Electrochemical transformation of 2D materials to their quantum dots

The term two-dimensional (2D) material refers to a single layer of monatomic units or molecules that reveals distinct electrical and optical properties and has received much attention recently due to its immense application potential. For example, graphene as a monolayer has captured intense efforts during the past decade, and other 2D materials like transition metal dichalcogenides, phosphorene, borophene, bismuthene, and stanene have also evolved for various applications such as nanoelectronics, hydrogen storage, supercapacitors, and solar cells. More recently, their heterostructures including Janus layers have also emerged with several exceptional electronic properties. Although there are several ways of synthesizing quantum dots of these exciting materials, electrochemical methods are especially relevant for preparing 2D materials (often in a size-controlled manner) from suitable precursors. More importantly, hetero-atom doping could also be carried out at room temperature when these materials are prepared by applying electric field without any major change in the morphology or size distribution after doping. With this disposition, we summarize the essential experimental methodology and a few mechanistic insights for the electrochemical synthesis of quantum dots from different 2D materials. This topic has not been discussed unambiguously in the past, lacking the proper motivation to emphasize the importance of controlling the electric field, substrate electrodes, precursors, and the role of counter ions during the synthesis. In this review, we concisely discuss the synthesis of such 0D materials by electrochemical methods, the mechanism, advantages, and limitations in comparison with other methods, along with the benefits ensued for a few selected applications. The genre of this category of work has always been intriguing despite the fact that only a few other groups are involved in the synthetic methodology, making the topic an everchanging field of exciting applications ranging from flexible power sources for wearable electronics to green electrocatalysts for sustainability and nano-sensors for biological applications.