Bifunctional Marsilea minuta Biochar for Sustainable Hydrogen and Oxygen Production

Abstract The high cost, scarcity, and limited stability of noble-metal-based electrocatalysts, such as platinum and rhodium, have motivated the search for more abundant, sustainable, and economically viable alternative materials for water electrolysis. In this context, biochar obtained from plant residues stands out as a promising carbonaceous material for the development of efficient electrocatalysts with low environmental impact. In this work, an electrocatalyst based on biochar derived from the aquatic plant Marsilea minuta was developed and evaluated for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Structural and chemical characterization revealed an amorphous, porous structure and the presence of oxygen- and nitrogen-containing functional groups, including carboxylic acids, and pyridinic N moieties, which may serve as active sites favorable for electrocatalytic reactions. Electrochemical analyses performed using a glassy carbon electrode modified with the material demonstrated significant activity toward both HER and OER, with low overpotentials of −0.19 and 0.36 V vs. the reversible hydrogen electrode (RHE), respectively, required to reach current densities of 10 mA cm–2, and Tafel slopes consistent with favorable reaction kinetics. Electrochemical stability was confirmed by chronopotentiometric measurements, highlighting the potential of the biochar (BMQ) as a low-cost, low environmental impact, bifunctional electrocatalyst.