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Using heterogeneous photocatalysts for harvesting sunlight and converting it for water remediation and splitting are promising to mitigate the possible crisis of environment and energy. Among various composites, the MoS2‐based heterostructures and Ni‐based systems exhibit unique electronic, optical properties and redox capabilities, enabling their roles as photocatalysts. Herein, the impacts of chemical environments on the Ni electronic structures within the MoS2‐Ag‐Ni ternary systems are studied via X‐ray photoemission electron spectroscopy (X‐PEEM). Ni nanoparticles with two different sizes of 70 and 200 nm were loaded to MoS2 flakes with silver buffers as bridges. Heterostructures with a nominal mol percentage of (MoS2)77Ag3.7Ni19.3 were synthesized through an ultrasound‐assisted wet method. The oxidation states and various interfacial interactions of Ni with MoS2 in MoS2‐Ag‐Ni ternary composite are spectromicroscopically determined, combining the X‐ray absorption spectroscopy near Ni L‐edges and the imaging capability of the X‐PEEM. Results showed that Ni mainly retrains its chemical states of metal and native oxidizations without observable electronic features subjected to bonding with the sulfur from the MoS2 flakes. The charge migration channel set up by the Ag buffer thus contributes to electron–hole migrations that facilitate the photocatalytic performance of the ternary system eventually. [ABSTRACT FROM AUTHOR]

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This work employs ambient pressure X-ray photoelectron spectroscopy (APXPS) to delve into the atomic and electronic transformations of a core-shell Ni@NiO/NiCO 3 photocatalyst - a model system for visible light active plasmonic photocatalysts used in water splitting for hydrogen production. This catalyst exhibits reversible structural and electronic changes in response to water vapor and solar simulator light. In this study, APXPS spectra were obtained under a 1 millibar water vapor pressure, employing a solar simulator with an AM 1.5 filter to measure spectral data under visible light illumination. The in situ APXPS spectra indicate that the metallic Ni core absorbs the light, exciting plasmons, and creates hot electrons that are subsequently utilized through hot electron injection in the hydrogen evolution reaction (HER) by NiCO 3 . Additionally, the data show that NiO undergoes reversible oxidation to NiOOH in the presence of water vapor and light. The present work also investigates the contribution of carbonate and its involvement in the photocatalytic reaction mechanism, shedding light on this seldom-explored aspect of photocatalysis. The APXPS results highlight the photochemical reduction of carbonates into -COOH, contributing to the deactivation of the photocatalyst. This work demonstrates the APXPS efficacy in examining photochemical reactions, charge transfer dynamics and intermediates in potential photocatalysts under near realistic conditions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Visible light-active nickel-based plasmonic photocatalysts provide a cost-effective alternative to noble metals. However, their rarity, fragility, and limited understanding pose challenges. This work presents a microwave-assisted organic synthesis of a Ni-NiO@Ni 2 CO 3 (OH) 2 core-shell@sheet plasmonic photocatalyst. By employing time and power dependent synthesis, this catalyst exhibits flexible Ni 2 CO 3 (OH) 2 nanosheets enveloping the Ni-NiO structure, surpassing the pristine Ni@NiO/NiCO 3 core-shell counterpart. Chemical reaction mechanisms suggest that irradiation of pristine Ni-NiO/NiCO 3 nano structures leads to breakage of amorphous NiCO 3 to Ni 2+ and CO 3 2- , which further, in the presence of water solvent, interacts with OH - ions leading to the formation of Ni(CO 3 )·Ni(OH) 2 . With enhanced light absorption and photocatalytic properties, the resulting core-shell@sheet photocatalyst demonstrates double the hydrogen evolution reaction yield (40 μmol g -1 h -1 ) compared to the pristine catalyst (20 μmol g -1 h -1 ). The enhanced H 2 yield is attributed to the flexible sheets, cross-dimensional photocatalyst structure, increased surface area for surface reactions, and higher H 2 activity of Ni 2 CO 3 (OH) 2 . This research showcases the potential of microwave-assisted synthesis in developing flexible nanosheets with superior solar water splitting performance., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Ni@NiO/NiCO 3 core-shell nanostructures have been investigated for surface plasmon driven photocatalytic solar H 2 generation without any co-catalyst. Huge variation in the photocatalytic activity has been observed in the pristine vs. post-vacuum annealed samples with the maximum H 2 yield (∼110 μmol g -1 h -1 ) for the vacuum annealed sample (N70-100/2 h) compared to ∼92 μmol g -1 h -1 for the pristine (N70) photocatalyst. Thorough structural (X-ray diffraction) and spectroscopic (X-ray photoelectron spectroscopy and transmission electron microscopy coupled electron energy loss spectroscopy) investigations reveal the core Ni nanoparticle decorated with the shell, a composite of crystalline NiO and amorphous NiCO 3 . Significant visible light absorption at ∼475 nm in the UV-vis region along with the absence of a peak/edge corresponding to NiO suggest the role of surface plasmons in the observed catalytic activity. As per the proposed mechanism, amorphous NiCO 3 in the shell has been suggested to serve as the dielectric medium/interface, which enhances the surface plasmon resonance and boosts the HER activity., Competing Interests: There are no conflict of interests to declare., (This journal is © The Royal Society of Chemistry.)