Atomically isolated Pd sites within Pd-S nanocrystals enable trifunctional catalysis for direct, electrocatalytic and photocatalytic syntheses of H₂O₂

Although high-efficiency production of hydrogen peroxide (H₂O₂) can be realized separately by means of direct, electrochemical, and photocatalytic synthesis, developing versatile catalysts is particularly challenging yet desirable. Herein, for the first time we reported that palladium-sulphur nanocrystals (Pd-S NCs) can be adopted as robust and universal catalysts, which can realize the efficient O₂ conversion by three methods. As a result, Pd-S NCs exhibit an excellent selectivity (89.5%) to H₂O₂ with high productivity (133.6 mol·kg_cat⁻¹·h⁻¹) in the direct synthesis, along with the significantly enhanced H₂O₂ production activity and stability via electrocatalytic and photocatalytic syntheses. It is demonstrated that the isolated Pd sites can enhance the adsorption of O₂ and inhibit its O–O bond dissociation, improving H₂O₂ selectivity and reducing H₂O₂ degradation. Further study confirms that the difference in surface atom composition and arrangement is the key factor for different ORR mechanisms on Pd NCs and Pd-S NCs.