Tuning d-band centers by coupling PdO nanoclusters to WO₃nanosheets to promote the oxygen reduction reaction

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@WO3Sx) 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@WO3Sx 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 MoSxO3 but in low yield due to preferential dissolution forming aqueous MoO42-. The hybrid PdO@WO3Sx 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@MoSxO3 and commercial Pt/C. In addition to its higher electrocatalytic activity, PdO@WO3Sx 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@WO3Sx was upshifted to -2.57 eV, very close to that of Pt. This Pt-like d-band center of PdO@WO3Sx 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.