Facile synthesis and self-assembling of transition metal phosphide nanosheets to microspheres as a high-performance electrocatalyst for full water splitting

The development of noble-metal-free electrocatalysts with enhanced active sites is of great significance for the production of renewable energy on large scale. Ultrathin transition metal compounds (e.g., phosphides and sulfides) have unique structural features but their stability and electroactivity must still be improved for practical applications. We propose a new strategy to synthesis ultrathin sheets of Ni-Cu-Co transition metals on porous nickel and self-assemble them into yam-shaped microspheres. Enhance catalytic activity and stability are then attained by thermochemical phosphorization without morphological modifications. We employed various analytical techniques including XRD, SEM, TEM, and in-depth electrochemical analysis for materials characterizations. It is shown that ultrathin nanosheets with a thickness of few nanometers and lateral dimensions of a few hundred nanometers are formed and assembled to yarn-shape microspheres with an average diameter of similar to 7 mu m. To demonstrate the practical application of the developed nanostructured compounds, their bifunctional electroactivity toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline solution (2.0 M NaOH) is demonstrated. On the best practice, co-alloying of Ni with Cu and Co with a ratio of Cu/Co=2.5 enhances the catalytic activity by similar to 30%. Further improvement (by about 55%) is attained by thermochemical phosphorization. The electrocatalyst merely required an overpotential of 175 mV (for HER) and 265 mV (for OER) to deliver a current density of 10 mA cm(-2). No changes in the current density were observed after a long-time at higher current densities (-88 and +39 mA cm(-2)) showing the high stability of the catalyst in the alkaline solution. The mechanism of improved performance is elaborated and ascribed to the engineered morphology of the nanostructures having many active sites at the surface to promote the Volmer reaction combined with accelerated electrolyte diffusion, rapid charge transport, and gas bubbles detachment at the interface with the electrolyte. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study focuses on the development of noble-metal-free electrocatalysts with enhanced active sites by synthesizing ultrathin transition metal compounds and self-assembling them on porous nickel. The thermochemical phosphorization process further enhances the catalytic activity towards oxygen evolution reaction and hydrogen evolution reaction. This nanostructured compound demonstrates high stability and efficiency in alkaline solution for renewable energy production.