Promotion of PtIr and Pt catalytic activity towards ammonia electrooxidation through the modification of Zn

- Zn was introduced into PtIr and Pt through electro-deposition and dissolution.
- Introducing Zn into PtIr and Pt promotes ammonia electrooxidation reaction.
- PtIrZn demonstrates an onset potential of 0.30 V vs RHE.
- The onset potential of 0.30 V is the lowest value reported so far.
- Exchange current density of ammonia oxidation on PtIrZn exceeds 4 × 10− 8 A cm− 2.

Zn is introduced into Pt and PtIr electrodes by applying potential cycles to their corresponding polycrystalline microdisc electrodes in a ZnCl2-containing ionic liquid bath. Scanning-electron microscopy and energy-dispersive X-ray microanalysis studies show that nanostructured PtIrZn and PtZn layers created on the microdisc electrodes contain approximately 5 wt% Zn. Cyclic voltammetric studies reveal that PtZn and PtIrZn are significantly more active towards electrochemical ammonia oxidation in alkaline media than virgin Pt and PtIr electrodes. The PtIrZn electrode demonstrates a low onset potential of 0.30 V vs RHE and a high exchange current density of 4.3 × 10− 8 A cm− 2, which is favorably comparable to state-of-the-art electrocatalyts for the same reaction. The catalytic activity promotion by the Zn modification may be related to the inhibition of the hydrogen electrochemistry. PtIrZn appears therefore to be a very promising anode catalyst for direct ammonia fuel cells and ammonia electrolysis.

Introduction of Zn into PtIr alloy efficiently decreases the onset potential of ammonia oxidation reaction in alkaline media by approximately 100 mV.226