Activated biochar derived from agricultural and aquatic waste biomass supported on stainless steel mesh for sustainable hydrogen evolution reaction in neutral media

Abstract

This work demonstrates a sustainable, scalable, and metal-free approach for converting agricultural waste and aquatic waste biomass (e.g., orange peel (OP), banana peel (BP), rice straw (RS), corn cob (CC), and water hyacinth (WH) into activated biochar while emphasizing the inherent kinetic limitations of hydrogen evolution (HER) in neutral electrolytes. A key challenge in HER under neutral conditions is the sluggish reaction kinetics caused by limited proton availability and slow water dissociation. Comprehensive characterization using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), and transmission electron microscopy (TEM) confirmed the formation of activated biochar with a layered carbon structure. Among the investigated materials, RS-, WH-, and CC-derived activated biochar exhibited improved HER performance, requiring overpotentials of 432-436 mV to achieve a current density of 10 mA cm⁻². Electrochemical analysis revealed reduced charge-transfer resistance and increased electrochemically active surface area, contributing to enhanced HER performance. Their corresponding Tafel slopes (323.2-352.4 mV dec⁻¹) are significantly lower than those of OP/SSM (533.5 mV dec⁻¹), BP/SSM (398.2 mV dec⁻¹), and commercial activated carbon as a control (651.67mV dec⁻¹). The enhanced performance is attributed to increased porosity, layered carbon morphology, the presence of intrinsic heteroatoms and mineral phases, improved electrochemically active surface area, and reduced charge-transfer resistance. This work demonstrates a sustainable and metal-free strategy for producing carbon-based electrocatalysts, while highlighting the limitations and challenges associated with HER in neutral electrolytes.