# 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
### Palladium--A Possible Alternative to Platinum  
DMFCs are regarded as one of the promising candidates among the low temperature DLFCs due to their relatively low fuel cost and high energy density. However, the fuel crossover through the Nafion membrane is considered to be the major obstacle affecting the performance of the DMFC despite the development of Pt-based bimetallic catalysts. In order to accelerate the cathodic reaction rate, Pd-based catalysts are identified as a potential alternative due to their reduced cost, properties similar to Pt. In addition, Pd-based catalysts exhibit superior methanol tolerance in acidic DMFCs with increased activity. Formic acid electrooxidation is an essential anodic reaction that has been shown to be much more active than Pt when catalysed by Pd. Prior studies revealed that the electrocatalytic oxidation of formic acid is structure sensitive, suggesting that it can be affected mainly by the facets exposed on the surface of a catalyst [22; 40; 42]. Considering the importance of Pd as an important noble metal, this section focuses on its utilization as a methanol tolerant ORR catalyst, electrocatalytic oxidation of formic acid, organic molecules [40; 43; 44; 45].  
[PERSON] et al. [46] reported fabrication of Pd catalyst on graphite rods employing different procedures: (i) direct electrodeposition (DE), (ii) direct electrodeposition with Nafion coating (DENC), (iii) repeated electrodeposition with Nafion coating (RENC), and (iv) dip coating (DC) and a schematic representation is shown in Figure 2.  
Graphite rods are considered as potential electrodes for microfluidic fuel cells due to their economic cost and inherent non-planar topologies. The graphite rods were initially pretreated to eliminate the surface oxides and impurities through a series of steps involving stirring in alkaline (1 M NaOH) and acidic (1 M HCl) media with an intermediate rinsing step followed by vacuum drying in an oven at 80 C, and Pd deposition employing the procedures shown in Figure 2. Microscopy characterisation results showed that the Pd catalysts synthesised by DE and DENC approach displayed a dendritic structure, but the ones prepared by RENC  
Figure 2: Schematic showing the procedure for fabricating the Pd catalyst on graphite rods through different routes: (**a**) Direct electrodeposition (DE), (**b**) Direct electrodeposition with Nafion coating (DENC), (**c**) Repeated electrodeposition with Nafion coating (RENC), and (**d**) Dip coating (DC) [46].  
approach resulted in an island structure. Electrostatic repulsion between the [PdCl\({}_{4}\)]\({}^{2-}\) anions during electrodeposition and the anionic sulfonic groups of the membrane (Nafion) was shown to influence the morphological characteristics, changing it from dendritic to island. Cross sectional images showed that the electrodes prepared by DE/DENC had similar morphology with the same thickness, while the RENC based electrodes showed a multi-layer structure, highlighting the novel approach associated with the latter.  
Electrochemical results showed superior formic acid oxidation performance, and durability of the RENC prepared Pd catalyst to the other fabrication methods. The multi-layer structure of the RENC electrode and the presence of active Pd [111] crystal facet was shown to produce a combined beneficial effect. It resulted in an increased electrochemical surface area with improved catalyst utilization, demonstrating the valuable features of RENC based approach.