A Multiphysics Finite‐Element Framework for Magnetically Tunable Electrochemical Hydrogen Sensors Based on <scp>Cs</scp> / <scp>GO</scp> / <scp> Fe ₃ O ₄ </scp> / <scp>PANi</scp> Hydrogels

ABSTRACT Hydrogen sensing is a critical requirement for the safe deployment of hydrogen‐based energy systems, necessitating sensors with high sensitivity, fast response, and tunable performance. In this study, a comprehensive multiphysics finite‐element framework is developed to investigate electrochemical hydrogen sensing using a quaternary chitosan/graphene oxide/iron oxide/polyaniline (Cs/GO/Fe 3 O 4 /PANi) hydrogel nanocomposite operating in an alkaline medium. The model integrates mass transport, electrochemical reaction kinetics, charge transport in porous media, and magnetic field effects within a unified computational platform to elucidate the coupled physicochemical mechanisms governing sensor behavior. Simulation results reveal that superparamagnetic Fe 3 O 4 nanoparticles significantly enhance effective electrical conductivity through electron‐hopping pathways and increase the density of electrochemically active sites for hydrogen oxidation. A non‐monotonic dependence of sensor performance on Fe 3 O 4 volume fraction is identified, with an optimal loading at φ Fe ≈ 0.10 yielding a maximum current density of ∼16.8 μA cm −2 , a sensitivity of ∼16.7 μA M −1 , and a rapid response time of ∼0.3 s, while higher loadings induce transport blocking and network disruption that degrade performance. Furthermore, the application of an external magnetic field enables active tunability of the sensing response, where moderate fields (B ext ≈ 0.6 T) promote partial alignment of Fe 3 O 4 nanoparticles, generating anisotropic conductive pathways that enhance reaction kinetics, reduce overpotential, and improve sensitivity by ∼22% with a shortened response time of ∼0.25 s. Damköhler number analysis further reveals transitions between kinetics‐limited, mixed‐control, and diffusion‐limited regimes, providing quantitative insight into the interplay between transport and electrochemical processes. Overall, this multiphysics finite‐element framework offers predictive design guidelines for magnetically tunable, high‐performance hydrogel‐based hydrogen sensors and supports the rational engineering of adaptive sensing platforms for hydrogen safety and energy‐related applications.

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