Ultrasmooth and Thin Pheomelanin-like Film as a Metal-Free Electrocatalytic Enhancer

Abstract

This study explores a bioinspired approach to enhance electrocatalytic oxygen evolution reaction (OER) performance by employing a pheomelanin-like thin film. Inspired by the complex chemistry of natural pigments, we developed an ultrasmooth and exceptionally thin organic coating by introducing cysteine derivatives into dopamine-based solutions. The resulting film, approximately 2 nm thick, forms conformal layers on conventional RuO₂ electrocatalysts and significantly reduces the overpotential required for OER. Specifically, coatings with cysteine methyl ester (CME) or cysteine ethyl ester (CEE) achieved overpotential reductions of up to 34 mV at 10 mA·cm^-2 compared to pristine RuO₂. Beyond improved catalytic performance, the films exhibited unique deposition kinetics characterized by an autocatalytic “bursting” behavior, highlighting the emergent properties of the system. Our findings underscore the potential of bioinspired organic materials to modulate electrocatalytic interfaces, offering new strategies for the rational design of hybrid catalytic systems in energy conversion technologies.