Synthesis of sulfur-encapsulated mullite structure Bi⁰/Fe⁰-Rich Bi₂Fe₄O_9−x framework by advanced probe sonic approach applied for augmented electroactive hydrogen production, storage and photoactive degradation studies

A new series of dual Bi⁰/Fe⁰-rich in sulfur-encapsulated BFNPs (SBFNPs-framework) with a sulfur content ranging from 1.0% to 3.0% were prepared using an advanced probe-sonic approach. The SBFNPs-framework with a sulfur content of 2.0% exhibited a maximum methylene-blue (MB) photo-degradability of 84.20% at 120 min of visible-light exposure. The MB degradation rate of the SBFNPs-framework (0.00839 min⁻¹) was faster than that of pure-BFNPs (0.00308 min⁻¹). Furthermore, the electro-catalyst of SBFNPs-framework demonstrated remarkable hydrogen-production activity, as indicated by a low over-potential (204 mV), a small Tafel-slope (69 mV/dec), a higher double-layer-capacitance (142.0 mF/cm²), a larger electro-chemically-active-surface-area (40.6 cm²), a plentiful presence of catalytic-active-sites (5.65 ×10⁻⁷ mol/cm²), and excellent stability, respectively. Also, the hydrogen-storage capacity of the SBFNPs-framework exhibited a maximum discharge capacity of 717.35 mAhg⁻¹ and a hydrogen-storage capacity of 2.66 wt% at a 2.0% sulfur content. These findings have great potential implications for future energy storage and environmental applications.