Rhiyaad Mohamed

Thermodynamic explanation of the universal correlation between oxygen evolution activity and corrosion of oxide catalysts

In recent years, the oxygen evolution reaction (OER) has attracted increased research interest due to its crucial role in electrochemical energy conversion devices for renewable energy applications. The vast majority of OER catalyst materials investigated are metal oxides of various compositions. The experimental results obtained on such materials strongly suggest the existence of a fundamental and universal correlation between the oxygen evolution activity and the corrosion of metal oxides. This corrosion manifests itself in structural changes and/or dissolution of the material. We prove from basic thermodynamic considerations that any metal oxide must become unstable under oxygen evolution conditions irrespective of the pH value. The reason is the thermodynamic instability of the oxygen anion in the metal oxide lattice. Our findings explain many of the experimentally observed corrosion phenomena on different metal oxide OER catalysts.

Facile deposition of Pt nanoparticles on Sb-doped SnO2 support with outstanding active surface area for the oxygen reduction reaction

Understanding the influence of the support on the electrocatalytic behaviour of platinum is key to the development of novel Pt/oxide catalysts for the oxygen reduction reaction (ORR). For studies to isolate these effects, highly dispersed supported Pt nanoparticles with well-controlled particle sizes are required. In this study, we demonstrate a novel preparation process for Pt/oxide catalysts, with small Pt nanoparticles (2.5–3.5 nm), supported on a commercial Sb–SnO2 (ATO) nanopowder, with a very high utilization of the Pt-precursor. The organometallic chemical deposition method produces catalyst nanoparticles with a homogeneous distribution over the surface of the support even at high Pt metal loadings. Additionally, by using a mild hydrogen reduction treatment of the oxide support prior to Pt deposition, significantly smaller Pt nanoparticles were obtained with an outstanding mass-specific electrochemically active surface area exceeding 100 m2 g−1. Furthermore, by varying the Pt metal loading, several fundamental electrocatalytic effects that strongly influence the Pt/ATO system were distinguished. Good electrochemical stability during high-potential cycling was observed and was attributed to potential-dependent in situ conductivity switching of the ATO support. In turn, ORR activities of the Pt/ATO catalysts were found to be influenced by a combination of Pt particle size effects, ATO support in situ conductivity limitations at PEFC operation potentials, and electrocatalytic metal–support interactions. Therefore, in addition to demonstrating a powerful method for the preparation of exceptionally high surface area Pt/oxide catalysts, the present study contributes to the detailed understanding of the interplay between various phenomena that influence the electrocatalytic activity and stability of Pt/oxide systems for the ORR. Furthermore, the novel preparation approach for Pt/metal oxide catalysts could be of major interest for catalyst preparation in other fields of electrocatalysis and heterogeneous catalysis.