• Palladium is a catalyst used in variety of reactions involving electro-oxidation and reduction.
• Solid polymer electrolyte (SPE) reactors are made of palladium catalysts and allow facile transport of ionic species to the catalyst surface through the membrane  under an applied potential.
• However, the control over morphology of palladium nanostructures on carbon or CNTs based substrates has been difficult, especially with the conventional  method of the chemical reduction.

Hence, there is a demand of a new method to address  the above mentioned issues.

A method of preparing palladium dendrites

a) Coating carbon nano-tubes (CNTs) on a graphite substrate

b) Activating the substrate electrochemically

c) Electrodepositing palladium on the activated substrate

wherein steps a) to c) are carried out without  using a template, surfactant and/or additive.

• The morphology of the palladium particles from spherical to dendritic structure is tailored by controlling the deposition potential on  electrochemically activated CNTs substrate.
• The dendritic nanostructures is grown by increasing the precursor concentration at an appropriate deposition potential.
• The preparation of palladium dendrites is done at room temperature and atmospheric pressure.
• The CNT is coated as a thin layer on a graphite substrate (graphite electrode) by dispersing CNTs in a mixture of an ionomer (Nafion®) and solvent  (isopropanol), followed by blending ultrasonically.
• CNT loading on the graphite substrate is about 100 μg cm-2 and coated graphite is air dried.
• The CNT coated graphite substrate is activated electrochemically by potential cycling (100 cycles) in acidic electrolyte (sulfuric acid with  0.5M strength) that helps to improve hydrophilicity  & generates CNT surface defects.
• Platinum wire and Ag/AgCl (3M NaCl) is used as counter & reference electrodes, respectively.
• The potential range is -0.2 to 1.1 V vs. Ag/AgCl and scan rate is 100 mV s-1.
• Palladium is deposited by constant potential technique and the deposition potential and precursor concentration are modified to increase  the dendritic morphology.

Fig. 1 provides scanning electron micrographs of  electrodeposited Pd on electrochemically activated  CNT coated substrate at

a) 2 V, b) 0.3 V, c) 0.4 V and d) 0.5 V.

Fig. 2 provides scanning electron micrographs of  electrodeposited Pd on electrochemically activated  CNT coated substrate at 0.2 V with varying  precursor concentrations:

(a) 1 mM, (b) 1.5 mM and (c) 2 mM.

Wherein, CNTs were electrochemical activation in nitrogen saturated 0.5 M H2SO4 prior to deposition.