Recent advances in functionalizing ZIFs and their derived carbon materials towards electrocatalytic water splitting

Hydrogen energy, as a promising alternative to accomplish the energy conversion and storage, has inspired tremendous research interests in the past decades. Particularly, the green hydrogen production by electrocatalytic water splitting (EWS) is crucial for the advance of renewable and clean energy resources. However, the sluggish anodic oxygen evolution reactions (OER) and cathodic hydrogen evolution reactions (HER) are prime roadblocks for the commercial application. The exploration of efficient, durable and low-cost bifunctional electrocatalysts for OER and HER is pivotal for the scalable production of green hydrogen through EWS. Zeolitic imidazolate frameworks (ZIFs), consisted of metal cations and organic ligands, are emerging as prominent precursors for the exploration of bifunctional electrocatalysts for water splitting owing to their unique characteristics, such as 3D porous networks, large specific surface area, tunable composition, variable architecture, as well as high chemical and thermal stability. By pyrolysis of ZIFs, the resultant carbon materials have nearly inherited the merits of ZIFs and are also famous for various actives species, i.e., self-doped nitrogen, metal- nitrogen, and metal nanoparticles/alloy/metal oxides, etc., which are beneficial to the electrocatalytic performance. In this review, we survey the recent progress in developing of efficient OER and HER bifunctional electrocatalysts for EWS, highlighting different modification strategies for the preparation of ZIFs-derived multi- doped porous carbon materials. First, the general descriptions of EWS and ZIFs materials are introduced. Subsequently, the pristine ZIFs derived carbon materials and their catalytic performance are presented. Afterwards, the pre-modification, in-situ modification and the post-modification of ZIFs and the resulting carbon materials are detailed in Section 3, 4 and 5, including the synthetic methods, electrocatalytic performance, the correlations of composition-structure-performance. Finally, we summarize the corresponding challenges and future perspectives in this rapidly growing field.