In addition, a CV experiment was carried out in which a Ni-OMebpy mixture (1:2, Ni:OMebpy) was reduced alone and in the presence of 4-bromobenzotrifluoride or 4iodobenzotrifluoride (See SI, Fig. ). In the presence of either aryl halide, the quasi-reversible reduction becomes irreversible with disappearance of the oxidation waves, consistent with oxidative addition. A greater catalytic current is observed for the aryl iodide as compared with the aryl bromide, suggesting that oxidative addition occurs at a faster rate with that type of substrate, consistent with known OA rates at Ni(I). Photocatalyst Regeneration Through Bromide Oxidation. The reaction scheme described above in which iodide liberated through oxidative addition regenerates Ir(III) from Ir(IV) provokes the question as to whether the same chemistry might occur with bromide (either introduced with the NiBr2 source or generated via oxidative addition of an aryl bromide). By CV, the reaction appears to be feasible (See SI, Table ), although the overpotential is significantly less as compared with iodide. To investigate this potential pathway directly, an experiment was designed in which electrochemically generated Ir(IV) was exposed to bromide after the potentiostat was turned off and the kinetics were followed by UV-vis (Fig. ). Importantly, bromide reacted with Ir(IV) as evidenced by a significantly faster decrease in the signal at λprobe = 600 nm as compared with a control run where DMF was injected, causing only a dilution effect. Thus, bromide might serve as a redox mediator to accelerate PC turnover, with the resulting bromine radical deactivating the active Ni(I) complex to form a Ni(II) bromide complex. Other deleterious termination pathways for the bromine radical are