Swelling-Assisted Electrochemical Activation of Bio-Derived Carbon-Based Hydrogel as a Binder-Free and High Stability Electrocatalyst for HER and ORR

Abstract Designing efficient and durable metal-free electrocatalysts is of great importance for emerging electrochemical energy conversion technologies. Herein, a binder-free and high-stability electrocatalyst, quince seed mucilage−graphene oxide (QG) hydrogel, is investigated for the oxygen reduction reaction (ORR) in alkaline media and the hydrogen evolution reaction (HER) in acidic electrolyte. The hydrogel exploits the viscoelasticity and shear-thinning property of the biopolymer matrix with the functional properties of QG for electrode coating and electrolyte-triggered interfacial behavior. Rheological characterization indicates a mechanically stable, shear-thinning network. Electrochemical measurements including linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, rotating ring-disk electrode analysis, Tafel analysis, and Koutecký−Levich modeling are used to determine catalytic activity and reaction pathways. Upon exposure to the electrolyte, the electrochemical response is modified with changes in current density, charge-transfer resistance, and double-layer capacitance in agreement with progressive activation of the electrode and enhanced interfacial accessibility assisted by swelling. The 4-electron ORR pathway with a low yield of peroxide and faradic efficiency is further assessed by RRDE measurements and Koutecký−Levich analysis. HER analysis reveals lower overpotential after swelling, lower charge-transfer resistance, and better reaction kinetics. The results demonstrate that the QG hydrogel is a promising biopolymer-based platform for studying the relationship between rheological properties, hydration, and electrocatalytic performance and provide a potential strategy for developing more sustainable electrode materials without the intentional addition of catalytic metals.