Amorphous Yolk–Shelled ZIF-67@Co3(PO4)2 as Nonprecious Bifunctional Catalysts for Boosting Overall Water Splitting

It is challenging to generate inexpensive and noble metal-free catalysts for efficient overall water splitting (OWS). To achieve this goal, suitable tuning of the structure and composition of electrocatalytic materials is a promising approach that has attracted much attention in recent years. Herein, novel hybrid amorphous ZIF-67@Co3(PO4)2 electrocatalysts with yolk–shell structures were prepared using a reflux method. It is demonstrated that yolk–shelled ZIF-67@Co3(PO4)2 is not only an active catalyst for the hydrogen evolution reaction (HER) but also an efficient catalyst for the oxygen evolution reaction (OER). The optimized composite electrode showed superior performance with low overpotentials of 73 and 334 mV @ 10 mA·cm–2 toward HER and OER, respectively, and a low potential of 1.62 V @ 10 mA·cm–2 and 1.66 V @ 30 mA·cm–2 in a practical OWS test under alkaline conditions. N–O bonds were formed to connect the two components of ZIF-67 and Co3(PO4)2 in the composite ZIF-67@Co3(PO4)2, which indicates that the two components are synergistic but not isolated, and this synergistic effect may be one of the important reasons to boost the oxygen and hydrogen evolution performances of the hybrid. Based on experimental data, the high electrocatalytic performance was inferred to be related to the unique structure of ZIF-67, tuning the ability of Co3(PO4)2 and synergism between ZIF-67 and Co3(PO4)2. The preparation strategy reported herein can be extended for the rational design and synthesis of cheap, active, and long-lasting bifunctional electrocatalysts for OWS and other renewable energy devices.