Electrocatalytic oxygen reduction with cobalt corroles bearing cationic substituents.

Recent decades have seen increasing interest in developing highly active and selective electrocatalysts for the oxygen reduction reaction (ORR). The active site environment of cytochrome c oxidases (CcOs), including electrostatic and hydrogen-bonding interactions, plays an important role in promoting the selective conversion of dioxygen to water. Herein, we report the synthesis of three CoIII corroles, namely 1 (with a 10-phenyl ortho-trimethylammonium cationic group), 2 (with a 10-phenyl ortho-dimethylamine group) and 3 (with a 10-phenyl para-trimethylammonium cationic group) as well as their electrocatalytic ORR activities in both acidic and neutral solutions. We discovered that 1 is much more active and selective than 2 and 3 for the electrocatalytic four-electron ORR. Importantly, 1 showed ORR activities with half-wave potentials at E1/2 = 0.75 V versus RHE in 0.5 M H2SO4 solutions and at E1/2 = 0.70 V versus RHE in neutral 0.1 M phosphate buffer solutions. This work is significant for outlining a strategy to increase both the activity and selectivity of metal corroles for the electrocatalytic ORR by introducing cationic units.

Effect of Proton Transfer on Electrocatalytic Water Oxidation by Manganese Phosphates.

The effect of proton transfer on water oxidation has hardly been measurably established in heterogeneous electrocatalysts. Herein, two isomorphous manganese phosphates (NH4 MnPO4 ⋅ H2 O and KMnPO4 ⋅ H2 O) were designed to form an ideal platform to study the effect of proton transfer on water oxidation. The hydrogen-bonding network in NH4 MnPO4 ⋅ H2 O has been proven to be solely responsible for its better activity. The differences of the proton transfer kinetics in the two materials indicate a fast proton hopping transfer process with a low activation energy in NH4 MnPO4 ⋅ H2 O. In addition, the hydrogen-bonding network can effectively promote the proton transfer between adjacent Mn sites and further stabilize the MnIII -OH intermediates. The faster proton transfer results in a higher proportion of zeroth-order in [H+ ] for OER. Thus, proton transfer-affected electrocatalytic water oxidation has been measurably observed to bring detailed insights into the mechanism of water oxidation.