Plasma-Chemical Integration of Solution-Derived ATTT with 3D Carbon Nanowalls for Controllable WS₂/WO _x Hybrid...

Two-dimensional (2D) tungsten disulfide (WS₂) has attracted considerable interest as a pseudocapacitive material, yet its practical application is often hindered by limited electrical conductivity, complex fabrication routes, and the need for binders. Here, we report a plasma-chemical route for fabricating binder-free, composition-tuned WS₂/WO _x @CNW hybrid electrodes from solution-deposited ammonium tetrathiotungstate (ATTT) with a downstream hydrogen remote plasma process. By systematically varying the ATTT concentration and microwave power, the surface chemistry of the CNW scaffold is controllably routed into CNW-dominant, WS₂-rich, S-oxide-rich, and WO _x -dominant regimes while preserving the overall three-dimensional CNW framework, despite partial surface masking at high oxide coverage. Structural and chemical analyses reveal that incomplete plasma conversion at high ATTT and low power leaves sulfur-rich species that are prone to oxidation, whereas high power promotes sulfur-vacancy formation and W-rich surfaces that preferentially evolve into WO _x upon air exposure. Electrochemical measurements demonstrate that introducing WS₂/WO _x functionalities markedly enhances areal capacitance relative to bare CNWs. The WO _x -dominant electrode delivered the highest areal capacitance among the tested electrodes, 91.1 mF cm^-2 at 0.1 V s^-1 and 21.7 mF cm^-2 at 1.0 V s^-1, compared with 4.6 and 3.15 mF cm^-2 for bare CNW, respectively, although this gain was accompanied by increased interfacial and transport resistance. Dunn and impedance analyses reveal that this improvement arises primarily from increased diffusion-controlled pseudocapacitive charge storage, accompanied by a trade-off in the form of higher interfacial and transport resistance. This work elucidates how precursor loading and hydrogen-radical flux govern competitive sulfur- versus tungsten-centered oxidation pathways and provides a practical plasma-chemical framework for engineering high-performance, binder-free WS₂/WO _x @CNW hybrid electrodes for supercapacitor applications.