Electrolyte pH modulation for efficient and durable electrochemical cement clinker precursor production†

Abstract

Cement production is carbon intensive and accounts for 7–8% of global CO₂ emissions. Deep cement decarbonization can be achieved if limestone calcination is replaced with an ambient-temperature electrochemical process. A big challenge of this process is the significant deposition of the Ca(OH)₂ product on the membrane, causing unacceptable operational durability and energy efficiency. To address this issue, we designed a two-chamber membrane-based cement clinker precursor electrolyzer. The electrolyte pH modulation and its effect on decarbonization, precipitation, and cell voltage are investigated. We reveal a thin Ca(OH)₂ layer on the anode side of the membrane under fast decarbonization kinetics (99% current efficiency) at a pH of 5.1, increasing the cell voltage by 50%. A periodic pH change using intermittent stirring ensures a relatively constant voltage level with a sacrifice of ∼3% decarbonization efficiency. Membrane clogging is extremely significant in the cathode chamber due to the extreme pH environment (12.4), causing an inferior production rate of Ca(OH)₂ (59% of the theoretical limit). Introducing Ca²⁺ into the catholyte leads to a much lower pH (11.8) and a clean membrane throughout the electrolysis, increasing the current efficiency for Ca(OH)₂ production to 84%. Our work demonstrates a viable approach for efficient and durable production of electrochemical cement clinker precursors.