Tuning d-band centers by coupling PdO nanoclusters to WO3 nanosheets to promote the oxygen reduction reaction

Abstract

Supporting Pd on a metal oxide is an effective way to modulate its electronic structure to enhance its electrocatalytic activity in the oxygen reduction reaction (ORR). However, strong coupling between Pd and metal oxides typically requires high-temperature synthesis or annealing. Here, we report a mild and effective approach for synthesis of PdO nanoclusters coupled to WO₃ nanosheets (PdO@WO₃S_x) via direct conversion of metallic 1T-WS₂ nanosheets into WO₃ by spontaneous deposition of PdO onto the nanosheets in H₂O at 50 °C for 1 h. Strong coupling in as-prepared PdO@WO₃S_x was confirmed by observing shifts in binding energy compared to those of pure PdO and WO₃. 1T-MoS₂ nanosheets were partially converted into MoO₃ in an analogous reaction to produce the hybrid MoS_xO₃ but in low yield due to preferential dissolution forming aqueous MoO₄²⁻. The hybrid PdO@WO₃S_x exhibited higher half-wave potential (0.89 V vs. RHE) and limiting current density (−6.24 mA cm⁻²) in the ORR than both PdO@MoS_xO₃ and commercial Pt/C. In addition to its higher electrocatalytic activity, PdO@WO₃S_x showed greater durability compared to Pt/C in the electrocatalytic activity during the continuous ORR. Computational simulations based on d-band center theory reveal that the d-band center of Pd in PdO@WO₃S_x was upshifted to −2.57 eV, very close to that of Pt. This Pt-like d-band center of PdO@WO₃S_x enabled its excellent electrocatalytic activity in the ORR. This work presents a facile approach to the synthesis of PdO hybrid catalysts and provides fundamental insight into their enhanced electrocatalytic activity for the ORR.