Hydrogen detection is a critical component of safety and efficiency in hydrogen-based systems, from fuel cells to storage infrastructure. Recent advances in materials science have identified graphene and other two-dimensional materials as promising candidates for hydrogen sensing due to their exceptional electronic properties, high surface-to-volume ratios, and tunable chemical reactivity. These materials enable detection mechanisms based on resistivity changes or work function modulation, offering ultra-high sensitivity and room-temperature operation—key advantages over conventional metal-oxide or palladium-based sensors. However, challenges such as reproducibility, environmental stability, and scalable fabrication remain significant hurdles.

Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, exhibits extraordinary electrical conductivity and minimal noise, making it highly responsive to surface adsorbates. When hydrogen molecules interact with graphene, they induce charge transfer, altering the material’s resistivity. Studies have demonstrated that pristine graphene can detect hydrogen at concentrations as low as 1 part per million (ppm) at room temperature. The absence of bandgap in graphene, however, limits its selectivity, prompting the exploration of modified or hybrid structures. For instance, graphene decorated with palladium nanoparticles enhances both sensitivity and selectivity due to palladium’s intrinsic hydrogen affinity. The nanoparticles dissociate hydrogen molecules into atoms, which then spill over onto the graphene surface, inducing measurable resistance changes.

Transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), offer complementary advantages. Unlike graphene, MoS2 possesses a tunable bandgap, which can be engineered for specific sensing applications. Monolayer MoS2 exhibits n-type semiconducting behavior, and its conductivity is highly sensitive to hydrogen adsorption. Experimental results indicate that MoS2-based sensors achieve detection limits below 10 ppm with response times under 30 seconds at ambient conditions. The sensing mechanism involves hydrogen atoms binding to sulfur vacancies, altering the charge carrier density. However, the performance of MoS2 sensors is highly dependent on defect density and layer thickness, leading to variability in device reproducibility.

Phosphorene, a single layer of black phosphorus, has emerged as another contender due to its anisotropic electronic properties and high carrier mobility. Unlike graphene and MoS2, phosphorene demonstrates a strong dependence of resistivity on hydrogen adsorption along specific crystal orientations. This anisotropy can be exploited for directional sensing applications. However, phosphorene’s susceptibility to oxidation under ambient conditions poses a significant challenge for long-term stability. Encapsulation strategies using inert layers like hexagonal boron nitride (hBN) have been explored to mitigate degradation, though these add complexity to fabrication.

Hybrid material systems combine the strengths of multiple 2D materials to overcome individual limitations. For example, graphene-MoS2 heterostructures leverage graphene’s high conductivity and MoS2’s bandgap for improved selectivity and sensitivity. In such configurations, hydrogen adsorption on MoS2 modulates the interfacial charge transfer between the layers, producing a measurable signal. Similarly, graphene-phosphorene hybrids exploit phosphorene’s anisotropic response while using graphene as a protective and conductive scaffold. These hybrid designs often outperform single-material sensors, achieving sub-ppm detection limits and faster recovery times.

Scalable fabrication techniques are essential for transitioning laboratory-scale sensors into commercial applications. Chemical vapor deposition (CVD) is the most widely used method for producing large-area graphene and TMD films, though defects and grain boundaries can affect sensor uniformity. Solution-based methods, such as liquid-phase exfoliation, offer cost-effective alternatives but struggle with controlling layer thickness and material quality. Recent advances in roll-to-roll processing and inkjet printing have shown promise for high-throughput fabrication of 2D material sensors, though challenges in material consistency and device integration persist.

Reproducibility remains a critical issue for 2D material-based hydrogen sensors. Variability in material synthesis, transfer processes, and environmental exposure can lead to inconsistent performance. Standardization of fabrication protocols and rigorous testing under real-world conditions are necessary to address this challenge. Additionally, long-term stability under fluctuating humidity and temperature conditions requires further investigation, as atmospheric interactions can degrade sensor performance over time.

In summary, graphene, MoS2, and phosphorene offer compelling advantages for hydrogen sensing, including ultra-high sensitivity and room-temperature operation. Hybrid designs and advanced fabrication techniques are paving the way for more robust and scalable solutions. However, achieving commercial viability demands continued research into material stability, reproducibility, and large-scale manufacturing. As hydrogen technologies expand across industries, the development of reliable and efficient sensors will be paramount to ensuring safety and operational efficiency.