**1. Introduction**

Owing to the rapid development of modern society, the enormous demand for energy has become one of the most important issues affecting human life since twentieth century. How‐ ever, the excessive reliance on the combustion of nonrenewable fossil fuels, such as coal, petroleum, and natural gas, brings not only ecological and environmental problems but also harsh ongoing impacts on the global economy and society [1]. Hence, it has become one of the

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crucial challenges faced with our society to develop reliable and "green" approaches for energy conversion and storage.

Electrocatalytic energy conversion utilizing renewable power sources (e.g. solar and wind energy) is regarded as one of the most efficient and cleanest energy conversion pathways [2– 5]. Furthermore, the converted energy is easy to store and use as clean energy or chemical stock. Specifically, the involvement of the electrocatalytic hydrogen evolution reaction (HER) in the cathode and the oxygen evolution reaction (OER) in the anode can efficiently drive water splitting and finally convert the electrical energy into chemical form, that is, hydrogen energy [6–8]. When CO2 is reduced in the cathode while OER happens in the anode, which is the scheme of so‐called artificial photosynthesis, it converts the electrical energy into chemical forms stocked in CO or hydrocarbons [9–11]. Hence, in such context, it is urgently required in both academic and industrial fields to build our power‐supply systems based on electrocatal‐ ysis, amongst which developing efficient electrocatalysts for the aforementioned reactions is the most fundamental but vital task in this endeavour.

Two‐dimensional (2D) materials have been widely studied for their important physical and chemical properties over the last several decades [12]. Since the recent discovery of graphene [13], 2D materials have gained extensive attention since they exhibit novel and unique physical, chemical, mechanical, and electronic properties [3, 14–19]. In the abundant family of 2D materials, transition metal dichalcogenides (TMDs) have attracted significant interest and become the focus of fundamental research and technological applications due to their unique crystal structures, a wide range of chemical compositions, and a variety of material properties [5, 14, 20–24]. Recently, TMDs have emerged as one kind of efficient electrocatalysts for energy‐ related reactions, such as the HER and CO2 reduction reaction [15, 21, 25–29].
