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 IrO 2 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.