Biochar-derived carbon nanomaterials for sustainable hydrogen production: Synthesis, electrocatalytic performance, and future perspective

Hydrogen is a clean energy carrier with zero carbon emissions at the point of use. Carbon-neutral hydrogen production through water electrolysis is promising approach for sustainable energy generation; however, its efficiency largely depends on development of efficient and stable electrocatalysts. Carbon nanomaterials, including carbon nanotubes (CNTs), graphene, and carbon quantum dots, nanosheets, and nanoflakes, offer high surface area, tunable structures, excellent electrical conductivity, and favourable electrocatalytic properties, making them promising materials for enhancing hydrogen evolution reaction(HER) performance. Biochar has emerged as a sustainable and low-cost precursor for synthesis of carbon nanomaterials because its carbon-rich structure can be transformed and modified through processes such as sonication, hydrothermal treatment, ball milling, and other nanoscale structural modification. These approaches enable the production of diverse carbon nanostructures, tailored physicochemical and electrochemical properties. This review critically examines recent advances in biochar-derived carbon nanomaterials as sustainable hydrogen production, with particular emphasis on their synthesis, structural characteristics, electrocatalytic properties, and applications in electrochemical hydrogen generation. The relationship between nanomaterial structure, surface characteristics, catalytic activity, and energy conversion efficiency is discussed to provide a comprehensive understanding of their role in hydrogen evolution. The review further highlights the potential of biochar-derived nanomaterials as sustainable platforms for developing efficient, low-cost, and scalable electrocatalysts that can contribute to the advancement of green hydrogen production and carbon-neutral energy systems.