Electrochemical Deposition of Fe/FeOOH Nanoforest Catalyst: Growth Mechanism and Structural Self-Optimization

Hierarchical nanostructures provide a platform to build functional materials. Here, we report a one-step electrochemical deposition of Fe/FeOOH nanoforests, where tree-like three-dimensional (3D) architectures comprising one-dimensional (1D) metallic Fe branches and two-dimensional (2D) FeOOH leaves are uniformly and densely grown on the substrate to form a forest-like assembly. Detailed microscopic observations reveal that the hierarchical structure is organized through the multidimensional oriented attachment of FeOOH nuclei, followed by the internal reduction to Fe nanowires. The coupling between the catalytically active FeOOH leaves and the electrically conductive Fe nanowires provides superior catalytic activity and durability for the oxygen evolution reaction (OER). Furthermore, the excess FeOOH layer is selectively eliminated during OER operation, leading to self-optimization of the catalytic activity.