Introduction to CO2 Electroreduction

1.1 CHEMICAL AND PHYSICAL PROPERTIES OF CO₂

Carbon dioxide (CO₂) (mole weight 44.0) is a linear molecular (O=C=O), in which two oxygen (O) atoms are each covalently double bonded to a single carbon (C) atom. With an average C=O bond energy E_C=O [=187 (2 × 93.5) kcal/mole] being much higher than E_O=O [=116 (2 × 58)] and E_C=C [=145 (2 × 72.5)], CO₂ is rather chemically stable unless chemically,^1–10 electrocatalytically, and photocatalytically^11–19 treated under vigorous conditions. It usually exists as a colorless and odorless gas in air with a mean atmospheric concentration of 0.039% (v/v), and is well known as one of the most notorious greenhouse gases. It forms solid dry ice at –78.5°C and it partially dissolves and is even dissociated in water (1.45 g/L at 25°C, 100 kPa).