Turning Polluted Biomass Waste into Sustainable Carbon-Based Catalysts for Hydrogen Production via Water Electrolysis

The development of highly efficient, effective, and low-cost carbon-based catalysts for hydrogen production through water electrolysis represents a significant challenge in sustainable energy conversion. In this work, carbon materials derived from biomass waste, specifically a metal-polluted vegetal species (Spergularia rubra) from a former mining location, were used. Biomass was subjected to hydrothermal carbonization, producing hydrochar. The influence of both thermal and chemical post-treatment was studied in relation to hydrogen production efficiency. The thermal treatment was conducted at 300, 500, and 1000 °C, while the chemical precursors used were KOH and H₃PO₄. Additionally, these waste-derived carbon materials were compared with carbon Vulcan XC-72, a common reference material in these processes originated from fossil sources. Several electrochemical techniques were employed to evaluate and identify the most suitable sample for the hydrogen evolution reaction (HER). Additionally, physicochemical characterization analyses were conducted to gain a comprehensive understanding of the morphology, composition, and surface structure of the biomass-derived carbon materials, as well as to establish correlations with their electrochemical behavior toward the HER. The sample that demonstrated the most favorable performance was the one chemically activated with KOH, which exhibited an outstanding Tafel slope (147 mV/dec) and a low overpotential at 10 mA/cm² (−550 mV vs RHE) surpassing even the commercial Vulcan XC-72 sample. Furthermore, the chronoamperometry test showed a very stable performance for this sample. These results demonstrate that plant biomass waste containing metals presents a viable alternative to carbon blacks, commonly used as electrocatalysts for hydrogen production, also providing an efficient and sustainable method to valorize these wastes.