# 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
### Alternative Carbon Supports  
High surface area carbon materials (>1000 m\({}^{2}\) g\({}^{-1}\)) such as carbon nanotubes (CNTs) are used to improve the metal dispersion further. CNTs are nanostructured hexagonal rings and members of the fullerene family. They are formed from planar crystalline graphene sheets. CNTs are distinguished from other forms of carbon nanomaterials by their cylindrical shape. Because of their wide pore distribution, excellent chemical stability and surface area, good aspect ratio, and electrical conductivity, CNTs are regarded as the most commonly used catalyst support in fuel cells [24; 25; 47]. Metal particles deposited on CNT would be advantageous for a wide range of electro-catalytic applications. Despite their widespread use, CNTs are hydrophobic in nature that allows poor adsorption of catalyst precursors and catalysts. To get effective metal dispersion on support, surface modification without alteration in the properties of CNTs is essential. Therefore, they are subjected to functionalization treatment, through which oxygen-containing functional groups such as carbonyl (-C=O), hydroxyl (-OH), carboxyl (-COOH) are created on the CNTs surface so as to make it hydrophilic [48]. Surface modification of CNTs by functionalization (chemical/electrochemical) is essential for the control of noble metal nanoparticle size and dispersion without aggregation [49; 50]. [PERSON] et al. [51] reported the synthesis of uniform Pt nanoclusters on the functionalized single walled nanotubes (SWCNTs) electrode using the pulse electrodeposition technique. For comparison, deposition was also carried out on the functionalized Vulcan carbon electrode. SEM images showed that the Pt/Vulcan exhibited long leaf-like nano clusters with a diameter of 200-300 nm. The Pt nanoclusters deposited on SWCNTs exhibited a flower-like morphology and were composed of leaf-like substructures of length \(\sim\)40 nm and diameter of 100-200 nm with a better dispersion than that of Pt/Vulcan. The results showed that changing the support material from Vulcan to SWCNTs influenced the nucleation and growth, size, morphology, and dispersion of the deposited Pt. Electrochemical results showed that Pt/SWCNTs displayed larger electrochemical surface areas, enhanced activities, and stabilities towards methanol oxidation and oxygen reduction than that of Pt/Vulcan. RDE results showed that ORR kinetics on Pt/SWCNTs followed a 4-electron pathway. The authors explained that the substructures of the Pt nanocluster, along with the unique structural and electrical properties, were the responsible factors for its enhancement in activity towards the methanol oxidation and ORR over that of Pt/Vulcan. [PERSON] et al. [52] developed a novel three-step electrochemical method to deposit Pt-Ru-Ni alloy nanoparticle clusters on multi-walled carbon nanotubes (MWCNTs) and investigated the electrocatalytic methanol oxidation reaction. Figure 3 represents the schematic of the step-wise synthesis of Pt-Ru-Ni catalysts via electrodeposition on electrochemically activated MWCNTs. The authors attributed the enhanced activity towards the electrocatalytic activity of methanol oxidation reaction to the improved CO tolerance, synergetic effect of bifunctional catalysts, and presence of oxygen functional groups on the electrochemically activated MWCNTs surface. Significant attention has been paid to the synthesis of CNTs based nanocomposites as support material for a considerable time because of their excellent chemical stability and electrical property. Moreover, other physiochemical and thermal properties of nanocomposites such as high specific surface area, dimensional stability were contributed by the CNTs and other high surface carbon support materials. Many reports [16,53] presented a general overview of the electrode structures, recently developed materials, with an emphasis on the application of catalyst supported on various carbon supports in DLFCs.