Biowaste-Derived Catalysts for Sustainable Electrochemical Water Splitting: A Pathway to Circular Bioeconomy

The accelerating global pursuit of carbon neutrality has intensified the need for sustainable, low-cost hydrogen-production technologies. Electrochemical water splitting, driven by renewable electricity, offers a clean pathway for hydrogen generation; however, large-scale deployment is hindered by the high cost, scarcity, and limited durability of noble-metal catalysts. In response, biowaste-derived materials have emerged as a sustainable solution, transforming agricultural, food, and marine residues into high-value electrode architectures. Naturally enriched with carbon frameworks and heteroatoms (N, S, P, B), such wastes can be converted through pyrolysis, activation, or templated synthesis into heteroatom-doped porous carbons and biocarbon-supported transition-metal hybrids with abundant defects and accelerated charge transport. These tailored electrodes deliver competitive activity for both the hydrogen evolution reaction and oxygen evolution reaction, approaching Pt and IrO₂ benchmarks while offering sustainability and scalability. This review consolidates conversion strategies, structural design principles, and catalytic mechanisms, emphasizing heteroatom modulation, metal-carbon interface engineering, and hierarchical morphology. It further establishes a structure-property-performance framework linking precursor chemistry, conversion route, and electrode architecture to catalytic behavior, while addressing fabrication strategies, benchmarking protocols, degradation mechanisms, and techno-economic relevance. By integrating waste valorization with green electrocatalysis, biowaste-derived electrodes offer a promising pathway toward circular, low-carbon hydrogen-energy systems.