Morphology and phase transformation of α-MnO2/MnOOH modulated by N-CDs for efficient electrocatalytic oxygen evolution reaction in alkaline medium

Abstract Engineering non-precious electrocatalysts with excellent water oxidation performance is imperative for developing renewable and clean energy. Herein, we realize the simultaneous morphology and phase transformation from α-MnO2 nanorods, large-size MnOOH nanorods to MnOOH nanoparticles by adding different content of N-CDs in the synthesizing α-MnO2 process. Benefitting from the unique structures, synergistic effect between Mn-based oxides/oxyhydroxides and N-CDs, various active oxide species and large specific surface areas, the as-prepared Mn-based oxides/oxyhydroxides@CDs with different morphologies show excellent electrocatalytic performance for oxygen evolution reaction (OER) in 1.0 M KOH. Impressively, the large-size MnOOH@CDs0.2 display high electrocatalytic performance with the overpotential of 302 mV to reach to 10 mA cm−2 along with a Tafel slope of 51.3 mA dec−1. More importantly, by coupling the MnOOH@CDs0.2 with Pt/C for overall water splitting, a cell potential of merely 1.56 V is required to reach to 10 mA cm−2. Additionally, in the process of stability studies, the key role of the (111) crystal plane in the catalytic process is established. Meanwhile, the MnOOH@CDs0.2 also shows excellent stability for continuous 72 h chronopotentiometry test. The proposed strategy showed here represents a facile and suitable method for the simultaneous transformation of the morphology and phase of Mn-based oxides/oxyhydroxides with the assistance of N-CDs for efficient energy conversion.