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Abstract This work investigates the effects of doping on both the thermodynamics and kinetics of sintering in aluminum‐doped yttrium oxide nanoparticles (Al‐doped Y₂O₃), with the objective of delineating their interdependent effects at different stages of the process. Direct measurements of surface and grain boundary energies using differential scanning calorimetry showed that Al‐doping decreases both interfacial energies, leading to an increase in dihedral angle (from 152.7 ± 5.6° to 165.8 ± 5.5°) and, therefore, sintering stress. Densification and grain growth analyses showed that despite this increase in sintering stress, the onset of sintering is delayed for the Al‐doped samples, demonstrating that a large dihedral angle is a necessary but not sufficient condition for densification. The measurements of activation energies for densification and grain growth point out that Al suppresses grain boundary mobility by increasing the activation energy from 400 to 448 kJ/mol, hindering densification at the intermediate stages of sintering. At temperatures above 1150℃, grain growth is activated in the Al‐doped samples, which rapidly releases the accumulated sintering stress and exhibits a higher densification rate than in undoped Y₂O₃. This study demonstrates a complex interconnectivity between the thermodynamics and kinetics at different temperature ranges of sintering and reinforces the need for a comprehensive description for proper design of sintering aids. 

Hematite nanostructures are strong candidates for the development of sustainable water splitting technologies. However, major challenges exist in improving charge density and minimizing charge recombination rates for a competitive photoelectrochemical performance based on hematite without compromising sustainability aspects. Here we develop a synthetic strategy to leverage earth-abundant Al3+ and Zr4+ in a dual-chemical modification to synergistically minimize small polaron effects and interfacial charge recombination. The solution-based method simultaneously induces Al3+ doping of the hematite crystal lattice while Zr4+ forms interfacial excess, creating a single-phased homogeneous nanostructured thin film. The engineered photoanode increased photocurrent from 0.7 mA cm-2 for pristine hematite up to 4.5 mA cm-2 at 1.23 V and beyond 6.0 mA cm-2 when applying an overpotential of 300 mV under simulated sunlight illumination (100 mW cm-2). The results demonstrate the potential of dual-modification design using solution-based processes to enable sustainable energy technologies. 

Scaling up photoelectrochemical (PEC) devices for green hydrogen production is a significant challenge that requires robust and cost-effective production methods. In this study, hematite photoelectrodes has been synthesized using a cost-effective polymeric precursor solution, resulting in homogeneous ultra-thin films (~125 nm) with areas up to 200 cm2. We observed a substantial photocurrent drop as photoelectrode area increases, addressed by modifying the precursor solution with Hf4+. This modification improves the morphology and films adherence, leading to simultaneous grain|grain interface segregation and a modified FTO|hematite interface. As a result, film conductivity increases, reducing the photocurrent drop at larger photoelectrode areas. The improved charge separation and surface charge injection efficiencies allows a homogeneous photocurrent of 1.6 mA cm⁻2 at 1.45V across a 15.75 m2 electrode area, using less than 70 μg of photoactive material. Cost analysis study indicates that this low-energy fabrication method is a significant step forward in green hydrogen production, contributing to sustainable and efficient green hydrogen technologies. 

Interface segregation plays a governing role in nanocrystalline ceramics properties due to the relative increase in the interfacial volume fraction. However, due to the complexity of the detection and quantification of interfacial excesses at the nanoscale, the role of ionic dopants or additives on microstructural evolution and thermodynamics can be easily underestimated. In this work, we address the spatial distribution of Li⁺as a dopant in magnesium aluminate spinel nanoparticles. This is achieved through a novel method for the detection and quantification of Li⁺across the surface, grain boundary, and bulk (crystal lattice). Based on selective lixiviation combined with chemical analysis, we were able to quantify the amount of Li⁺forming surface excess, whereas the quantitative solid‐state nuclear magnetic resonance technique enabled the quantification of Li⁺segregated in the grain boundaries and dissolved in the lattice. This comprehensive understanding of the Li⁺distribution across the nanoparticles makes possible an unprecedented interpretation of coarsening and sintering, with a clear correlation between the microstructure and the Li⁺distribution. Although the work focuses on MgAl₂O₄, the proposed combination of techniques is expected to have a positive impact on the understanding of other multicomponent nanoscale systems. 

The work demonstrates a three-fold increase in photoelectrochemical efficiency of hematite nanorods as a result of the combination of Hafnium surface doping and the incorporation of a ZrO2 underlayer on FTO. While the ZrO2 layer reduced the electron loss from the back-injection into the FTO contact support, Hafnium surface doping did not significantly alter the hematite lattice structure. But rather, Hafnium induced nanorod diameter reduction from 32 ± 2 and 26 ± 2 nm, with a consequent increase in the active surface area. The linear sweep voltammetry measurements with 100 mW cm−2 illumination in a 500 nm photoanode thickness showed a photocurrent density of 2.07 mA cm−2 at 1.23 V in a reversible hydrogen electrode (RHE). The value contrasts with the bare hematite rods (0.75 mA cm−2), highlighting the photoanode design's role in improving solar power hydrogen production.