Ni_xRh_1-xO_y composite nanofibres as highly efficient and robust oxygen evolution electrocatalysts

Metal oxide composite nanofibres consisting of Ni and Rh (denoted as Ni_xRh_1−xO_y, 0 < x < 1) were synthesised using a simple electrospinning and post-calcination process. The electrospun Ni_xRh_1−xO_y composite nanofibres showed various morphologies and crystallinities depending on the relative molar ratio of Ni to Rh. While Ni_xRh_1−xO_y 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, Ni_0.57Rh_0.43O_y, 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, Ni_xRh_1−xO_y (0.27 ≤ x ≤ 0.39) possessed a rugged nanofibre structure consisting of crystalline RhO_y and NiO. Electrocatalytic activity measurements of the electrospun composite nanofibres, when used for an oxygen evolution reaction (OER), demonstrated that the Ni_0.77Rh_0.23O_y nanofibres were the most effective in a 1 M NaOH aqueous solution. Ni_0.77Rh_0.23O_y, 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 Ni_0.77Rh_0.23O_y could be reasonably ascribed to the unique morphological and crystalline characteristics as well as the synergistic effect of mixed Ni and Rh oxides.