Electrocatalytic oxidation of crude glycerol from the biodiesel production on Pd-M (M = Ir, Ru or Pt) sub-10 nm nanomaterials

Abstract

Crude glycerol (CG) is a by-product from the biodiesel industry; its application in the chemical industry is limited by its complex composition (glycerol, methanol, surfactants, and salts). The electrochemical valorization of CG is a promising alternative for this waste because it can be used without purification. To this end, highly active nanomaterials to carry efficiently its electro-oxidation reaction are needed. Herein, Pd, and PdM (M is a noble metal: Ru, Ir and Pt) bimetallic nanomaterials were obtained to assess the effect of the co-metal on the crude glycerol electro-oxidation reaction (crude GEOR) in alkaline media. For this purpose, the crystallite size, and the particle size (~7 nm), the metal-support ratio (~20 wt%) and the Pd mass composition in the bimetallic nanomaterials (~20 wt%) were kept similar to avoid surface effects. The activity was analyzed varying the fuel and electrolyte concentrations, and the operating temperature. It was found through these experiments that the bimetallic nanomaterials displayed an improvement in the onset potential to oxidize 1.5 M crude glycerol in 1 M KOH, following the trend: PdPt (−0.37 V vs. NHE) > PdRu, PdIr (−0.24 V vs. NHE) > Pd (−0.2 V vs. NHE). Additionally, PdPt achieved the highest current density (jp, 172.29 mA mgPd−1), being 2.8, 1.6 and 2.1 times higher to the achieved for Pd, PdRu and PdIr, respectively. PdRu resulted to be the most stable electrocatalyst maintaining 97% of its starting current after 500 cycles. We found that the capability of PdPt to oxidize glycerol and methanol found in CG without any fuel adsorption/oxidation competition was the reason that this material displayed the highest activity in contrast with Pd and the bimetallic PdIr and PdRu nanomaterials.