High pressure forms of aqueous carbon*

The chemistry of carbon in aqueous fluids at extreme pressure and temperature conditions is of great importance to Earth's deep carbon cycle. A major obstacle to understanding deep carbon transport is the lack of knowledge of carbon reactions in water at the extreme conditions found in Earth's deep interior. Here, by applying first-principles molecular dynamics simulations, we predicted a few interesting and important carbon reactions in supercritical water, which are dramatically different from what we know at close to ambient conditions. We found that carbonic acid can be the most abundant carbon species in aqueous CO₂ solutions at ∼10 GPa and 1000 K. In CO₂-rich solutions, significant proton transfer between carbonic acid molecules and bicarbonate ions may enhance the conductivity of solutions. In less oxidized solutions, the reactions of carbon monoxide may participate in the diamond formation.
N. Stolte and D. Pan, J. Phys. Chem. Lett. 10, 5135 (2019)