Formic acid and formate salts are key intermediates along the pathways for CO₂ utilization and hydrogen storage. Herein we report a highly efficient multiphase catalytic system utilizing a ruthenium PNP pincer catalyst for converting supersaturated bicarbonate solutions and slurries to aqueous formate solutions up to 12 M in molarity. The biphasic catalytic system delivers turnover frequencies up to 73 000 h⁻¹ and remains stable for up to 474 000 turnovers once reaction conditions are optimized.