Noble Transition Metal Oxides Research Articles

Electrochemical Studies of Lanthanum Ruthenates Towards the Oxygen Evolution Reaction in Alkaline Media

Among the fundamental challenges for enabling metal-air batteries and fuel cells is the oxygen electrocatalysis at the so called air-cathode. Numerous research work has been carried out on the synthesis of new cathode materials in order to reduce the voltage loss associated with the oxygen reactions. ORR and OER have proven to be catalytic dependent electrochemical processes, and thus, the catalytic material at the oxygen-consuming electrode plays an important role in the performance of such technologies.Current catalysts used for air cathodes can be classified into noble metals and metal alloys, carbons, and transition metal oxides. Platinum and carbonaceous electrodes such as Pt-nanopartices dispersed on graphene have been the primary choice to catalyze the ORR because of their known superior electrocatalytic activity. However, carbonaceous materials are poorly stable anodically and readily decompose to oxidize carbon. On the other hand, the oxygen evolution reaction shows little activity on carbonaceous materials, and hence transition metal oxides and noble transition metal oxides are being studied for these purposes. Lanthanum cobalt oxides [1] and lanthanum nickelates [2] of the form ABO3, have also shown promising catalytic activities and good stability. In the present, the electrochemical performance of ruthenium as B site element is studied. Compared with other platinum group metals, ruthenium has exhibited remarkably oxygen evolution activities in alkaline media [3]. A group of lanthanum ruthenate materials including LaRuO3 and La2RuO5 have been synthesized, characterized and studied for oxygen electrode applications. The ruthenate compounds were synthesized by the well-known Pechini polymerization method. All the samples were characterized by XRD for phase analysis and XPS for valence state determination. For the electrochemical measurements, a traditional three-electrode cell was employed. The working electrode consisted of a modified glassy carbon disk with a catalyst ink. The ink was prepared by mixing a predetermined amount of the catalytic powder with poly(vinylidene fluoride) in a ratio of 80:20 and dispersed in n-methyl-2-pyrrolidinone.Electrochemical performance has been investigated by means of steady state current measurements and cyclic voltammetry. Figure 1 (a) and (b) shows the XRD spectra for the monoclinic La2RuO5 compound and the steady state current measurements for both ruthenates, respectively. The XRD model used is a PANalytical X’Pert Powder diffractometer using Cu kα radiation with a wavelength of 1.54056 Å. Acknowledgements This work is supported by the IGERT-NSF fellowship and partially funded by the US Department of Energy/NETL Oak Ridge Institute for Science and Education (ORISE) fellowship.

Electrochemical capacitors utilising transition metal oxides: an update of recent developments

Transition metal oxides receive considerable attention in the area of electrochemistry not only due to their beneficial reported structural, mechanical or electronic properties, but because of their capacitive properties ascribed to their multiple oxide states they exhibit pseudo capacitances which carbon counterparts generally cannot. Typically transition metal oxides may be classified as noble transition metal oxides which exhibit excellent capacitive properties but have the drawback of generally being relatively expensive. Alternatively base metal oxides may also be utilised which are considerably cheaper and more environment friendly than noble transition metals as well as exhibiting good capacitive properties. In considering that nanostructured materials can help ameliorate the electrochemical performances of transition metal oxides, this review summarizes the recent investigations of fundamental advances in understanding the electrochemical reactivity of transition metal oxides, thus leading to an improved capacitive performance, which is essential for their continual use in a plethora of supercapacitor applications.

Growth and equilibrium morphology of metal precipitates formed inside an oxide matrix

Metal precipitation occuring during internal reduction of various mixed oxides, such as magnesia or alumina, doped with more noble transition metal oxides, is investigated for different doping contents, reaction temperature and driving forces. The precipitate morphology developing inside the solid oxide matrix and the corresponding orientation relationships between the metal and the oxide phase are analysed by transmission electron microscopy. The evolution of precipitate shape across the reduction scale is interpreted in terms of ageing of the metal inclusions; the various morphologies identified are ascribed to different stages of nucleation, diffusional growth and final equilibration.