Gold and Platinum Decorated Iron Oxides As Efficient Overall Water Splitting Catalysts

Abstract

Transition metal oxides (TMOs) have gained much interest due their water splitting properties, producing oxygen and hydrogen as a clean source of energy, with the possibility of replacing fossil fuels for the future energy demands. Iron, Cobalt, Nickel and their oxides/oxyhydroxides have been investigated extensively due to their cost effectiveness and applicability in catalysing the water-splitting reaction, although there are some issues with performance degradation. In particular, recent studies on mixed metal oxides of Ni, Fe and Co show enhanced performance for oxygen and hydrogen production compared to the single metallic component.[1] Iron oxides do not show good activity for the OER or the HER but are attractive for such an application if their activity can be enhanced given the low cost of such materials. Interestingly, it has been shown that fast active sites at FeOOH are responsible for enhanced OER activity within the mixed oxide system of Ni and Co.[2] A more recent development is the pursuit of bifunctional materials that can catalyse both the OER and HER which is attractive from a commercial viewpoint and electrolyser manufacturing. Again if Fe based materials can be used for this reaction, it would be highly beneficial.In this work we galvanically replace iron and iron hydroxide nanostructures with Pt and Au and investigate the catalyst for both the OER and HER in an alkaline environment. The decoration of the iron surface with a low concentration of Pt or Au results in significantly increased activity for both the HER and more surprisingly the OER. The increased HER activity is expected as Pt is an excellent HER catalyst, however the presence of Au was also found to provide excellent performance. Although both Pt and Au are poor materials for the OER, they promote the reaction at iron oxide. To date, there have been no reports showing Au or Pt decorated Iron oxides that can split water effectively. The material was characterised using Scanning Electron Microscopy coupled with field emission spectra (SEM), Grazing Incidence X-ray Diffraction (GIXRD), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). The SAED and Dark Field Scanning Transmission Electron microscopy (DF-STEM) indicating that Au or Pt decorates the surface of the core polycrystalline nanocubes of iron. After the OER, a core-shell structure of Au-FeOOH or Pt-FeOOH is realised which is an effective bifunctional electrocatalyst that can catalyse both the OER and HER.[1] aM. S. Burke, L. J. Enman, A. S. Batchellor, S. Zou, S. W. J. C. o. M. Boettcher, 2015, 27, 7549-7558; bM. Görlin, P. Chernev, J. Ferreira de Araújo, T. Reier, S. r. Dresp, B. Paul, R. Krähnert, H. Dau, P. Strasser, Journal of the American Chemical Society 2016, 138, 5603-5614.[2] Z. Liang, H. S. Ahn, A. J. Bard, Journal of the American Chemical Society 2017, 139, 4854-4858. Figure 1