Specifically, E 0 substrate > 𝐸 CO 2 /CO 2 .- 0 ensures that SET from CO2 •-to the aryl halide substrate is thermodynamically allowed, while E 0 product < 𝐸 CO 2 /CO 2 .- 0 dictates that the product is stable towards further SET in the presence of CO2 •-. For example, the mediated oxidative reduction of bromobenzene in CPE does not occur as E 0 for this substrate is negative of E 0 (CO2 •-/CO2), Figure . This result is consistent with the formation of bromobenzene upon mediated oxidative reduction of each of the three di-bromobenzene derivatives, Figure .