Water Management Using Massively Produced Calcium Carbonate for Pilot‐Scale CO 2 Electrolysis

ABSTRACT The performance of scalable, catholyte‐free membrane electrode assemblies (MEAs) is restricted by insufficient interfacial water and proton supply. Here, we present a general strategy for constructing an ideal proton‐feeding microenvironment based on calcium carbonate (CaCO 3 ), an earth‐abundant mineral. Using in situ spectroscopy and theoretical simulations, we reveal that the uniquely hydrophilic surface of CaCO 3 selectively enriches and stabilizes the more mobile and reactive liquid‐like water molecules (2‐HB·H 2 O), thereby establishing an efficient proton highway near the electrode. This enables metal‐loaded CaCO 3 (M/CaCO 3 , M = Zn, and Cu) catalysts to achieve exceptional performance at industrial‐relevant current densities. Crucially, we demonstrate that the catalyst can be synthesized on a kilogram scale directly from unpurified cement plant flue gas. This catalyst enables high‐rate CO 2 conversion to C 2+ (FE C2+ 77.97%) or syngas (19 L h − 1 ; the CO/H 2 ratio ∼2) in a 100 cm 2 electrolyzer stack. This work establishes a general paradigm for using natural minerals to manipulate interfacial water dynamics for industrial electrocatalysis.