Positively Charged Hollow Co Nanoshells by Kirkendall Effect Stabilized by Electron Sink for Alkaline Water Dissociation.

While cobalt (Co) exhibits a comparable energy barrier for H * adsorption/desorption to platinum in theory, it is generally not suitable for alkaline hydrogen evolution reaction (HER) because of unfavorable water dissociation. Here, the Kirkendall effect is adopted to fabricate positive-charged hollow metal Co (PHCo) nanoshells that are stabilized by MoO 2 and chainmail carbon as the electron sink. Compared to the zero-valent Co, the PHCo accelerates the water dissociation and changes the rate-determining step from Volmer to Heyrovsky process. Alkaline HER occurs with a low overpotential of 59.0 mV at 10 mA cm -2 . Operando Raman and first principles calculations reveal that the interfacial water to the PHCo sites and the accelerated proton transfer are conducive to the adsorption and dissociation of H 2 O molecules. Meanwhile, the upshifted d-band center of PHCo optimizes the adsorption/desorption of H * . This work provides a unique synthesis of hollow Co nanoshells via the Kirkendall effect and insights to water dissociation on catalyst surfaces with tailored charge states.