N/P Co-doped Micro-/Mesoporous Carbons Derived from Polyvinyl Pyrrolidone–Zn0.2@ZIF-67 with Tunable Metal Valence States towards Efficient Water Splitting

Abstract

The enhancement of electrocatalytic water splitting by modulating the intrinsic electronic environment of active sites has recently attracted lots of interest. Herein, cobalt-cobalt oxide (CoOx) at carbons derived from metal-organic frameworks (Zn0.2@ZIF-67) have been modulated by using post-phosphine (P-CoOx/NCs), acid leaching (Co/NCs), and oxidation (O−CoOx/NCs) treatments. With the assistance of polyvinyl pyrrolidone, the resultant carbons obtain a high surface area (645.7 m2 g−1) as well as a micro-/mesoporous system after carbonization at 920 °C. These advantages not only enhance the catalytic performance of catalysts, but also facilitate the charge transfer between interfaces towards the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). As a result, the constructed water splitting cell fabricated with 900P-CoOx/NCs requires a low overpotential (89 mV and 343 mV vs. reservable hydrogen electrode respectively) to drive HER and OER at 10 mA cm−2, a low cell voltage (1.69 V), and a high stability with only 4.9 % decay after 15 hours operation in the alkaline medium.