# Progress in the Development of Electrodeposited Catalysts for Direct Liquid Fuel Cell Applications
## 4 Shape Control--A Way Forward
#### Deep Eutectic Solvents--A Versatile Approach
The superior capability of Pt nanoflowers with sharp petals to break the C-C bond along with the oxidation of adsorbed CO was found to be responsible for the exceptional activities towards ethanol oxidation. The same group [111] devised a simple electrodeposition route to achieve Pd polyhedral shaped nanocrystals with various sizes, including cubes, truncated cubes, cuboctahedrons, truncated octahedrons, and octahedrons with controlled size and shape. Pd nanocubes were initially synthesized from deep eutectic solvent ChCl:Urea by applying the square wave potential technique and controlling the Pd precursor concentration in the range 1 mM to 5 mM, obtained well-controlled polyhedral nanocrystals with different intensity ratios of [100] to [111] Pd facets on the surface. ChCl:Urea as a DES was observed to be critical in the development of different Pd polyhedral shaped crystals. Square wave potential technique was shown to favour the control of [111]/[100] facets. Pd truncated cubes with an optimum [111]/[100] facet ratio were identified to be the best one for formic acid oxidation, underlining the surface structure sensitive nature of the developed Pd polyhedrons. Their research highlighted the importance of rationale design and effective control over size and shape of the metal particles/crystallites for improving the performance in the electro-catalytic oxidation of formic acid. Table 5 provides a summary of the shape-controlled Pt and Pd catalysts that are obtained via electrodeposition employing ILs and DESs. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Fuel Cell Reaction** & **Catalyst** & **Technique** & **Electrolyte** & **Morphology** & **Dominant** & **Crystal Size,** & **Reference** \\  & **Studied** & **Pt** & PS 2 & \begin{tabular}{c} H\({}_{2}\)PtCl\({}_{6}\) + \\ [BMm][BF\({}_{4}\)] \\ \end{tabular} & nanoclusters & - & \textless{}100 & [108] \\ \hline MeOH Oxidation & Pt & PS & \begin{tabular}{c} H\({}_{2}\)PtCl\({}_{6}\) + \\ [BMm][FF\({}_{6}\)] \\ \end{tabular} & nanoclusters & - & \textless{}100 & [108] \\ \hline EtOH 1 Oxidation & Pt & SWP & \begin{tabular}{c} 19.3 mM H\({}_{2}\)PtCl\({}_{6}\) + \\ [ChCl:Urea--1:2] \\ \end{tabular} & \begin{tabular}{c} Concave tetra \\ hexahedral \\ \end{tabular} & [910] & 167.5 & [110] \\ \hline HCOOH 1 Oxidation & Pd & SWP 2 & \begin{tabular}{c} 1 mM PdCl\({}_{2}\) + \\ [ChCl:Urea--1:2] \\ \end{tabular} & Cube & [100] & - & [111] \\ \hline HCOOH Oxidation & Pd & SWP & \begin{tabular}{c} 2 mM PdCl\({}_{2}\) + \\ [ChCl:Urea--1:2] \\ \end{tabular} & Truncated cube & [100] & & [111] \\ \hline HCOOH Oxidation & Pd & SWP & \begin{tabular}{c} 3 mM PdCl\({}_{2}\) + \\ [ChCl:Urea--1:2] \\ \end{tabular} & Octahedron & [100], [111] & & [111] \\ \hline HCOOH Oxidation & Pd & SWP & \begin{tabular}{c} 4 mM PdCl\({}_{2}\) + \\ [ChCl:Urea--1:2] \\ \end{tabular} & Truncated & [100], [111] & & [111] \\ \hline HCOOH Oxidation & Pd & SWP & \begin{tabular}{c} 5 mM PdCl\({}_{2}\) + \\ [ChCl:Urea--1:2] \\ \end{tabular} & Octahedron & [111] & & [111] \\ \hline EtOH Oxidation & Pt & CV 2 & \begin{tabular}{c} 19.3 mM H\({}_{2}\)PtCl\({}_{6}\) + \\ [ChCl:Urea--1:2] \\ \end{tabular} & Nanoflowers & [111] & 200 & [112] \\ \hline EtOH Oxidation & Pt & SWP & \
\begin{tabular}{c} 19.3 mM H\({}_{2}\)PtCl\({}_{6}\) + \\ [ChCl:Urea--1:2] \\ \end{tabular} & Triambic & [771] & 100 & [113] \\ \hline - & Pd & CV &
\begin{tabular}{c} 10 mM K\({}_{2}\)PdCl\({}_{4}\) + \\ [ChCl:Urea--1:2] \\ \end{tabular} & Nanoparticles & - & 20 & [114] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of the shape-controlled Pt and Pd catalysts that are obtained via electrodeposition employing ionic liquids and deep eutectic solvents. As can be seen from the table, it is clearly indicated that the DESs could be potential viable alternative electrolytes in obtaining shape-controlled Pt and Pd based catalysts. On the one hand, the wide electrochemical window allows deposition at high potentials and offers an advantage to maintain the stability of the electrolyte.