# Progress in the Development of Electrodeposited Catalysts for Direct Liquid Fuel Cell Applications
## 4 Shape Control--A Way Forward
The insertion of such defects on the carbon surface favoured a good deposition, resulting in dendritic morphology with dominant [111] facets, which facilitated the better performance of fuel cell reactions such as ORR, formic acid oxidation in low temperature (direct methanol and formic acid) fuel cells. The results showed that tailoring the insertion of defects on the carbon according to their morphological nature (planar, tubular) will influence the shape and structure of metal deposited. Moreover, the development of Pd structures on substrates coated with different carbon supports (graphene, wood apple carbon, carbon nanotubes, Vulcan) and varying morphologies (such as planar, microspheres, tubular, mesoporous, etc. ), displayed 3-4-fold increase in electrocatalytic activity in comparison to conventional Pd deposit. Prior technologies were limited to the deposition of noble metals on carbon black support with defects, which favoured deposition with'spherical' morphology. For instance, Pt deposits on electrochemically activated carbon support developed by [PERSON] et al. [100] resulted in spherical morphology in contrast to the dendritic morphology obtained with Pd deposits. Figure 6 shows the influence of electrochemical activation on tuning the morphology from spherical to dendritic and their performance towards electrochemical oxidation. Figures 7 and 8 show the schematic of the methodologies involving the morphology transition from spherical to dendritic, its development, and validation on other carbon supports. [PERSON] et al. [98] extended it further by performing Pt electrodeposition on carbon black-coated carbon paper under potentiostatic mode at three different applied potentials: 0.2 V, 0 V, and \(-\)0.2 V vs. SHE. Microscopy results evidenced the morphological transformation of the electrodeposited Pt from globular (0.2 V) to dendritic (0 V) and rosette  
like (\(-0.2\) V) structure, signifying the influence of deposition potential on the morphological characteristics. Subsequently, approaches were developed towards controlling the metal agglomerations that were formed at different conditions. For instance, Pd deposited at 0.5 V (vs. RHE) and above on carbon supports resulted in the formation of irregular agglomerates. Controlling the agglomerates was accomplished either by tailoring the current or voltage [98] or by changing the catalyst support [101], or by altering the viscosity of the electrolyte by the addition of a suitable additive. For instance, in a work reported by [PERSON] and [PERSON] [102], a water soluble PEG was used as the additive, and the influence of PEG-6000 on the morphology of Pd deposited at 0.5 V (vs. RHE) was investigated. Physical characterisation data confirmed that the addition of PEG changed the Pd morphology from a spherical to a flower-like pattern, decreased the Pd intensity ratios between \(\{111\}/\{220\}\) and \(\{200\}/\{220\}\) planes, favoured the growth in a specific crystallographic direction with increase in PEG concentration up to 0.2 mM. Electrochemical tests evidenced a 3-4 times enhancement towards ORR, formic acid oxidation, achieved at the expense of reduced catalyst loading. For instance, at 50% catalyst loading, Pd nanoflowers demonstrated a 3-4-fold increase in electrochemical surface area, activity relative to spherical deposit (83.4 m\({}^{2}\) g\({}^{-1}\) vs. 25.1 m\({}^{2}\) g\({}^{-1}\)). Figure 6: Scanning electron micrographs of Pd on (**a**) non-activated carbon support and (**b**) electrochemically activated carbon support. (**c**) Raman spectra of non-activated and electrochemically activated Vulcan coated on graphite electrode. Loading of Vulcan on graphite substrate: 100 \(\upmu\)g cm\({}^{-2}\). Number of electrochemical activation cycles: 100. (**d**) Cyclic voltammograms comparing the specific activity of Pd catalyst on non-activated carbon and electrochemically activated carbon in nitrogen saturated 0.5 M H\({}_{2}\)SO\({}_{4}\) and 1 M HCOOH at a scan rate of 20 mV s\({}^{-1}\) and room temperature. Reprinted with permission from [95].