Carbon nanotube : supported bimetallic nanocatalysts for the electro-oxidation of alcohols in alkaline media

Abstract

An electrocatalyst plays an important role in the alcohol oxidation reaction in fuel cells. Palladium based electrocatalysts are one of the promising candidates for alcohol oxidation in direct alcohol alkaline fuel cells. This study reports the preparation of metal nanoparticles (Pd, Ni, and Sn) supported on sulfonated multi-walled carbon nanotubes (SF-MWCNTs) using a microwave-assisted solvothermal method. The physical properties of the prepared electrocatalysts were investigated using several techniques such as TEM, EDX, XRD, FTIR and Raman spectroscopy. The electrocatalytic behaviour of the SF-MWCNT-Pd and its mixtures (i.e., SF-MWCNT-PdSnmix and SF-MWCNT-PdNimix) towards ethanol and ethylene glycol oxidation in alkaline medium were investigated. The results show that the mixed Pd-based catalysts gave better electrocatalytic activity than their alloy nanoparticles or Pd alone. The SF-MWCNT platform gave better electrocatalytic performance compared to the unsulfonated and commercial vulcan carbon. Detailed electrochemical studies (involving cyclic voltammetry, chronoamperometry, chronopotentiometry, and impedance spectroscopy) prove that the electrocatalytic oxidation of ethanol at the SF-MWCNT-PdNimix platform is more stable, occurs at lower potential, and gives lower Tafel slopes, with faster charge-transfer kinetics compared to its SF-MWCNT-PdSnmix counterpart. The results also revealed that SF-MWCNT-PdNimix is more tolerant to CO poisoning than the SF-MWCNT-PdSnmix during ethanol oxidation in alkaline medium. However, the SF-MWCNT-PdSnmix electrocatalyst showed better electrocatalytic behaviour for ethylene glycol oxidation in alkaline medium; with high current response, better stability and low Tafel slopes. Both (SF-MWCNT-PdNimix and SF-MWCNT-PdSnmix) electrocatalysts showed comparable behaviour towards CO poisoning during ethylene glycol oxidation in alkaline medium. The results obtained provide some important insights into the electrochemical response of microwave synthesised Pd-based bimetallic catalysts for potential application in direct alcohol alkaline fuel cell technology.