Zaenal Awaludin

An XPS depth-profile study on electrochemically deposited TaO x

Through the use of XPS and controlled Ar+ etching, the surface composition and oxide species of tantalum oxides (TaOx), which were electrodeposited on glassy carbon electrodes by cyclic voltammetric and constant-potential electrolyses, are quantified along the depth profile. Electrodeposition exhibits efficacy in depositing TaOx with a distribution of various TaOx: TaO, TaO2, and Ta2O5. The distribution gradient from the outer surface of TaOx is such that Ta2O5 > TaO2 > TaO. TaO is found to be the dominant species in the underlying layer of TaOx. Such a unique structure of the electrode surface is analogous to that of nanoparticles with a core–shell structure, with the core being suboxides and the surface being that of the saturated pentoxide, Ta2O5. The electrochemically induced nonhydrolytic condensation route is proposed to be capable of producing TaOx with a distribution gradient of Ta2O5, TaO2, and TaO in the depth direction.

TaOx-capped Pt nanoparticles as active and durable electrocatalysts for oxygen reduction

Here we demonstrate the formation of unique structure of TaOx-capped Pt nanoparticles on a Pt/TaOx/GC electrocatalyst, where at first tantalum oxide (TaOx) and next Pt nanoparticles were electrodeposited on the glassy carbon (GC) substrate, for an oxygen reduction reaction. The surface characterizations show that the nanoparticles of TaOx deposit homogeneously on the GC surface, forming a thin layer and surprisingly, the Pt nanoparticles do not exactly deposit on the top layer of the TaOx, i.e., Ta2O5 but inside their framework and consequently a unique assembly of the TaOx-capped Pt particles is fabricated. The analyses using XPS spectra indicate electronic interactions of TaOx with the GC, as well as with the Pt nanoparticles. The electrochemical measurements conducted by cyclic voltammetry and rotating ring-disk electrode voltammetry reveal that the novel electrocatalyst possesses an enhanced activity for an oxygen reduction reaction, without any loss of performance even after 250 000 cycles (1111 h) of a durability test. The plausible reasons for the remarkable activity and durability of this electrocatalyst are proposed.

Investigating the physical and electrochemical effects of cathodic polarization treatment on TaOx

In the development of non-noble metal electrocatalysts, tantalum oxide (TaOx)-based materials possess promising potential due to their high corrosion resistance. In the stoichiometric and bulk form, however, the oxide is extremely inactive. Here, we explored the effects of electrochemical reduction treatment on the physical and electrochemical properties of TaOx. The oxide was electrochemically deposited on a glassy carbon electrode. The treatment employed a cyclic voltammetry technique in sulfuric acid solution and required no heat treatment. The X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the stoichiometric Ta2O5 is reduced generating the oxides with a predominant oxidation state of 4+. Remarkably, the electrochemically reduced TaOx showed high activity in hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). These findings suggest that the electrochemically reductive treatment is an effective way to activate TaOx for the electrocatalytic reactions which could be originated from the suboxide species, i.e., Ta4+.