Biochar-Based Catalysts in Hydrogen Production: Mechanisms, Activation, and Efficiency

Biochar, a carbon-rich material derived from biomass, has emerged as a promising catalytic platform owing to its low cost, wide availability, structural tunability, and environmental compatibility. This review provides a critical and mechanistically integrated assessment of biochar-based catalysts for sustainable hydrogen production across thermochemical and photochemical pathways. Rather than cataloging reported yields, the analysis adopts a standardized normalization framework, expressing hydrogen productivity primarily as mmol H₂ g⁻¹ catalyst h⁻¹ to enable reliable cross-study comparison. The review introduces a unified structure–property–performance perspective linking feedstock chemistry, activation strategy, and metal–carbon interactions to pathway-specific hydrogen productivity. Evidence indicates that feedstock-derived chemistry often exerts a stronger influence on catalytic behavior than pyrolysis temperature alone, while controlled metal doping—particularly with Ni, Fe, and Co—enhances active-site accessibility and stability. Activation treatments modulate porosity and surface functionality, yet excessive modification may induce structural degradation or catalyst deactivation. Beyond catalytic efficiency, biochar-based systems offer sustainability advantages through biomass valorization, reduced reliance on critical raw materials, and compatibility with circular carbon strategies. By integrating mechanistic insight, normalization rigor, and sustainability considerations, this review positions biochar not merely as a low-cost alternative support, but as a tunable catalytic platform for next-generation hydrogen technologies. HIGHLIGHTS Biochar provides a tunable catalytic platform for sustainable hydrogen production from biomass resources. Metal–carbon interactions significantly enhance catalytic activity, stability, and coke resistance. tructural tuning of biochar optimizes porosity, surface functionality, and thermal durability. Normalized hydrogen productivity enables consistent comparison across heterogeneous studies. A unified mechanistic framework guides rational design of next-generation biochar catalysts. GRAPHICAL ABSTRACT