Oxyphilic tungsten single-atom-boosted oxygen reduction on palladium-based catalysts

Palladium (Pd) is regarded as one of the best catalysts for alkaline oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). Nevertheless, oxygen adsorption on Pd is slightly strong and awaits rational modulation strategies. It is challenging to modify the adsorption of oxygen intermediates based on precise control over surface structure. Herein, using Pd x W as model catalyst, the first-principles calculations reveal that a rational control of the range of oxyphilic metal W content is crucial for oxygen adsorption. Hence a series of Pd x W catalysts with tunable W content are synthesized. Their ORR activities display a volcano-shaped dependence on the content of W. The Pd 48 W/C catalyst, with single-atomic W atoms at the near-surface confirmed by X-ray absorption spectrum, exhibits the optimal performance with a mass activity of 2.28 A/mg Pd at 0.9 V (vs. RHE) in an alkaline electrolyte and membrane electrode assembly. In situ ATR-SEIRAS and density functional theory (DFT) calculations reveal that the enhanced ORR performance stems from weaker *OH adsorption and stronger *OOH adsorption, whereby the scaling relation of the oxygen intermediates is decoupled. This work demonstrates a strategy of designing high-performance Pd-based ORR catalyst with early-transition metals for AEMFC.