Fractal-Structured Electrode Based on rGO-Supported Mixed Metal Oxide for Enhanced Oxygen Evolution Electrocatalysis

Abstract Inspired by the excellent transport phenomenon of the natural leaf venation assembly, nano/microstructure fractal-patterned electrodes were biomimicked, exhibiting a multipath charge-directing mechanism that enhances charge transport and catalytic activity for water oxidation. Fractal-like architecture of rGO-supported CoMnOx electrocatalysts fabricated using a manually lifted Hele-Shaw cell shows significantly lower overpotential (261 mV) as compared to their nonfractal structure (304 mV) at 10 mA cm–2. The results were supported by the Tafel slope (76 mV/dec), reduced charge transfer resistance (5 Ω) which is almost half as compared to their nonfractal (9.8 Ω), and a higher electroactive surface area (ECSA) of 2.05 cm2, evidencing significant exposure of surface area and offering more access to active sites. The fractal structure shows a high fractal dimension (Df = 2.96), indicating a rough and porous surface. In-situ Raman spectroscopy confirms that the fractal pattern facilitates the formation of catalytically active oxyhydroxide species at a lower potential (1.49 V vs RHE) compared to its nonfractal counterpart. Further, quantitative analysis of venation parameters shows that total vein length increases linearly with the increasing perimeter, while vein density decreases, which is in good agreement with the natural leaf vein phenomenon. The significant advancement is attributed to the vein-like fractal architecture, which provides numerous routes and acts as a charge-directing agent and promotes rapid charge transport; increased active sites; enhanced active surface area; and accelerated electrochemical reconstruction. To the best of our knowledge, this is the first report that investigates transition metal-based fractal-like electrodes fabricated through a hand-lifted Hele-Shaw method for enhancing the oxygen evolution reaction.