Bimetallic nanoparticle electrocatalysts for the interconversion of CO₂ and renewable fuels

• Main Author: Humphrey, Jo J. L.
• Published: University of Bristol 2016
• Subjects: 541
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.702927

Bimetallic nanoparticle electrocatalysts were investigated for reactions related to "closing the carbon cycle": C02 reduction, and oxidation of HCOOH and adsorbed CO (COads). Well-defined Au-Pd coreshell nanoparticles were used as a model system to optimise detection protocols for products of C02 reduction. The product distribution was dependent on the applied electrolysis potential and the Pd shell thickness: in pH 4 Na2S04 electrolyte, nanoparticles with a 10 nm shell produced HCOO- with a peak Faradaic efficiency of 27%, as well as hydrocarbons. The reactivity could also be manipulated through reaction conditions: in pH 7 NaHC03, the same nanoparticles generated HCOO- with an efficiency of 31%, while at a commercial catalyst the efficiency reached 91%. The investigation of C02 electroreduction catalysts was extended to Pt and Pt-alloy nanoparticles, for which the latter are explored for the first time. Monodisperse nanoparticles were prepared by colloidal "hot injection". Detailed studies explored the removal of capping ligands from Pt nanoparticles, a crucial step for obtaining a clean surface to study the electrocatalytic reactivity. This included the first TGA-MS study of oleylamine desorption during thermal annealing. Various Pt-alloy nanoparticle electrocatalysts, with a range of atomic compositions, were prepared by the same approach. Pt-Fe and Pt-Co alloys were found to reduce C02 to acetate with good selectivity and Faradaic efficiencies up to 57%, depending on the catalyst composition. The structure and electrocatalytic activity of dealloyed Pt-Fe and Pt-Co electrocatalysts was studied. Catalysts were voltammetrically dealloyed in acidic electrolyte; changes in electrochemical signatures and elemental composition, as well as STEM-HAADF and EELS analyses, indicated the formation of Pt-skin nanostructures due to selective dissolution of Fe or Co. Whilst the bimetallic catalysts did not exhibit improved tolerance to COads, they demonstrated enhanced reactivity towards HCOOH oxidation, with peak current densities up to double those obtained at Pt.