the Growth of Hierarchal Shape Tin Used As Catalysts Support Towards a Binder Free Fuel Cell Anodes

A novel catalyst support utilizing electrodeposited tin was investigated for direct liquid fuel cells. These materials were prepared by electrodeposition of tetragonal metallic Sn on Toray® carbon paper or gold electrodes under non-equilibrium conditions. Hierarchical shape branched dendrites of Sn were formed under selected experimental conditions (fig 1).  The growth process on these electrodes were rigorously investigated using potentiostatic or galvanostatic steps, in aqueous solutions containing sodium citrate, SDS, HTAB. Hydrogen evolution and mass balance calculations suggest that the columbic efficiency of Sn²⁺reduction is controlled by diffusion of the surfactant solvated ions.

Various morphologies of metallic Sn can be prepared by controlling the applied potential, duty cycle and the HCl additive. Hierarchal morphologies of Sn start to appear at an over potentials of more than 0.9V and is strongly influenced by hydrogen evolution competing reaction.

Characterization of the deposition the deposition and etching, passivation and activation processes were performed by EQCM. These results show that H₂SO₄ and HClO₄, which were applied in the activation of SnO₂ layer, prior to applying the catalyst, behave differently with the deposited metal. HClO₄seems to prevent further acting of the oxide layer and provide the required functionality for metal deposition as well as good passivation required stable operation as anodes. 

Pt, PtSn and Ni catalysts were loaded on electrodeposited Sn supported on Toray® carbon paper by electroless or by electroplating processes. These binder free anodes were measured in methanol, methyl- formate acid solutions, and nickel-plated was applied in urea oxidation in alkaline solutions. Superior oxidation specific activity was observed on all Sn supported anodes with respect to Pt or Ni catalysts loaded on carbon XC72.

Figure 1. HRSEM of electrodeposited Sn in a “tree” like shape