Hybrid materials photocatalysts based on conjugated polymers and inorganic semiconductors provide a sustainable way to remove pollutants or store energy in the form of solar fuels by processes such as water splitting, CO₂photoreduction and NH₃production (artificial photosynthesis).

Transition metal chalcogenides have been identified as low-cost and efficient electrocatalysts to promote the hydrogen evolution reaction in alkaline media. However, the identification of active sites and the underlying catalytic mechanism remain elusive. In this work, we employ operando X-ray absorption spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy to elucidate that NiS undergoes an in-situ phase transition to an intimately mixed phase of Ni₃S₂ and NiO, generating highly active synergistic dual sites at the Ni₃S₂/NiO interface. The interfacial Ni is the active site for water dissociation and OH* adsorption while the interfacial S acts as the active site for H* adsorption and H₂ evolution. Accordingly, the in-situ formation of Ni₃S₂/NiO interfaces enables NiS electrocatalysts to achieve an overpotential of only 95 ± 8 mV at a current density of 10 mA cm⁻². Our work highlighted that the chemistry of transition metal chalcogenides is highly dynamic, and a careful control of the working conditions may lead to the in-situ formation of catalytic species that boost their catalytic performance.

In this review article, we summarise the key electronic features of transition metal oxides that govern their OER catalytic properties, and how such electronic descriptors are applied for OER electrocatalysts design.

Sunlight plays a critical role in the development of emerging sustainable energy conversion and storage technologies. Light-induced CO₂ reduction by artificial photosynthesis is one of the cornerstones to produce renewable fuels and environmentally friendly chemicals. Interface interactions between plasmonic metal nanoparticles and semiconductors exhibit improved photoactivities under a wide range of the solar spectrum. However, the photo-induced charge transfer processes and their influence on photocatalysis with these materials are still under debate, mainly due to the complexity of the involved routes occurring at different timescales. Here, we use a combination of advanced in situ and time-resolved spectroscopies covering different timescales, combined with theoretical calculations, to unravel the overall mechanism of photocatalytic CO₂ reduction by Ag/TiO₂ catalysts. Our findings provide evidence of the key factors determining the enhancement of photoactivity under ultraviolet and visible irradiation, which have important implications for the design of solar energy conversion materials.