NixRh1-xOy composite nanofibres as highly efficient and robust oxygen evolution electrocatalysts

Abstract

Metal oxide composite nanofibres consisting of Ni and Rh (denoted as NixRh1−xOy, 0 < x < 1) were synthesised using a simple electrospinning and post-calcination process. The electrospun NixRh1−xOy composite nanofibres showed various morphologies and crystallinities depending on the relative molar ratio of Ni to Rh. While NixRh1−xOy with a high Ni content (0.67 ≤ x ≤ 0.83) showed the typical structure of nanotube-like main backbones decorated with flake-sprouts and consisted of amorphous Rh oxide and crystalline NiO, Ni0.57Rh0.43Oy, with its more moderate Ni content, had a smooth nanofibre structure, which was also composed of amorphous Rh oxide and crystalline NiO. On the other hand, NixRh1−xOy (0.27 ≤ x ≤ 0.39) possessed a rugged nanofibre structure consisting of crystalline RhOy and NiO. Electrocatalytic activity measurements of the electrospun composite nanofibres, when used for an oxygen evolution reaction (OER), demonstrated that the Ni0.77Rh0.23Oy nanofibres were the most effective in a 1 M NaOH aqueous solution. Ni0.77Rh0.23Oy, with a high content of relatively inexpensive Ni, presented OER activity and stability that were superior even to those of commercial iridium, and can be considered as a promising cost-effective catalyst. In our study, the high OER activity of Ni0.77Rh0.23Oy could be reasonably ascribed to the unique morphological and crystalline characteristics as well as the synergistic effect of mixed Ni and Rh oxides. © 2020 Elsevier B.V.