Confinement in two-dimensional materials: Major advances and challenges in the emerging renewable energy conversion and other applications

Energy production highest demand with low-carbon emission is very critical and can be achieved by introducing new low cost but more stable and active electrocatalyst that can improve the efficiency of existing or newly proposed renewable energy devices. Nowadays, oxygen/hydrogen evolution reactions (OER/HER) in water (H₂O) electrolysis is important to cost-efficient formation of pure hydrogen (H₂) fuel, while oxygen reduction reaction (ORR) in fuel cells are experiencing a sluggish reaction kinetics still when load more quantity of precious metals, like benchmark Pt. Therefore, this study is motivated by a requirement to substitute rare precious metal catalysts by nonprecious metals catalysts (NPMCs) two-dimensional materials (2DMs). The 2DMs have a broad significance due to their nano- and atomic-level applications and some of them with prominent electrical properties, which plays very important role in electrocatalytic applications. The NPMCs 2DMs are more efficient than the conventional precious metals based electrocatalysts, as they present flexible electrode configuration, excellent catalytic activity, and high stability, especially in their composite form. In this review we will explain in detail about the 2D based electrocatalysts; those demonstrate high efficiency, selectivity and sustainability for ORR, OER, and HER. The most important point related to electrocatalytic applications of the 2DMs efficiency enhancement is newly introduced confinement effect, and we will mainly concentrate on 2DMs based confinement effect. The diverse ways for modifying electronic states of the 2D confinement electrocatalysts are emphasized and prospects on confinement catalysis by using 2DMs to energy conversion are given. The perspectives on the relevant areas about further enhancement in their properties will also propos and address. Finally, we will discuss in detail about recent progresses made till now and future predictions about the 2DMs in energy producing devices.