Inhibition of Nitrogen Poisoning on Pt during Ammonia Oxidation through Early Transition Metal Oxide Supports

We studied the effect of using early transition metal oxides (TiO₂, WO₃, Cr₂O₃), carbon nanotubes (CNT), and hexagonal boron nitride (BN) as a support on the electrochemical ammonia oxidation activity of Pt. Platinum deposits were formed on the support surface through chemical reduction. Voltammetric studies showed that the Pt supported on the transition metal oxide surface led to a significant enhancement in the ammonia oxidation reaction (AOR) activity with a current decay rate almost three times slower for the Pt/TiO₂ sample compared to the Pt/CNT sample. XPS analysis revealed a strong correlation between the downshift in the d-band center of these Pt/support samples and their current decay rates. The amount of adsorbed N species detected on the Pt/support surface was also found to decrease with slower decay rates. We also tested the Pt/CNT and Pt/TiO₂ samples in a membrane electrode assembly (MEA) using an alternating potential method to carry out long-term ammonia electrolysis. The Pt/TiO₂ catalyst lasted for 12 h over a current density above 40 mA/mg_Pt, significantly longer compared to the Pt/CNT catalyst that only lasted for 4 h over a course of 100 potential cycles in the MEA. This study shows that the AOR intermediate energies can be tuned using metal support interactions from transition metal oxide supports and also provides guidance for the operation of efficient MEA ammonia electrolyzers.