Iron‐Catalyzed Laser‐Induced Graphitization Enabling Current Collector‐Free Electrodes With Spatially Tunable Iron/Iron Oxide Phases

Iron‐catalyzed laser‐induced graphitization (IC‐LIG) represents an eco‐efficient alternative to traditional carbon electrode manufacturing. Combining a bio‐based tannic acid–iron precursor ink with CO 2 laser treatment results in sheet resistance of 23.59 ± 1.2Ω □ −1 on renewable substrates. Varying the tannic‐acid‐to‐iron ratio (TA:Fe), the rheology of the precursor ink can be tuned, enabling versatile application techniques, including spray coating, screen printing, and direct‐ink‐writing (DIW). Subsequent laser‐treatment enables the formation of functional IC‐LIG electrodes for all application methods, while even thick DIW‐printed layers (260 µm) result in complex, conductive electrode patterns. Laser post‐treatment expands design possibilities by locally tuning iron phases, such as converting γ‐iron to magnetite. The unidirectional laser‐treatment results in a layered arrangement, forming a multilayer electrode with a highly graphitized top layer serving as a current collector substitute, and an underlying composite of iron‐rich nanoparticles embedded in a porous graphitic foam, acting as a hybrid electrode. Electrochemical analysis reveals double‐layer capacitor behavior at low TA:Fe ratios, while higher ratios demonstrate increased redox activity and pseudo‐capacitive characteristics. Achieving stable capacities of 15 mF cm −2 with a 1 M NaCl electrolyte over 5000 cycles underscores the potential of IC‐LIG electrodes as a sustainable solution for advanced energy storage devices and beyond.