Preparation of high loading Pt supported on carbon by on-site reduction

The fuel cell, as one of the efficient, pollution free power sources, is approaching the commercialization stage [1, 2] after more than 160 years development [3], though the applications remain largely for aerospace and military use at present. This is benefited from breakthroughs of key technologies and materials [2, 4]. Electrode catalysts are especially crucial to the low temperature fuel cells (proton exchange membrane fuel cell, PEMFC, and direct methanol fuel cell, DMFC), which dominate the fuel cell performance and the cost as well. Apart from the discovery of new catalysts, it is important to invent catalyst preparation techniques since this directly relates to the catalyst properties and the cost. It is well known that commercially available carbon supported catalysts (M/C, where M = precious metal or alloy, C = carbon) are prepared by chemical methods [5–11]. Multi-step procedures and long-time treatments were needed to prepare high metal loading (M > 40 w%) catalyst. Otherwise, large metal clusters easily formed (favorable metal cluster size is around 4 nm [12] used in fuel cells). Another intrinsic problem is that the catalyst aggregates during the drying process when using conventional drying methods. The lumped catalyst should be re-broken by mechanical methods or ball milling to make fine powders. In that case, even the precious metal clusters attached on carbon were in nanometer scale, whereas the aggregated particle size would be in sub-micron scale. The utility of the catalyst dramatically reduced under such circumstances since catalytic reaction is a surface reaction. Highly dispersed (higher surface area) catalyst will provide higher activity. Several methods are now available for the preparation of carbon-supported catalysts [13–16]. The surfactant stabilized method and separate step absorption is an alternative to control small cluster size and make high precious metal loading [17]. However, the removal of surfactant added to the complexity. Therefore, the preparation of highly dispersed, nanometer sized catalysts remains a challenge. We report here a recently invented novel method that can avoid the weaknesses mentioned above. Simply regulating the procedure can control the size of Pt clusters. The advantages presently known and the experimental conditions are explained.