Hydrogel Electrocatalysts: Engineering the Electrochemical Double Layer (EDL) for Advanced Electrocatalysis

Hydrogel electrocatalysts have garnered significant attention due to their unique three-dimensional porous architectures and readily tunable physicochemical properties. These intrinsic characteristics synergistically enhance mass transport, accessibility of active sites, and reaction kinetics in electrocatalytic processes. The electrochemical double layer (EDL), a nanoscale charge-separation structure at the electrode-electrolyte interface, fundamentally governs electrocatalytic activity. Critically, the hierarchical architecture and chemical functionality of hydrogels allow targeted modulation of EDL microenvironments, thereby elevating catalytic performance. This review provides the first comprehensive analysis integrating fundamental EDL principles with hydrogel electrocatalyst design. It first delineates the evolution of EDL theoretical frameworks, from the Helmholtz model to the Gouy-Chapman-Stern model and the modern Bockris-Devanathan-Müller model. Subsequently, it examines hydrogel-specific EDL behaviors such as hierarchical pore effects, hydration dynamics, ion enrichment, and functional group modifications. Key optimization strategies are systematically categorized and evaluated. These include hierarchical porosity design, active site engineering, interfacial hydration control, and synthesis of hydrogel-derived carbons. Finally, the review outlines emerging challenges and future prospects in the development of advanced hydrogel electrocatalysts. This work enhances the theoretical understanding of interfacial processes in hydrogels and supports the rational design of high-performance hydrogel electrocatalysts.