Importance of the catalyst–water Coulomb interaction for oxygen reduction reaction kinetics

Abstract

We identify an important new factor affecting oxygen reduction reaction (ORR) kinetics (i.e., the catalyst–water Coulomb interaction). The stronger Coulomb interaction leads to a stronger water wall at the catalyst/water interface and thus renders the contact between catalytic sites and O2 molecules more difficult, thereby resulting in more sluggish ORR kinetics. The difference in ORR kinetics can reach 10,000-fold between the catalyst with the strong Coulomb interaction and that with the weak Coulomb interaction. Additionally, we reveal an important (yet previously overlooked) prerequisite for a material to be an ORR electrocatalyst comparable to Pt: the atomic charge of catalytic sites should be between −1.0 e and 0.9 e (to circumvent the strong Coulomb interaction). This finding well explains recent experimental results showing that transition metal oxides based on Fe, Y, Ni, Mn, and La have intrinsically limited ORR kinetics (Nat. Catal., 2021, 4, 463–468). The successful explanation further substantiates the plausibility of the finding. Furthermore, we demonstrate that the catalyst–water Coulomb interaction also has a similar effect on the other electrocatalytic reactions consuming small nonpolar molecules, such as the hydrogen oxidation reaction and the nitrogen reduction reaction.