The Effectiveness of Sputtered PtCo Catalysts on TiO[sub 2] Nanotube Arrays for the Oxygen Reduction Reaction

Abstract

Pt and PtCo binary catalyst layers were prepared on self-ordered TinormalO2 nanotube (TONT) arrays with the length of 1μm and diameter of 120nm employing a dual-gun sputtering method. The sputtered Pt induced a slight increase of the wall thickness of TONT. With increasing Co content in the alloy catalyst layer, a slight reduction of pore diameter on the TONT was also found. Well-dispersed mixed nanophases of Pt and Co were observed along the inner wall of TONT, and crystalline properties from the crystalline plane of Pt, Co, and TinormalO2 were identified by selective area electron diffraction. Among several compositions of additional Co on Pt, 30at% Co catalyst on Pt showed the best oxygen reduction reaction (ORR) activity with the positive shift (200mV) of onset potential. This is attributed to Pt electronic modification by an alloying effect and the shortening of the Pt–Pt interatomic distance. However, the coverage from the physically deposited sputtering method is incomplete; thus, the uniformity of the catalyst layer could be improved along the inner wall of TONT. Moreover, the influence of the pore size for diffusion of oxygen molecules on the ORR was investigated by increasing the sputtering time for normalPt70normalCo30∕TONT . The normalPt70normalCo30∕TONT sample with the pore diameter of 70nm (sputtering time of 180s ) showed the maximum ORR activity (maximum upshift of half-wave potential), while above that, the ORR activity started to be degraded, resulting from restricted diffusion of oxygen molecules and the reduced surface area of catalyst layer. In order to examine the effect on large surface area of TONT and pore diameter, a compact TinormalO2 film prepared on a Ti substrate was compared for the normalPt70normalCo30 catalyst layer. This compact TinormalO2 support revealed significantly degraded ORR activity.

Stability and Activity of Pt/ITO Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media

“…The role of peroxide-induced membrane degradation is well documented in both acid and alkaline media [4]. Among the state-of-the-art support materials, metal oxide supports as alternatives to carbon have generally shown improved corrosion resistance and reduced electrochemical surface area (ECSA) degradation rates [26][27][28][29][30][31][32]. Metal-support interactions can also improve the electrocatalytic activity of the supported Pt in several ways such as modification of the electronic states of Pt to increase the formation potential of Pt-OH groups [33] and reduction of the equilibrium OH adsorption by lateral repulsion between Pt-OH and oxide surface [34][35][36].…”

Electrochemical oxygen reduction behaviour of platinum nanoparticles supported on multi-walled carbon nanotube/titanium dioxide composites

“…Dual-gun sputtering technique was used for the preparation of TiO 2 nanotube arrays as carbon-free support for PtCo catalyst. Pt 70 Co 30 catalyst had the highest specific surface area and thus the maximum electrocatalytic activity for ORR in 0.5 M HClO 4 [56]. In our earlier work we employed the thermal decomposition method for the preparation of Pt-TiO 2 catalysts for oxygen reduction [57].…”

Metal Oxide‐Supported Platinum Overlayers as Proton‐Exchange Membrane Fuel Cell Cathodes

“…One of the possible solutions is nanostructuring of the support. Preliminary research efforts, have shown promising results, however, further tests need to be made, particularly under real operating conditions [28,29,30].…”