Zinc-Cobalt Alloy Deposited on the Titanium Surface as Electrocatalysts for Borohydride Oxidation

The present work is focused on the investigation of the electrochemical oxidation of borohydride in alkaline solution on low-cost ZnCo alloy deposited on the titanium surface (denoted as ZnCo/Ti). The ZnCo alloy coatings with the thickness of ~5 µm were deposited on the titanium surface (1 x1 cm) via electrodeposition from the electrolyte described in Ref. [1]. Prior to ZnCo alloy deposition, the titanium plates were degreased with acetone and then pretreated in diluted H₂SO₄ (1:1 vol) at 90 ^oC for 10 s. Cobalt coatings with the thickness of ~3 µm were deposited from the same electrolyte [1] with only difference that zinc ions were excluded from the plating bath.

The morphology, structure and composition of the prepared catalysts were examined by FESEM, EDS and ICP-OES. Activity of the fabricated catalysts was investigated towards the oxidation of borohydride by means of cyclic voltammetry and chronoamperometry.

It was found that the ZnCo alloy coating, electrodeposited on the titanium surface, consists of ~81.3 at. % of Zn and ~16.1 at. % of Co.

It has been determined that the Co/Ti and ZnCo/Ti catalysts catalyzes oxidation of H₂ generated by catalytic hydrolysis of BH₄^– and direct BH₄^– ions oxidation. Notably, the H₂ oxidation current densities measured on both catalysts are similar and reach up to 60 mA cm^–2, whereas, the borohydride oxidation current densities are ~3-6 times higher on the ZnCo/Ti catalysts than those obtained on the Co/Ti catalyst. The chronoamperometry and chronopotentiometry studies also confirmed a high electrocatalytic activity of the ZnCo/Ti catalyst for the direct electro-oxidation of BH₄^– ions as compared to that of Co/Ti electrode.

The ZnCo/Ti catalysts are promising low-cost anode material for direct borohydride fuel cells.

References

[1] E. Juzeliûnas, S. Lichušina. Patent of the Republic of Lithuania No. 5481 26.03.2008.