Temperature-controlled fabrication of Co-Fe-based nanoframes for efficient oxygen evolution

Transition metal phosphides (TMPs) have emerged as promising electrocatalysts to enhance the slow kinetic process of oxygen evolution reaction (OER). Framelike hollow nanostructures (nanoframes, NFs) provide the open structure with more accessible active sites and sufficient channels into the interior volume. Here, we report the fabrication of bimetallic Co-Fe phosphide NFs (Co-Fe-P NFs) via an intriguing temperature-controlled strategy for the preparation of precursors followed by phosphidation. The precursors, Co-Fe Prussian blue analogues (Co-Fe PBAs) are prepared by a precipitation method with Co2+ and [Fe(CN)6]3−, which experience a structural conversion from nanocubes to NFs by increasing the aging temperature from 5 to 35°C. The experimental results indicate that this conversion is attributable to the preferentially epitaxial growth on the edges and corners of nanocubes, triggered by intramolecular electron transfer at an elevated aging temperature. The as-prepared Co-Fe-P NFs catalyst shows remarkable catalytic activity toward OER with a low overpotential of 276 mV to obtain a current density of 10 mA cm−2, which is superior to the reference samples (Co-Fe-P nanocubes) and most of the recently reported TMPs-based electrocatalysts. The synthetic strategy can be extended to fabricate Co-Fe dichalcogenide NFs, thereby holding a great promise for the broad applications in energy storage and conversion systems.