Sustainable and Energy-Efficient Hydrogen Generation from NaBH₄ Methanolysis Enabled by Nb₂O₅ Synthesized through a...

A pressureless microwave-assisted hydrothermal route is presented for the synthesis of highly active amorphous niobium pentoxide (Nb₂O₅·nH₂O) nanostructures and their application as metal oxide catalysts for hydrogen generation via sodium borohydride methanolysis. The synthesis, conducted at sub-boiling temperature (75 °C) under open-vessel conditions, produces a microporous Nb₂O₅ material with a very high specific surface area (230 m² g^-1), abundant surface hydroxyl groups, and a predominance of weak-to-moderate acidic sites. Structural and surface analyses reveal a disordered NbO₆ network enriched with terminal NbO species and undercoordinated oxygen environments, which are absent in crystalline commercial Nb₂O₅. In NaBH₄ methanolysis, the amorphous Nb₂O₅ catalyst achieves a hydrogen generation rate of 22,781.7 mL min^-1 g^-1 at 25 °C with a low apparent activation energy of 21.95 kJ mol^-1, outperforming many reported noble-metal-based catalysts. Reaction kinetics follow a first-order dependence on NaBH₄ concentration, and the catalyst maintains stable activity over multiple reuse cycles. In addition, machine learning-assisted analysis was employed to process particle segmentation data and correlate morphological descriptors with catalytic performance, enabling quantitative assessment of particle size distributions, skewness, kurtosis, and aggregation behavior. These data-driven insights corroborate the experimentally observed structure-activity relationships, linking controlled nucleation under microwave irradiation to enhanced catalytic efficiency. The results establish amorphous Nb₂O₅ as a cost-effective and sustainable catalyst for on-demand hydrogen generation and highlight pressureless microwave synthesis combined with machine learning as a powerful framework for rational catalyst design.