Attributing to their distinct thickness and surface dependent physicochemical properties, two dimensional (2D) nanostructures have become an area of increasing interest for interfacial interactions. Effectively, properties such as high surface-to-volume ratio, modulated surface activities and increased control of oxygen vacancies make these types of materials particularly suitable for gas-sensing applications. This work reports a facile wet-chemical synthesis of 2D tungsten oxide nanosheets by sonication of tungsten particles in an acidic environment and thermal annealing thereafter. The resultant product of large nanosheets with intrinsic substoichiometric properties is shown to be highly sensitive and selective to nitrogen dioxide (NO₂) gas, which is a major pollutant. The strong synergy between polar NO₂ molecules and tungsten oxide surface and also abundance of active surface sites on the nanosheets for molecule interactions contribute to the exceptionally sensitive and selective response. An extraordinary response factor of ∼30 is demonstrated to ultralow 40 parts per billion (ppb) NO₂ at a relatively low operating temperature of 150 °C, within the physisorption temperature band for tungsten oxide. Selectivity to NO₂ is demonstrated and the theory behind it is discussed. The structural, morphological and compositional characteristics of the synthesised and annealed materials are extensively characterised and electronic band structures are proposed. The demonstrated 2D tungsten oxide based sensing device holds the greatest promise for producing future commercial low-cost, sensitive and selective NO₂ gas sensors.

Sulfur-rich molybdenum sulfides are an emerging class of inorganic coordination polymers that are predominantly utilized for their superior catalytic properties. Here we investigate surface water dependent properties of sulfur-rich MoS_x (x = 3²/₃) and its interaction with water vapor. We report that MoS_x is a highly hygroscopic semiconductor, which can reversibly bind up to 0.9 H₂O molecule per Mo. The presence of surface water is found to have a profound influence on the semiconductor’s properties, modulating the material’s photoluminescence by over 1 order of magnitude, in transition from dry to moist ambient. Furthermore, the conductivity of a MoS_x-based moisture sensor is modulated in excess of 2 orders of magnitude for 30% increase in humidity. As the core application, we utilize the discovered properties of MoS_x to develop an electrolyteless water splitting photocatalyst that relies entirely on the hygroscopic nature of MoS_x as the water source. The catalyst is formulated as an ink that can be coated onto insulating substrates, such as glass, leading to efficient hydrogen and oxygen evolution from water vapor. The concept has the potential to be widely adopted for future solar fuel production.

Two-dimensional (2D) transition metal chalcogenides such as 2D MoS₂ are considered prime candidate materials for the design of next generation optoelectronics. Functionalisation of these materials is considered to be a key step in tailoring their properties towards specific applications and unlocking their full potential. Here we present a van der Waals functionalisation strategy for creating MoS₂ nanosheets decorated with free base phthalocyanine chromophores. The semiconducting sheets are found to intimately interact with these optoelectronically active chromophores, resulting in an electronic heterostructure that exhibits enhanced optoelectronic properties and exploitable charge transfer. We show that by utilising laterally confined MoS₂ nanosheets, the conduction band of the semiconductor could be positioned between the chromophore's S1 and S2 states. Consequently, bidirectional photoinduced electron transfer processes are observed, with excitation of the functionalised nanosheet's semiconductor transition resulting in electron transfer to the phthalocyanine's LUMO, and excitation of the chromophore's S2 state leading to electron injection into the MoS₂ conduction band. However, charge transfer from the dye's S1 transition to the MoS₂ nanosheet is found to be thermodynamically unfavourable, resulting in intense radiative recombination. These findings may enable controlling and tuning the charge carrier density of semiconducting nanosheets via optical means through the exploitation of photoinduced electron transfer. Furthermore this work provides access to 2D semiconductor-hybrids with tailored absorption profiles and photoluminescence.

The demand for green hydrogen as an energy carrier is projected to exceed 350 million tons per year by 2050, driven by the need for sustainable distribution and storage of energy generated from sources. Despite its potential, hydrogen production currently faces challenges related to cost efficiency, compliance, monitoring, and safety. This work proposes Hydrogen 4.0, a cyber–physical approach that leverages Industry 4.0 technologies—including smart sensing, analytics, and the Internet of Things (IoT)—to address these issues in hydrogen energy plants. Such an approach has the potential to enhance efficiency, safety, and compliance through real-time data analysis, predictive maintenance, and optimised resource allocation, ultimately facilitating the adoption of renewable green hydrogen. The following sections break down conventional hydrogen plants into functional blocks and discusses how Industry 4.0 technologies can be applied to each segment. The components, benefits, and application scenarios of Hydrogen 4.0 are discussed while how digitalisation technologies can contribute to the successful integration of sustainable energy solutions in the global energy sector is also addressed.