Abstract: Hydrogen energy, as a clean and efficient secondary energy source, plays an important role in achieving carbon neutrality. However, under alkaline conditions, the sluggish dissociation kinetics of water molecules severely limit the rate of the hydrogen evolution reaction (HER). Therefore, developing HER catalysts with high conductivity, high activity, and excellent stability is essential for efficient industrial water electrolysis. In this work, a mechanochemical strategy that synergistically combines cold-pressing with chemical reaction is proposed to break the room-temperature solubility limit of Pt in Ag, thereby constructing a self-supported cold-pressed Ag-Pt (P-AgPt) supersaturated surface alloy electrode. The resulting as-prepared P-AgPt electrode exhibits excellent performance in alkaline HER, exhibiting overpotentials of only 26 mV and 249 mV at current densities of 10 mA cm^-2 and 1 A cm^-2, respectively, and maintaining nearly no degradation after continuous operation at 0.5 A cm^-2 for 300 hours. Experimental and theoretical analyses reveal that the Ag-Pt dual-sites synergistically reduces the energy barrier for water dissociation and optimizes the hydrogen adsorption free energy, thus achieving a dynamic balance between water dissociation and hydrogen adsorption. This work demonstrates a reasonable strategy for breaking metal solubility limits at ambient conditions and provides an avenue towards high-activity, high-conductivity, and long-lived self-supported metallic electrodes for HER.