The urea oxidation reaction (UOR), requiring less energy to produce hydrogen, is considered as a potential alternative to the traditional oxygen evolution reaction. Consequently, developing highly efficient UOR catalysts to facilitate H₂ production has garnered widespread attention. A promising approach to enhancing the effectiveness of these electrocatalysts is defect engineering. By introducing structural defects, defect engineering can expose more active sites and optimize their electronic structure, thereby improving their activity. This work offers a comprehensive overview of recent progress in defect engineering of nickel-based electrocatalysts for the UOR. It summarizes various strategies for generating defects, including the creation of vacancies, doping, the incorporation of single atoms, amorphization, and achieving high refractivity. Furthermore, we discuss the advanced characterization techniques commonly used to identify the presence of defects in these electrocatalysts, as well as to determine their detailed structures. Finally, we outline the prospects and challenges associated with the systematic design and fabrication of novel UOR electrocatalysts with tunable defects, aiming to further enhance their efficiency and stability.

Antimicrobial photodynamic therapy (aPDT) offers a promising non-antibiotic alternative for localized infections; however, its efficacy is frequently compromised by photosensitizer aggregation and rapid washout. Here, we report a bio-hybrid platform that combines the biopolymer chitosan with the biomineral hydroxyapatite to host methylene blue (MB) as a scaffold-associated photosensitizer. The resulting methylene blue-loaded chitosan/hydroxyapatite composite (MB@CS/HAp) was prepared by in situ mineralization and exhibited an effective retained MB loading of 1.2 wt%. Structural and physicochemical characterization confirmed successful composite formation and non-covalent MB incorporation. The CS/HAp scaffold exhibited a mesoporous structure with a BET specific surface area of 14.6 m2 g–1, providing a favorable host matrix that supports MB association and is designed to limit excessive self-aggregation while helping to preserve a more photoactive dispersed state.,Mass-balance and desorption studies indicated substantial MB retention, with a cumulative desorbed fraction of 27.8 ± 0.7% after 12 h under physiological conditions. Under the tested short-contact aPDT conditions, MB@CS/HAp achieved complete inhibition of Escherichia coli and Staphylococcus aureus at composite concentrations of 0.25 and 0.03 mg mL⁻1, respectively (at 15 J cm⁻2). When normalized to MB content, this corresponds to MB-equivalent MICs of 3.0 µg mL⁻1 for E. coli and 0.36 µg mL⁻1 for S. aureus, representing ~21-fold and ~11-fold reductions in the required MB dose relative to free MB. Molecular dynamics simulations showed that MB is stabilized at the CS/HAp interface via electrostatic and hydrogen-bonding interactions, resulting in reduced mobility and improved desorption resistance. These results together establish MB@CS/HAp as a biopolymer–biomineral, scaffold-associated photosensitizer platform and provide design guidance for localized solid-state aPDT materials.