Exploration of Reverse Micelle Synthesis of Carbon-Supported LaMnO[sub 3]

Abstract

Reverse micelle ͑RM͒ based synthesis of carbon-supported perovskite type oxide (LaMnO 3 ) was investigated. By using cyclohexane as oil phase, six kinds of nonionic surfactants were tested for the formation of the revere micelle dispersions containing aqueous solutions of mixed nitrates of La 3ϩ and Mn 2ϩ ͑RM-N͒ and tetramethylammonium hydroxide ͑RM-A͒ at the water/ surfactant molar ratio (R w ) of 3. RM-A was found to be more difficult to form compared with RM-N or the RM containing pure water. At a temperature range of 5-25°C, it was given only by the surfactants with hydrophilic-lipophilic balance ͑HLB͒ values of 10.0-10.9. Phase diagrams of oil-surfactant-alkaline solution ͑or pure water͒ were constructed at 5 and 15°C for the best two surfactants, i.e., poly-(oxyetylene) 6 -nonylphenyl ether and poly-(oxyetylene) 5 -lauryl ether. Mixing RM-N and RM-A together gave the RM containing a mixed hydroxides-precursor ͑RM-P͒, which was further converted into carbon-supported LaMnO 3 through a series of treatments including the addition of carbon powder and calcination in N 2 atmosphere at 600°C. The size of RM-P as well as that of the LaMnO 3 grains supported on carbon could be controlled well by selecting R w . The carbon-supported LaMnO 3 proved to be highly active for the electrochemical reduction of oxygen.

Structural optimization of gas diffusion electrodes loaded with LaMnO3 electrocatalysts

“…The obtained hydroxide deposited on the carbon black was calcined under a nitrogen flow to form the perovskite-type oxide. By using La 1-x Sr x Mn 1-y Fe y O 3 -loaded carbon electrodes, fabricated through the RM method, we achieved relatively small overpotentials for oxygen reduction [32], which are similar to those for Pt-loaded carbon electrodes.…”

“…Figure 2 shows the preparation procedure for LaMnO 3 -loaded carbon black using an RM method. By adopting the RM method, nano-sized LaMnO 3 can be finely loaded onto carbon matrices as previously reported [28][29][30]. Initially, two reverse micelle solutions, denoted as RM-A and RM-B, were prepared, respectively, by adding aqueous solutions containing La and Mn nitrates (0.2 mol l -1 ) and tetramethylammonium hydroxide (TMAH; 10 wt%) separately into organic solutions containing cyclohexane and nonionic surfactant (hexaethylene glycol nonylphenyl ether; NP-6).…”

“…It is well known that the high dispersion of electrocatalysts with high surface areas onto carbon supports usually leads to an increase in the electrocatalytic activity. Hence, to achieve homogeneous deposition of perovskite oxides on carbon supports and thus to give high electrocatalytic activity, we focused on a reverse micelle (RM) method for the fabrication of a catalyst layer for GDEs [27][28][29][30][31]. In this method, nano-sized precursor hydroxides are prepared inside nano-sized water droplets (reverse micelles), surrounded by surfactants, in an organic solvent.…”

Synthesis of nano-particle and highly porous conducting perovskites from simple in situ sol-gel derived carbon templating process

“…Complicated reverse Micelle method, reverse homogeneous precipitation method, or catalytic hydrocarbon dissociation reaction method has been successfully reported for the synthesis of carbon-perovskite composite (Hayashi et al 1998;Imaizumi et al 2004;Yuasa et al 2004). In those methods, either the perovskite or the carbon was pre-formed before mixing.…”

“…Porous cathode built up from nano particles then has the advantage of high surface area and so low activation polarization (Zhang et al 2005). Furthermore, the support of perovskite over carbon, or the formation of carbon-perovskite mixture can substantially increase the dispersion of electrocatalyst, noticeable increase in the electrode performance of metal-air battery was observed due to the increase in effective surface area of electrocatalyst with the help of dispersion (Hayashi et al 1998;Weidenkaff et al 2002;Yuasa et al 2004;Imaizumi et al 2004).…”