Biomimetic Cobalt Complex Stabilized by Hydrogel on High-Edge-Density Graphite for ORR and HER in Quiescent Solutions

Abstract

Biomimetic catalysts are increasingly relevant in energy conversion due to their ability to imitate the redox activity and selective catalytic efficiency of natural enzymes involved in key reactions such as the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). In this study, hydroxocobalamin acetate, a cobalt complex based on a corrin ring structure, analogue of vitamin B12 that mimics native active site of proteins, was immobilized on high-edge-density graphite electrodes (HEDGE). The exposed edge planes of HEDGE enhance electron transfer kinetics, providing a structurally favorable substrate for catalytic activity. The system was further encapsulated in an agarose hydrogel, which functions as a diffusion-regulating matrix, modulating gas and electrolyte permeability critical for sustained electrocatalytic performance in quiescent solutions. This configuration demonstrates dual catalytic functionality, efficiently facilitating ORR via selective molecular oxygen (O2) permeation and HER under mild conditions. Quiescent solutions, which mimic the diffusion-limited environments of natural enzymatic systems, present unique challenges such as gas bubble accumulation and restricted reactant transport. However, they also enable the investigation of intrinsic catalytic properties, offering biologically relevant insights into the system’s functionality. By emulating the microenvironmental conditions of natural enzymes, this hydrogel-based biomimetic system bridges the gap between biological principles and synthetic catalytic designs, providing a stable and efficient platform for electrocatalytic applications in energy conversion and storage technologies.