Electrochemical CO ₂ Mineralization and H ₂ Generation from Steel and Coal Waste

High Resolution Image Download MS PowerPoint Slide We introduce a process that electrochemically couples CO 2 capture and mineralization (CCM) with water electrolysis (WE). Leveraging the exothermicity of CO 2 mineralization to sustain a reverse pH gradient, this approach lowers the potential required for WE by up to 0.39 V. Demonstration in a three-chamber reactor yields a steady-state pH gradient of 4.4, enabling WE at an onset of 1.30 V and Faradaic efficiency for CO 2 fixation of 93%, corresponding to a net energy cost of < 0.5 kWh (kg CO 2 ) –1 . Abundant waste streams, including steel slag and coal ash, serve as CO 2 sorbents, resulting in waste valorization to synthetic calcite. Accounting for the value of calcite, estimated H 2 production costs are < 1 USD kg –1 . Because CO 2 fixation exceeds grid emissions for the equivalent electrical energy consumption, this process produces carbon-negative H 2 using immediately available electricity. At scale, this process has the potential to mitigate > 500 Mt CO 2 emissions annually.