on active sites plays a major role on the activity for crude GOR.