# Progress in the Development of Electrodeposited Catalysts for Direct Liquid Fuel Cell Applications
## 2 Progress in the Electrodeposition of Carbon Supported Pt and Pd Catalysts
### Electrodeposition of Pt  
Electrochemical deposition of precious metals is a method that involves the reduction of the desired metal ions from solution to the metallic state on the surface of a substrate in aqueous electrolytes [27]. [PERSON] et al. [28] carried out the electrooxidation of methanol utilising Pt nanoparticles onto porous carbon substrates obtained by potential step electrodeposition experiments. The purpose of the work was to determine the characteristics of Pt electrodeposited on various carbon supports, viz., graphite powder and conventional carbon, mixed with recast Nafion. Besides the effect of surface oxides, the influence of Pt specific surface area on methanol oxidation at various carbon supported Pt/recast Nafion was investigated. The experimental results obtained in this work for the methanol oxidation suggested that the Pt activity is more likely related to the fine Pt surface structures but not to the particle size. The fine structure, in turn, might be influenced by the Pt specific surface area, the nature of substrate, or the preparation procedure of the catalyst. In general, electrocatalysts synthesized by wet-chemical synthesis can be deposited at the membrane-electrode interface in two different ways: (i) direct coating of catalyst onto the membrane and (ii) application of catalyst ink on the carbon substrate (carbon paper/carbon cloth). Direct application on the solid membrane creates a thin electrocataly layer resulting in a low catalyst loading and good mass transport properties. In contrast, the application of catalyst ink on the substrate may require a higher catalyst loading since the catalyst ink tends to penetrate into the substrate, resulting in inactive sites where no ionic contact is established [29]. When the catalyst loading is lowered, maintaining or improving catalyst performance towards fuel cell reactions becomes extremely challenging. In order to achieve this, several efforts were devoted towards the utilization of Pt and the enhancement of catalyst activity [30]. The specific surface area of a metal catalyst will determine the utilization efficiency of metal towards a particular fuel cell reaction. Improving the noble metal particle utilization will extend the three-phase boundary (a region where reactant, catalyst, and electrolyte are in contact), which in turn increases the specific surface area of the metal catalyst. Efforts to decrease Pt loading through increased Pt utilization have resulted in the development of several novel methods. These can be broadly categorized into two groups: one is to use new materials to construct the catalyst layer, and the other is to optimize the structure of the catalyst layer, increase its utility and minimize irreversible losses. The former can be accomplished by modification of supported Pt. The latter is achieved by optimizing the structure of the catalyst layer using different fabrication methods and materials. The effective utilization of Pt nanoparticles towards the electrochemical reactions is strongly dependant on the contact between the membrane (PEM) and the noble metal Pt, i.e., on the thickness of the catalyst layer. Increasing the thickness of the catalyst layer will reduce the utilization efficiency of the catalyst. In general, the thickness of the catalyst layer depends on the nature of the carbon-coated substrates, i.e., on the hydrophobic/hydrophilic nature. If the nature of the substrate is hydrophilic, then the electrolyte would penetrate more deeply, resulting in the formation of a thick layer. On the other hand, the deposition would occur within a very narrow layer in the case of hydrophobic carbon substrates. To overcome this problem, [PERSON] et al. [31] developed a novel method to control the thickness of the catalyst layer. A hydrophobic layer of carbon ink, prepared by mixing pretreated Vulcan and isopropanol in a supersonic mixer, was coated on the carbon cloth. Glycerol was added to the above mixture and sprayed on the hydrophobic layer.