Intercalation makes the difference with TiS2: Boosting electrocatalytic water oxidation activity through Co intercalation

Intercalated and unmodified TiS2 nanomaterials were synthesized and characterized by UV-Visible-NIR spectroscopy, Powder X-Ray Diffraction, and X-Ray Photoelectron and Ultraviolet Photoelectron Spectroscopy. Photoelectron spectroscopy measurements indicated that CoS and Cu2S appeared to be intercalated between sheets of partially or fully oxidized TiS2, which could be solution processed on conductive oxide substrates. The materials were then applied toward water oxidation and evaluated by cyclic voltammetry, chronoamperometry, and impedance measurements. While unmodified TiS2 was not observed to perform well as an electrocatalyst with overpotentials >3 V in 1 M NaOH electrolyte, CoS intercalation was found to lower the overpotential by ∼1.8-1.44 V at 10 mA/cm2. Conversely, Cu2S intercalation resulted in only a modest increase in performance (>2.3 V overpotential). Impedance measurements indicated that intercalation increased the series resistance in the as-prepared samples but decreased the series resistance in oxidized samples.