Water Management Using Massively Produced Calcium Carbonate for Pilot-Scale CO₂ Electrolysis

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 (CaCO₃), an earth-abundant mineral. Using in situ spectroscopy and theoretical simulations, we reveal that the uniquely hydrophilic surface of CaCO₃ selectively enriches and stabilizes the more mobile and reactive liquid-like water molecules (2-HB·H₂O), thereby establishing an efficient proton highway near the electrode. This enables metal-loaded CaCO₃ (M/CaCO₃, 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 CO₂ conversion to C₂₊ (FE_C2+ 77.97%) or syngas (19 L h^{- 1}; the CO/H₂ ratio ∼2) in a 100 cm² electrolyzer stack. This work establishes a general paradigm for using natural minerals to manipulate interfacial water dynamics for industrial electrocatalysis.