2. Possible 2H+/2e– Paths for Reducing CO2 to CO by Catalyst 1 or 2 .

a Note that the bold Ni in the scheme represents either NiN4- or NiN3S-coordinated TPP. Dashed lines refer to CPET. The initial species for NiN4-TPP is [Ni]0, while for NiN3S-TPP, it is [Ni–Cl]0.