Design of a high-efficiency magnetically separable Fe₃O₄@Al₂O₃/Co-Cs catalyst for sustainable hydrogen generation via NaBH₄ hydrolysis: experimental and DFT insights

We report the first successful synthesis of a novel magnetically recoverable nanocatalyst, Fe₃O₄@Al₂O₃/Co–Cs, incorporating cesium (Cs) as a co-catalytic promoter for efficient and sustainable hydrogen generation via NaBH₄ hydrolysis. In this system, magnetite (Fe₃O₄) serves as a magnetic core, enabling facile separation and recyclability, whereas the Al₂O₃ shell enhances thermal stability, structural integrity, and active-site dispersion. Cobalt (Co) acts as the primary active metal, whereas Cs is introduced here for the first time in NaBH₄ hydrolysis as an electronic promoter, significantly enhancing electron transfer and accelerating the hydrogen generation rate (HGR). Comprehensive characterization using FTIR, XRD, FE-SEM/EDX, and BET analyses confirmed the successful formation of a hierarchical core–shell structure. FE-SEM images revealed a flower-like morphology composed of aggregated nanosheets and nanoparticles that promoted efficient mass transfer and gas diffusion. Catalytic performance tests conducted at 30 °C demonstrated a high hydrogen generation rate of 17.24 L g⁻¹ min⁻¹. The apparent activation energy was determined to be 27.18 kJ mol⁻¹, indicating favorable reaction kinetics under mild conditions. Thermodynamic analysis revealed a low enthalpy of adsorption (ΔH_ads = 35.66 ± 0.01 kJ mol⁻¹) and a small entropy change (ΔS° = 0.09022 ± 0.01 kJ mol⁻¹ K⁻¹), suggesting favorable interactions between the reactants and catalyst surface. Density functional theory (DFT) calculations further confirmed that the Fe₃O₄@Al₂O₃/Co–Cs system exhibited enhanced adsorption strength and reduced activation barriers, facilitating NaBH₄ hydrolysis through efficient charge transfer, intermediate stabilization, and synergistic catalytic effects. Overall, this study highlights the novel role of cesium as an alkali metal promoter in NaBH₄ hydrolysis, opening new opportunities for the design of advanced non-noble metal catalysts for hydrogen generation.