Morphology Mapping of Nickel-Cobalt/Carbonate Hydroxide Nanostructures on Carbon Fibre Electrodes for Oxygen Evolution Reaction

The performance of self-supported electrodes is governed not only by composition, but also by the nanoscale structure through which the active material interfaces with the current collector and electrolyte. Here, a hydrothermal route on carbon fibre paper is used as a model platform to prepare nickel-cobalt hydroxide/carbonate-hydroxide nanostructures across a controlled composition series. Rather than introducing new catalyst chemistry, this work establishes an image-based morphology map linking mesoscale structural parameters to the apparent oxygen evolution reaction (OER) response. Scanning electron microscopy reveals a systematic evolution from Co-rich nanofibre coatings to Ni-rich nanoplate architectures. The nanostructures are quantified through the fibre diameter, D , and the nanoplate thickness and length, t and L . These parameters capture trends that nominal composition alone does not explain: the apparent Tafel slope decreases as the fibre diameter is reduced and the fibrous morphology is replaced by plates, while the apparent charge-transfer resistance follows the evolution of the nanoplate dimensions. The 1:1 Ni:Co electrode deviates from a simple composition-based trend, being consistent with its mixed fibre/plate architecture and comparatively large plate dimensions. The best Ni-rich electrode reaches an overpotential of 365 mV at 10 mAcm -2 after conditioning and operates at 20 mAcm -2 for 50 h with negligible morphological degradation. These results provide a practical morphology design rule for carbon-supported Ni-Co hydroxide-derived electrodes.