Ag → NiO electron cascade-driven cocatalysts enable efficient photocatalytic ammonia-to-hydrogen conversion

Suppressing photoinduced charge recombination represents a critical challenge in photocatalytic ammonia (NH₃) decomposition for hydrogen (H₂) production. Herein, we propose a dual-cocatalyst system comprising plasmonic silver (Ag) and nickel oxide (NiO), which synergistically construct an Ag → titanium dioxide (TiO₂) → NiO directional electron cascade on TiO₂ surfaces through work-function-induced interfacial charge transfer. The optimized 3 %Ag-1 %NiO-TiO₂ reaches a significantly photocatalytic H₂ production rate of 2366.9 μmol/h/g from NH₃ splitting, which is 20.7, 2.1 and 1.5 folds higher than that of pristine TiO₂ (114.4 μmol/h/g), 1 %NiO-TiO₂ (1146.7 μmol/h/g) and 3 %Ag-TiO₂ (1534.1 μmol/h/g), respectively. Photoelectric characterizations confirm accelerated charge separation and transfer dynamics through synergistic interplay of NiO and Ag cocatalysts on TiO₂. Density functional theory (DFT) calculations reveal that work function gradient among TiO₂, NiO and Ag facilitates unidirectional electron flow from Ag to NiO through the TiO₂ bridge. The optimal nickel (Ni) d-band center position and the reduced potential-determining step energy barrier for NH₃ splitting on 3 %Ag-1 %NiO-TiO₂ are further identified as key factors governing its outstanding H₂ evolution performance. This work establishes a rational dual-cocatalyst design with unidirectional electron flow to enable efficient photocatalytic H₂ production from NH₃ splitting.