Transition Metal Oxides as DMFC Cathodes Without Platinum

Abstract

Transition metal oxides ͑ZrO 2 , TiO 2 , SnO 2 , Nb 2 O 5 , and Co 3 O 4 ͒ made by sputtering methods were investigated as new electrocatalysts for the cathode of a direct methanol fuel cell ͑DMFC͒ without platinum. The catalytic activity for the oxygen reduction of these transition metal oxides was evaluated in sulfuric acid with and without 0.1 M methanol. The sputtered metal oxides had stable states in acid medium at least in the potential range of the oxygen reduction. The metal oxides were not active for the methanol oxidation. The oxygen reduction activity of the metal oxides decreased in the following order: ZrOin the presence of methanol. Zirconium oxides showed the best activity for the oxygen reduction among these transition metal oxides. Moreover, in comparison with the sputtered Pt, the potential at i O 2 -N 2 = −5 A cm −2 of ZrO 2−x was 60 mV larger than that of the sputtered Pt. This is due to the high selectivity of the metal oxides for the oxygen reduction. The mixed potential as found on the Pt electrode was not observed on the metal oxide catalysts. Zirconium oxides could be a good cathode substituting the platinum cathode for DMFCs.

Electrochemical and physicochemical properties of titanium Oxy-nitride electrocatalyst prepared by sol-gel methods for the oxygen reduction reaction purposes

“…Therefore, reporting the final concentration of a metal ion, for instance, without giving information about its initial quantity cannot help one to evaluate the sample's chemical stability. For example, it has been reported that the average Ti concentration after 24 days at 50°C in 0.1 mol/dm 3 sulfuric acid under atmospheric conditions is about 3.5 × 10 −7 ml/dm 3 [36]. Therefore, in the present work, the ICP-ToF-MS results are referred to the initial mass of the electrocatalyst in terms of percentage.…”

“…In particular, titanium oxide is interesting owing to its abundant natural resources. It has been found that the catalytic activity of titanium oxide for the ORR might be affected by changing the surface state, crystalline structure, and the work function [36]. Since an oxygen molecule hardly adsorbs on a surface of perfect oxides, such as TiO 2 , it is essential to create some defects in the oxygen adsorption sites on the catalyst surface while the metal is basically kept at the highest oxidation state [37,35].…”

Platinfreie Nanomaterialien für die Sauerstoffreduktion

“…[99,100] Andere Metalloxide wie etwa Fe-, Cu-, Ti-, Zr-, Ta-, Nb-und Sn-basierte Oxide wurden ebenfalls als neue ORR-Elektrokatalysatoren untersucht. [101][102][103][104][105][106][107][108][109][110] Diese zeigen jedoch leider geringere Aktivitäten als die Co-oder Mn-basierten Oxide.…”

Novel, Highly Conductive Pt/TiO2 Thin‐Film Model Catalyst Electrodes: The Role of Metal–Support Interactions

“…So far, thin metal oxide films have been prepared via different methods, including the deposition of an oxide ink onto a conductive substrate followed by drying or even calcination, [9] chemical vapor deposition (CVD), [15] spray coating [16] or by reactive sputtering of Ti in an O2 atmosphere. [17] In the first case, it is hard to control the film, the latter three methods suffer from other problems such as deviations in the film stoichiometry, which may strongly affect the electronic properties and consequently also the electrocatalytic properties of the resulting films, as shown, e.g., by Liu et al for the oxygen reduction reaction (ORR) on several metal oxides. [17;18] In this work we used electrodeposition of TiO2 on a conducting substrate such as glassy carbon or indium doped tin oxide (ITO), to fabricate TiO2 films of controlled thickness, in the range of about 100 nm (for details see section 3.1 and ref.…”