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Safe deployment of hydrogen as a clean energy carrier demands gas sensors capable of detecting leaks at sub-ppm concentrations with fast response, low power consumption, and straightforward integration into process monitoring systems. Here we report a palladium nanoparticle-decorated Graphene/Silicon (Pd-G/Si) Schottky junction diode that addresses these requirements through a deliberate combination of reverse-bias operation and thermal activation near the Pd hydride dissociation temperature. Palladium nanoparticles serve as a chemical sensitizer. Operating under reverse bias at −0.8 V and 120°C – a temperature regime that maximizes PdHₓ formation kinetics without entering the hydride dissociation regime above ∼150°C – the device achieves a detection limit of 0.5 ppm with response and recovery times of 20 s and 90 s, respectively, at a bias-power consumption below 0.2 µW. Current-noise analysis confirms that the −0.8 V reverse bias minimizes current fluctuations and produces a white-noise-dominated low-frequency spectrum only moderately sensitive to temperature, preserving a favorable signal-to-noise ratio. Arrhenius analysis of the response and recovery kinetics yields PdHₓ dissociation energies consistent with those of dilute α-phase PdHₓ, corroborating the thermally controlled sensing mechanism. The sensing area is inherently miniaturized, confined to the narrow conduction channel at the graphene/Si edge, so that only a small fraction of the surface requires PdNP coverage, reducing fabrication cost relative to large-area architectures. The Pd-G/Si Schottky diode delivers sub-ppm H₂ detection through simple two-terminal current measurements without specialized instrumentation – establishing it as a promising, cost-effective platform for hydrogen safety monitoring in the ppm-to-ppb concentration range.

Copper–zinc oxide pn-type heterostructures are promising visible-light-active photocatalysts because their intrinsic bandgaps and band alignment facilitate efficient charge separation. However, achieving controlled deposition of copper oxide nanoparticles on ZnO nanorods remains challenging, particularly in forming well-defined interfaces. Here, we report a UV-assisted photo-deposition method using [Cu(EDTA)]2− complexes to predominantly form Cu2O nanoparticles on sea-urchin-like ZnO nanorods that either were used as-prepared or subjected to systematic post-heating treatments. The structural, chemical, and electronic properties of the resulting pn-type heterostructures were characterized by X-ray diffraction, electron microscopy, and photoelectron and photoluminescence spectroscopy, while phenol photodegradation products were quantified by HPLC. In contrast to the as-prepared ZnO nanorods, annealing treatment prior to Cu2O deposition produces well-developed Cu2O–ZnO interfaces, yielding pn-type heterostructures with enhanced photocatalytic degradation of phenol under UVA illumination. Our results indicate improved interfacial charge transfer, attributed to reduced lattice defects and removal of surface contaminants through annealing. These findings demonstrate that substrate surface preparation combined with atom-by-atom photo-deposition of chelated copper complexes provides a straightforward route for optimizing heterostructure catalysts with improved interfacial properties and enhanced photocatalytic activity.

We report on the surface chemical and photocatalytic properties of hierarchical ZnO nanorod assemblies synthesized via zinc acetate-based methods and subjected to various pretreatment protocols. The as-prepared ZnO samples were thoroughly washed and thermally treated at different temperatures and durations to remove residual organics from the synthesis. Despite extensive washing, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy revealed significant amounts of residual organic species on the as-prepared ZnO surfaces. Operando DRIFTS demonstrated that annealing to 500 °C was required to effectively eliminate these synthesis-related residues. However, prolonged annealing also led to the removal of two types of ZnO-associated defects: (i) terminal −OH groups, which reformed upon cooling in synthetic air, and (ii) intrinsic lattice defects hosting bridge-bonded OH species, which were irreversibly healed. The catalytic performance of the ZnO samples, assessed by phenol photodegradation and its decomposition products, showed enhanced activity for washed and calcined ZnO (up to 52% degradation) compared to as-prepared samples treated only by chemical washing (24% degradation). Operando DRIFTS revealed that extended thermal treatment at 500 °C led to a decline in catalytic activity (34% degradation) relative to samples exposed to shorter annealing times. This loss in activity was directly correlated with a decreased concentration of catalytically active lattice vacancy defects. Our findings provide molecular-level evidence of two competing effects during thermal pretreatment of ZnO in oxidizing environments: the removal of inhibitory organic residues (which enhances activity) and the healing of reactive lattice defects (which reduces activity). These results underscore the critical importance of optimizing pretreatment conditions when designing efficient ZnO-based catalysts from organic zinc precursors and highlight the essential role of lattice defects in governing ZnO surface reactivity.