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Transition metal phosphates have proved to be promising electrocatalysts for hydrogen evolution reactions (HER) of water splitting, however, further increasing their active sites and catalytic activity remains a major challenge. Herein, accordion-like Co-MOF with layered structure was synthesized. After subsequent carbonization and phosphidization, lamellar heterostructured Co/CoP nanocrystals encapsulated in a P, N co-doped C matrix (Co/CoP@PNC) was obtained. Heterojunction provides abundant active sites and improves electron transfer rate. Additionally, the effect of phosphating degree on the electrocatalytic activity was studied. In the alkaline electrolyte, the current density of the optimized Co/CoP@PNC-10 for HER reached 10 mA cm−2 at overpotential of 137 mV in 1.0 M KOH, which was superior to most of transition metal-based electrocatalysts. This work provides new guidance for the design and development of transition metal-based electrocatalysts. Co/CoP heterojunction embedded in P, N co-doped C matrix (Co/CoP@PNC) was prepared through further carbonization and phosphidization, the optimized Co/CoP@PNC exhibited excellent catalytic activity for alkaline HER. [Display omitted] • With accordion-like Co-MOF as the precursor, Co/CoP heterojunction embedded in P, N co-doped C matrix (Co/CoP@PNC) was prepared through further carbonization and phosphidization. • The phase and catalytic activity of the sample are related to the phosphating degree. • The optimized Co/CoP@PNC-10 exhibited the best performance among the series, with an overpotential of 137 mV at a current density of 10 mA cm−2 for alkaline HER. • P, N co-doped C substrate and Co/CoP heterojunction promote the overall HER performance through synergistic effect. [ABSTRACT FROM AUTHOR]

• This review provides an introduction to the characteristics and advantages of MOF electrocatalysts, as well as an overview of the primary mechanism involved in water electrolysis. • The application of MOF-based electrocatalysts in water splitting is reviewed. • The preparation, modification, and catalytic activity of electrocatalysts for MOF derivatives are summarized. Green hydrogen is generated by water electrolysis using renewable energy sources. For green hydrogen to become cost-effective in front of hydrogen production from fossil fuels, highly active, efficient, and durable electrocatalysts based on abundant and low-cost elements need to be developed. Great efforts have been invested in designing and engineering water-splitting electrocatalysts with optimized compositions and architecture. In this last direction, metal–organic framework (MOF) compounds have received particular attention on account of their high specific surface area (SSA) and excellent chemical stability. This work affords an overview of the latest progress in the design, engineering, and application of MOFs and their derivatives as electrocatalysts in water splitting. It further discusses the challenges encountered and the new research directions and application prospects. First, the characteristics and advantages of MOF electrocatalysts and the main mechanism of water electrolysis are introduced. Next, the research progress on the application of MOFs and their derivatives in water electrolysis is reviewed, with special emphasis on the preparation, modification, and catalytic activity of the catalysts. Finally, the present challenges and future development prospects of MOFs as water-splitting electrocatalysts are discussed. Overall, this review aims to provide new insights into the design and synthesis principles of MOF materials, promoting their practical application in water splitting, and further broadening their future uses. [ABSTRACT FROM AUTHOR]