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Abstract This study investigates the grain boundary energy dependence on segregated dopants in nanocrystalline zinc aluminate ceramics. Atomistic simulations of Σ3 and Σ9 grain boundaries showed that trivalent ions of varying ionic radii [Sc³⁺(74.5 pm), In³⁺(80.0 pm), Y³⁺(90.0 pm), and Nd³⁺(98.3 pm)] have a tendency to segregate to both interfaces, with Y³⁺presenting the highest segregation potentials. The connection between segregation and the reduction of interfacial energies was explored by measuring the grain boundary energy on nanoceramics fabricated via high‐pressure spark plasma sintering (HP‐SPS) using differential scanning calorimetry (DSC). The results revealed that Y³⁺doping at 0.5 mol% reduces the grain boundary energy in zinc aluminate nanoceramics from 1.1–1.3 J/m²to 0.6–0.8 J/m²; the range correlates with the observed size dependence of the excess energy, with higher values observed for the smaller grain sizes (∼17 nm). The noted decrease in interfacial energies for doped samples suggests it is indeed possible to alter the stability of zinc aluminate grain boundaries via dopant segregation. 

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.