Isopropanol electro-oxidation on Pt-Ru-Ir: A journey from model thin-film libraries towards real electrocatalysts

Abstract

Liquid fuels are considered a promising alternative to hydrogen in proton exchange membrane fuel cells. In particular, isopropanol, which can be selectively oxidised to acetone and further hydrogenated back to isopropanol using electrochemical and heterogeneous catalysis routes, respectively, opens the possibility of zero-emission fuel cell operation without complex management of molecular H2. However, the maximum electric power of such fuel cells is still relatively low, which is attributed to the poisoning of state-of-the-art Pt-Ru electrocatalysts by adsorbed acetone and/or Ru oxide/hydroxide. Here, in order to mitigate Pt-Ru poisoning at higher anodic potentials during isopropanol oxidation in acidic media, the effect of the addition of Ir, a less oxophilic element than Ru, on the activity and stability during dynamic experiments of Pt-Ru is systematically investigated. To identify the most active compositions, Pt-Ru-Ir thin-film material libraries are prepared using magnetron co-sputtering. The electrocatalytic activity of the libraries is screened using a high-throughput scanning flow cell setup. Catalysts with the highest activity are further synthesised in the form of carbon-supported nanoparticles. Comparing the two systems, similar trends are observed, highlighting the model material libraries being an excellent starting point for novel catalyst development. Besides electrocatalytic activity, catalyst shelf-life and dissolution stability are studied. While significant ageing in the air is found, partial reactivation is possible using a reductive treatment. The dissolution of the most promising nanoparticulate electrocatalyst is evaluated using online inductively coupled plasma mass spectrometry to assess the effect of Ir addition on Pt and Ru stability. No significant stabilising role of Ir, however, is observed. Hence, further optimisation of Pt-Ru or Pt-Ru-Ir is still needed to improve isopropanol fuel cell performance.