Regulating electronic structure by Mn doping for nickel cobalt hydroxide nanosheets/carbon nanotube to promote oxygen evolution reaction and oxidation of urea and hydrazine

Abstract

Electrocatalytic water splitting is one of the direct and efficient means to yield high-purity hydrogen, but it still exists some challenges in addition to the sluggish anodic oxygen evolution reaction (OER). Constructing highly-efficient electrocatalysts with superior properties plays an essential role in industrial hydrogen production. In this work, a novel electrocatalyst with a distinctive three-dimensional (3D) structure is constructed by intertwining two-dimensional (2D) hexagonal NiCo hydroxide nanosheets (NiCo HNS) with one-dimensional (1D) carbon nanotubes (CNTs). The strategy of elemental doping engineering is employed to further enhance the catalytic performance. The as-fabricated composite of Mn-doped nickel cobalt hydroxide nanosheets intertwined with CNTs (1.5Mn-NiCo HNS/CNT) delivers superior OER electrocatalytic performance, which requires an overpotential of only 239 mV to achieve the current density of 10 mA cm−2 in 1 M KOH. Compared to NiCo HNS/CNT, the 1.5Mn-NiCo HNS/CNT electrocatalyst exhibits characteristics of improved electrical conductivity, larger electrochemical active surface area (ECSA), and faster reaction kinetics due to Mn doping. Density functional theory (DFT) calculations revealed that the adsorption of OH– during the first step of OER process was the potential determining step for the Mn substituted Co sites, and the Mn substituted Co sites were the optimum reactive sites that determined the OER performance of the 1.5Mn-NiCo HNS/CNT. Mn doping was proved beneficial to optimize the reaction path and decrease the reaction kinetics energy barrier. The addition of urea or hydrazine into the electrolyte directly decreases the energy consumption and realize their decomposition as pollutants in industrial and agricultural wastewater.