Exfoliated Cobalt-Doped Manganese Oxide Nanosheets: An Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction in an Alkaline Medium

Abstract

Endeavors toward designing and developing an easy-to-use, durable, effective, and non-noble-metal-based electrocatalyst for hydrogen evolution reaction (HER) are still ongoing. Two-dimensional (2D) transition metal oxide nanosheets (NSs) are now at the forefront of the race due to their huge lateral size compared to thickness owing to unique electronic and physicochemical properties compared to their bulk material and edge atom sites offering catalytic centers for HER. In this report, Co-doped MnO 2 [Mn 1−x Co x O 2 , x = 0.0−0.5] NSs were synthesized through chemical exfoliation. The electrochemical performance of different degrees of Co-doped MnO 2 NS samples toward HER was assessed in 1 M KOH solution by drop casting the NS dispersion on Ti foil. The superiority toward HER of exfoliated samples of any degree of Co doping in MnO 2 (x = 0.0−0.5) NSs compared to their bulk samples was observed. Within exfoliated samples, 20% Co-doped MnO 2 showed relatively better performance compared to other compositions with an overpotential of 218 mV at a 10 mA cm −2 current density and a Tafel slope of 122 mV dec −1 . Not only does it offer a reasonably low overpotential for HER but also provides a stable current density of ∼10 mA cm −2 for ∼12 h at the given overpotential. The substantially enhanced performance by 20% Co-doped MnO 2 NSs can be attributed to larger oxygen vacancies, preferential adsorption of water molecules, higher electrical conductivity, and fast charge transfer rate. Interestingly, the electrode preparation using this Co-doped MnO 2 NS dispersion adopted here does not involve usage of either any binder or conductive carbon, and the overpotential observed is either quite low or comparable to the state-of-the-art catalysts known of similar type in an alkaline medium. This study offers a highly potential and cost-effective scalable two-dimensional non-noble-metal-based electrocatalyst for HER in practical application.