Enhancing the photocatalytic water electrolysis performance of Zn ₂ SnO ₄ nanostructures via post-synthesis nitrogen doping

Nitrogen-doped Zn₂SnO₄ nanostructures were developed via hydrothermal treatment. Urea (CH₄N₂O) was used as the nitrogen source to achieve post-growth nitrogen doping in Zn₂SnO₄ nanostructures. Nitrogen doping resulted in morphological distortion. The elemental study proved that nitrogen concentration increased with an increase in the concentration of urea in the precursor solutions. The vibration modes corresponding to the Zn-N and Sn-N bonds confirmed the incorporation of nitrogen into the crystal lattice of Zn₂SnO₄. XPS analysis revealed that higher nitrogen doping concentrations led to the substitutional incorporation of nitrogen. Nitrogen doping in Zn₂SnO₄ introduced impurity levels in the electronic band structure and reduced its optical band gap (from 2.7 eV to 2.4 eV). Consequently, the Zn₂SnO₄ nanostructure with approximately 1.9 at% nitrogen showed the highest photocurrent density of 124 μA cm^-2 at 1.23 V vs. RHE, representing approximately 2.6-fold improvement in photocurrent compared to that of undoped Zn₂SnO₄ nanostructures. Optimized nitrogen doping resulted in approximately 89% charge injection efficiency along with the lowest charge transfer resistance.