First-principles studies of oxidized carbon in water under extreme conditions

The properties of oxidized carbon and water mixtures at high pressure (HP) and high temperature (HT) are of great importance to the deep carbon cycle, which involves more than 90% of Earth's carbon and substantially impacts the carbon budget near Earth's surface. We studied CO₂ in supercritical water up to ~13 GPa and 1400 K using ab initio molecular dynamics, and found that while the major form of dissolved carbon is CO₂(aq) at ambient conditions, carbonic acid (H₂CO₃(aq)) can be more abundant than CO₂(aq) at HP-HT when the total mole fraction of carbon is below 40%. We investigated the aqueous reaction mechanisms of H₂CO₃(aq) formation and dissociation at HP-HT at the molecular scale. We will discuss the possible P-T range for the stability of H₂CO₃(aq). Our study suggests that H₂CO₃(aq) may be an important carbon transport host in the deep carbon cycle.