Non-Covalent Assembly of Proton Donors and p-Benzoquinone Anions for Co-Electrocatalytic Reduction of Dioxygen
With weak acids (AH) at high concentrations, potential inversion can occur due to favorable hydrogen-bonding interactions with the intermediate monoanion [BQ(AH)m]•–. The solvation shell created by these interactions can mediate a proton-coupled electron transfer at more positive potentials, resulting in an overall two electron reduction ([BQ(AH)m]•– + nAH + e– ⇌ [HBQ(AH)(m+n)-1(A)]2–). Here we show that the resultant hydrogen-bonded [HBQ]– adduct mediates the transfer of electrons and the proton donor 2,2,2-trifluoroethanol (TFEOH) to a Mn-based complex during the electrocatalytic reduction of dioxygen (O2). The Mn electrocatalyst is selective for H2O2 with only TFEOH and O2 present, however, with BQ present under otherwise analogous conditions, an electrogenerated [HBQ(AH)4(A)]2– adduct (where AH = TFEOH) alters product selectivity to 96(±0.5)% H2O in a co-electrocatalytic fashion. These results suggest that hydrogen-bonded [HBQ]– dianions can function in an analogous co-electrocatalytic manner to H2Q.