Theoretical insights into electronic structures and durability of single-atom Pd/TiN catalysts

Density functional theory (DFT) calculations have been performed to evaluate the metal-support interactions between palladium atom and titanium nitride surface (Pd–TiN). N vacancy sites on defective TiN surface can stabilize Pd single atom under strongly oxidizing conditions, and surface defect-mediated stabilization is accompanied by obvious charge redistributions between Pd and substrate. The adsorption of several gas species on stable Pd–TiN surfaces is also explored to understand catalytic reactions. It is found that O, H, OH, O2, and CO favorably adsorb on Ti atop site, while CO2 and H2 prefer the hollow and Pd atop site, respectively. Moreover, co-adsorption with either H or OH weakens the CO-surface interactions, indicating the CO poisoning effect would be alleviated under both acidic and alkaline conditions. This study provides a perspective to understand the support effect of Pd–TiN, which sheds light on the design of high-performance Pd-based electrodes for proton exchange membrane fuel cells (PEMFCs).