Synergistically Enhanced Oxygen Evolution Catalysis with Surface Modified Halloysite Nanotube

Abstract

Synergistically increased oxygen evolution reaction (OER) of manganese oxide (MnO<sub>2</sub>) catalyst is introduced with surface-modified halloysite nanotube (Fe<sub>3</sub>O<sub>4</sub>-HNTs) structure. The flake shaped MnO<sub>2</sub> catalyst is attached on the nanotube template (Fe<sub>3</sub>O<sub>4</sub>-HNTs) by series of wet chemical and hydrothermal method. The strong interaction between MnO<sub>2</sub> and Fe<sub>3</sub>O<sub>4</sub>-HNTs maximized active surface area and inter-connectivity for festinate charge transfer reaction for OER. The synergistical effect between Fe<sub>3</sub>O<sub>4</sub> layer and MnO<sub>2</sub> catalyst enhance the Mn<sup>3+</sup>/Mn<sup>4+</sup> ratio by partial replacement of Mn ions with Fe. The relatively increased Mn<sup>3+/</sup>Mn<sup>4+</sup> ratio on MnO<sub>2</sub>@FHNTs induced <italic>σ</italic><italic><sup>*</sup></italic> orbital (e<sub>g</sub>) occupation close to single electron, improving the OER performances. The MnO<sub>2</sub>@FHNTs catalyst exhibited the reduced overpotential of 0.42 V (E <italic>vs</italic>. RHE) at 10 mA/cm<sup>2</sup> and Tafel slope of (99 mV/dec), compared with that of MnO<sub>2</sub> with unmodified HNTs (0.65 V, 219 mV/dec) and pristine MnO<sub>2</sub> (0.53 V, 205 mV/dec). The present study provides simple and innovative method to fabricate nano fiberized OER catalyst for a broad application of energy conversion and storage systems.