Concurrent H₂ Generation and Formate Production Assisted by CO₂ Absorption in One Electrolyzer

Electrolyzers coupling electrocatalytic hydrogen evolution with oxidation reactions of small organic molecules have the merits of reducing cell voltage and generating high-value products. Herein, an electrolyzer is designed and optimized that can simultaneously achieve efficient hydrogen generation at the cathode, CO₂ absorption by the catholyte, and methanol upgrading to formate at the anode. For these purposes, transition metal phosphides are used as the low-cost catalysts. The unique electrolyzer exhibits a low working voltage of 1.1 V at 10 mA cm⁻². Under optimal conditions, the Faraday efficiencies of hydrogen evolution and formic acid conversion reactions, which are the reaction products at the cathode and anode, respectively, are nearly 100% at various current densities from 10 to 400 mA cm⁻². Meanwhile, the CO₂ absorption rate is about twice that of the hydrogen generation rate, which is close to the theoretical value. An innovative and energy-efficient strategy is presented in this work to realize simultaneous hydrogen production and CO₂ capture based on low-cost catalyst materials.