Exfoliating bulk transition metal dichalcogenides (TMDCs) into few-layered 2D nanosheets enhances Hydrogen Evolution Reaction (HER) performance, yet obtaining high-concentration aqueous dispersions without degrading material integrity remains a significant challenge. In liquid-phase exfoliation, organic solvents such as N -methyl-2-pyrrolidone (NMP) can yield high nanosheet concentrations, but their inherent toxicity restricts their suitability for practical, large-scale applications. In contrast, environmentally benign aqueous exfoliations usually limit dispersion concentrations below 0.5 mg mL –1, leading to dilute inks that require large-volume processing and multiple coating steps. Highly concentrated inks are desirable for device fabrication because they reduce the total deposition volume, minimize residual insulating surfactants, and promote uniform film formation compatible with scalable deposition techniques. Drying and redispersion cause irreversible restacking, surfactant accumulation, and reduced active sites, while centrifugation is energy-intensive and wasteful, and membrane filtration suffers from severe fouling, limiting scalable processing. This study presents a pH-responsive “capture-and-release” strategy using zwitterionic magnetic nanoparticles whose surface charge reversibly switches from positive at pH 3 to negative at pH 8, enabling cyclic electrostatic capture and release of TMDC nanosheets. A 10-fold concentration increase, from 0.4 to 4 mg mL –1, is achieved for few-layered MoS 2, and the approach is extended to MoSe 2 and WS 2 . Up-concentrated TMDC inks are evaluated as HER electrocatalysts, with exfoliated few-layered MoSe 2 exhibiting an overpotential of 213 mV at 10 mA cm –2 and a Tafel slope of 68 mV dec –1, values comparable to reported unmodified TMDC nanosheet-based HER catalysts. The method offers a general route to enrich surfactant-stabilized dilute 2D dispersions of few-layered TMDC nanosheets for single-component or composite HER catalytic inks.
Sohel Reja (Sat,) studied this question.