Transition Metal (Ni/Cu) Based Bimetallic Catalyst for Glycerol Oxidation

Abstract

Alcohol fuel cell is considered as one of the most promising green energy generation option. Glycerol can be used as a potent fuel because of its excellent energy density, ready availability, financial viability and minimal toxicity. Moreover, glycerol is also an active petroleum by-product. In direct glycerol fuel cell, precious noble metal based catalyst was extensively used as electro-catalyst for glycerol oxidation. The use of noble metal as catalysts restricted the viable commercialisation due to its high cost. This study intended to use transition metal such as nickel and copper based monometallic and bimetallic catalyst for glycerol oxidation to lower down the cost of commercialisation. These metals already proved to be efficient catalyst for electro-oxidation of methanol and ethanol [1-2]. Carbon was already proved to prominent support material for electro-catalyst due to high surface area and superior conductivity.The metals were impregnated into carbon support followed by reduction under H2/Ar environment with 20 wt % metal loading. The weight ratio of Ni and Cu in bimetallic catalyst was fixed as 1:1. The average metal particle size of the catalysts varied between 7.8 to 16.3 nm. The cyclic voltammetry of different catalysts for 0.5 M glycerol oxidation in 1 M KOH is shown in Fig 1a). The onset potential of bimetallic catalyst (NiCu/C) was reduced to 0.20 V compared to their monometallic counterpart (0.39 V for Ni/C and 0.42 for Cu/C). The glycerol oxidation peak was observed at 0.71, 0.73 and 0.78 V for Cu/C, Ni/C and NiCu/C respectively. The specific activity and mass activity was shown in Fig 1b). The highest specific (76 mA/cm2) and mass activity (775 mA/mgmetal) was obtained for NiCu/C from glycerol oxidation. The obtained electrochemical surface area (ECSA) was highest for NiCu/C (99 m2/g) followed by Ni/C (44 m2/g) and Cu/C (34 m2/g). The higher activity of NiCu/C could be attributed to the lower Tafel slope, higher ECSA and charge transfer co-efficient. The EIS results conveyed that electro-oxidation process was slower than charge transfer process. Moreover, lowest time constants for the both the process was observed for NiCu/C catalyst. Hence, NiCu/C proved to be efficient electro-catalyst with superior activity for glycerol oxidation in direct glycerol fuel cell. Fig 1. a) Cyclic voltammetry of different catalyst in 0.5 M glycerol and 0.1 M KOH and b) Specific and mass activity of different catalyst.