<p>The high pseudocapacitance properties of mechanochemically synthesized BaSnF₄ in alkaline aqueous solutions are reported here for the first time. The structural and surface analysis confirms the presence of nanocrystalline tetragonal BaSnF₄ with a minor amount of the cubic phase and a thin surface layer rich in SnO₂, which promotes higher interfacial reactivity. The electrochemical properties of three electrolytes (NaOH, KOH, and Na₂SO₄) were examined, and for BaSnF₄, a prominent electrolyte-dependent charge-storage process was demonstrated. For BaSnF₄ in the alkaline solutions, the current response is high, and the specific capacitances reached the highest values of 402&#xa0;F g⁻¹ (in NaOH) and 350&#xa0;F g⁻¹ (in KOH) at a scan rate of 2 mV s⁻¹. The results from the Trasatti analysis proved the predominant contribution of the Faradic current to the total current in NaOH (83.6%) and in KOH (90.8%), thereby confirming the activation of the redox processes due to the interaction of the BaSnF₄ electrode with the negative species in the KOH solution. The specific charge capacities of the electrode are high, ranging from 24.4 to 26.3 mAh g⁻¹ at a current density of 0.5 Ag⁻¹. The Na₂SO₄ solution gives a typical EDLC process in the three electrolytes, with low specific capacitances of 19 to 71&#xa0;F g⁻¹ and specific charge capacities of 2.5 to 3.0 mAh g⁻¹, thereby confirming the absence of redox processes. The impedance response further validated the electrolyte dependence, showing the lowest charge-transfer resistance and most favorable phase behavior in NaOH. The electrode exhibits excellent cycling stability, retaining 99% and 86% of its capacitance over 5000 cycles in Na₂SO₄ and KOH electrolytes, respectively, whereas noticeable capacitance decay (57% retention) was observed in NaOH electrolyte. Post-cycling SEM and EDS elemental maps reveal particle fragmentation and loss of active material, which explain the capacitance decay. This study establishes BaSnF₄ as a promising fluorine-based pseudocapacitive electrode whose performance is significantly enhanced under strongly alkaline conditions.</p>