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

Abstract 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 MoO₂ 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 H₂O 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.