Integration of Oxygen-Vacancy-Rich NiFe-Layered Double Hydroxide onto Silicon as Photoanode for Enhanced Photoelectrochemical Water Oxidation

Mg-doped α-Ga2O3 Nanorods for the Construction of Photoelectrochemical-Type Self-Powered Solar Blind UV Photodetectors and Underwater Imaging Application

Underwater imaging technologies are increasingly crucial for environmental monitoring and resource exploration. However, the development of advanced photodetectors for such applications faces significant challenges, including interference from ambient visible and infrared light, adaptation to underwater environments, and cost-effectiveness. Photoelectrochemical-type solar-blind photodetectors (PEC-SBPDs) based on wide bandgap semiconductors have shown great promise in overcoming these challenges. Here, a novel approach to enhance the performance of α-Ga2O3-based PEC-SBPDs is presented for underwater imaging through Mg-doping. By employing a low-cost hydrothermal synthesis technique, Mg-doped α-Ga2O3 nanorod arrays are fabricated, which induces the formation of VO-MgGa complexes that enhances the interfacial catalytic activity and improves the transport of photogenerated carriers. The optimized PEC-SBPDs exhibits a remarkable 435% increase in photocurrent response compared to undoped α-Ga2O3, with a peak responsivity of 34.54 mA W-1. A 5 × 5 PEC-SBPD array based on Mg-doped α-Ga2O3 nanorods is successfully demonstrated for underwater solar-blind imaging, achieving clear and efficient imaging in challenging underwater conditions. This study not only highlights the superior performance of Mg-doped α-Ga2O3 in underwater environments but also opens new avenues for the development of high-performance self-powered photodetectors in imaging, sensing, and other related applications.

High-Valence Metals Accelerate the Reaction Kinetics for Boosting Water Oxidation

The transition metal with high valence state in oxyhydroxides can accelerate the reaction kinetics, enabling highly intrinsic OER activity. However, the formation of high-valence transition-metal ions is thermodynamically unfavorable in most cases. Here, a novel strategy is proposed to realize the purpose and reveal the mechanism by constructing amorphous phase and incorporating of elements with the characteristic of Lewis acid or variable charge state. A model catalyst, CeO2-NiFeOxHy, is presented to achieve the modulation of valence state of active site (Ni2+→Ni3+→Ni4+) for improved OER, leading to dominant active sites with high valence state. The CeO2-NiFeOxHy electrode exhibits superior OER performance with overpotential of 214 and 659 mV at 10 and 500 mA cm-2, respectively (without IR correction), and high stability, which are much better than those of NiOxHy, NiFeOxHy and CeO2-NiOxHy. These findings provide an effective strategy to achieve the active metals with high-valence state for highly efficient OER.

Scalable, highly stable Si-based metal-insulator-semiconductor photoanodes for water oxidation fabricated using thin-film reactions and electrodeposition

Metal-insulator-semiconductor (MIS) structures are widely used in Si-based solar water-splitting photoelectrodes to protect the Si layer from corrosion. Typically, there is a tradeoff between efficiency and stability when optimizing insulator thickness. Moreover, lithographic patterning is often required for fabricating MIS photoelectrodes. In this study, we demonstrate improved Si-based MIS photoanodes with thick insulating layers fabricated using thin-film reactions to create localized conduction paths through the insulator and electrodeposition to form metal catalyst islands. These fabrication approaches are low-cost and highly scalable, and yield MIS photoanodes with low onset potential, high saturation current density, and excellent stability. By combining this approach with a p⁺n-Si buried junction, further improved oxygen evolution reaction (OER) performance is achieved with an onset potential of 0.7 V versus reversible hydrogen electrode (RHE) and saturation current density of 32 mA/cm² under simulated AM1.5G illumination. Moreover, in stability testing in 1 M KOH aqueous solution, a constant photocurrent density of ~22 mA/cm² is maintained at 1.3 V versus RHE for 7 days.

Authors demonstrate Si-based MIS photoanodes using Al thin-film reactions to create localized conduction paths through the insulator and Ni electrodeposition to form metal catalyst islands. These approaches yielded low onset potential, high saturation current density, and excellent stability.

Electrodeposited Trimetallic NiFeW Hydroxide Electrocatalysts for Efficient Water Oxidation

Tungsten-doped Ni-Fe hydroxides fabricated on a three-dimensional nickel foam through cathodic electrodeposition are proposed as effective oxygen evolution reaction (OER) catalysts for alkaline water oxidation. Incorporating an adequate amount of W into Ni-Fe hydroxides modulates the electronic structure by changing the local environment of Ni and Fe and create oxygen vacancies, resulting in abundant active sites for the OER. The optimized electrocatalyst, with a substantial number of catalytic sites, is found to outperform the well-established 20 wt% Ir/C electrocatalyst. The catalyst only requires small overpotentials of 224 mV and 251 mV to generate current densities of 10 mA cm^-2 and 50 mA cm^-2 , respectively, at an extremely low Tafel slope. Surface study after long-term chronopotentiometry (ca. 30 h) reveals that the tungsten dopant undergoes reduction to stabilize the Ni and Fe active sites for predominant water oxidation. This research provides new insight to apply optimum amounts of tungsten doping to enable more significant electronic coupling within Ni-Fe for the chemisorption of hydroxy and oxygen intermediates and greatly improved OER activity.