A solar-driven CO₂ reduction (CO₂R) device that consists of a tandem InGaP/GaAs/TiO₂/Ni photoanode in 1.0 M KOH for oxygen evolution reaction (OER), a Pd/C nanoparticles dark cathode in bicarbonate electrolyte at pH=8.0 for CO₂R reaction and a bipolar membrane exhibited a solar-to-fuel (STF) conversion efficiency of 10%. The Pd/C nanoparticles showed low overpotential (< 100 mV) and high faradic efficiency (> 94%) for CO₂ reduction to formate at 8.5 mA cm^-2. The bipolar membrane exhibited low formate crossover and high transference number for proton and hydroxide at the steady-state pH gradient. The effective coupling between two different electrolytes that optimize the performance of CO₂R reaction and OER provides new cell design spaces for efficient solar-fuel generation.