Trends in reactivity of electrodeposited 3d transition metals on gold revealed byoperandosoft x-ray absorption spectroscopy during water splitting

Abstract

electrodepositing Cu, Ni and Co. A combination of operando X-ray absorption spectroscopy and potentiometric control under aqueous conditions revealed the trends in reactivity yielded by these electrodes, which are directly associated with the cross-and overpotentials as well as the occupancy of the 3d orbitals. It was found that under anodic polarization the materials electrodeposited on gold suffer from a lack of stability, while under cathodic polarization they exhibit stable behavior. The observed activity is strongly related to the lack of stability shown by these composites under anodic polarization revealing a dynamic process ruled by corrosion. By operando X-ray absorption, we established that the overall enhancement of the activity for the oxygen evolution reaction is directly attributable to the cross-potential and corrosion process of the electrodeposited materials. It is associated with the high potential deposition, which is the origin of the incipient oxidation-corrosion resistance of the lattice.We conclude that the observed trends in the total current are directly associated with the loss of oxygen in the metal-oxide lattice and the subsequent dissolution of metallic ions in the electrolyte under anodic polarization.reacted O prevents a sustainable catalytic process. The addition of a small amount of metal-oxide, such as titanium or cerium oxides, on top of the Au surface facilitates this rate-determining step and easily continues the catalytic cycle of the production of O2. D e s p i t e t h i s a c t i v a t i o n s t r a t e g y b u l k A u i s a v e r y p o o r c a t a l y s t , b u t A u nanoparticles on metal oxide [3] and carbide [4] materials show unusual catalytic properti es. For exam ple, i t has been shown that CeO2 NPs sm aller than 10 nm dispersed on Au are an excellent catalyst for the water gas shift reaction [5]. In addition, controlling the partial coverage of Au with TiO2 or CeO2 enhances the catalytic activity [6]. Thus, role of size of different Au NPs has been shown as important factor in the catalytic activity [7]. Ideally, one can take advantage of these phenomena and develop highly efficient catalysts by optimizing the Au/metal-oxide synergy. Electrodeposition is an attractive method used to deposit a large variety of materials [8] and allows for precise control of the chemical composition and the structure of the electrodeposited material. However, not all the materials can be electrodeposited in aqueous environment like the alkali metals. Decoding the structure of the electrodeposited electrode, requires the use of advanced spectroscopic methods capable of providing detailed information about the electronic structure of polarized solid-liquid interfaces [9]. Ex-situ s tu di es a r e u n ab l e to d e s c ri b e s u ch complex electrochemical processes since the chemical reactions are often rather unique and cannot be "quenched" and investigated by "post-mortem" studies [10]. X-ray spectroscopy is a powerful element specific technique that allows for an unequivocal assignm...

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