Use of carbon points in electrochemical processes and energy storage

February 24, 2022

(News from Nanowerk) Thanks to their unusual optical properties, carbon particles with a diameter on the order of a few nanometers – called carbon dots – hold great promise for a wide range of technological applications, as diverse as energy conversion and bio-imaging.

Additionally, carbon dots (CDs) have several practical advantages as they are easy to manufacture, stable, and do not contain toxic heavy metals. Their versatility is largely due to the fact that, depending on their chemical composition and aspects of their complex structure, they can either act as light emitters in the form of photoluminescence or function as photocatalysts by absorbing light energy and triggering chemical reactions, such as water splitting.

In addition, their superior electrochemical activity and ease of modification make carbon dots very promising electrode materials for electrocatalysis and electrical energy storage.

The structure of CDs usually consists of a nucleus composed of sp2/sp3 hybrid carbon atoms and an amorphous shell with many functional groups or polymer chains containing O/N. According to the microstructure of carbon nuclei, CDs are further divided into graphene quantum dots (GQD), carbon quantum dots (CQD), carbon nanodots (CND) and carbonized polymer dots (CPD)

Four categories of carbon dots and their structures: graphene quantum dots (GQD), carbon quantum dots (CQD), carbon nanodots (CND) and carbonized polymer dots (CPD). (Reproduced with permission from Wiley-VCH Verlag)

A review in Advanced Energy Materials (“Carbon Dots as New Building Blocks for Electrochemical Energy Storage and Electrocatalysis”), summarizes recent advances in DC-based electrode materials, including methods of synthesis, structure and physiochemical properties of DCs, and strategies for modification and functionalization, with particular emphasis on the relationships structure-property.

The article also discusses the applications of electrodes containing H-CDs2/O2 evolution, O2 reduction, CO2 reduction, capacitors and batteries.

Schematic illustration of CD synthesis via top-down and bottom-up methods. (Reproduced with permission from Elsevier)

DCs, due to their unique structural and physicochemical characteristics, are considered promising electrode candidates for supercapacitors and batteries. In their article, the authors therefore synthesize recent research in this field, highlighting the advantages of CDs in such devices. They deal with the separation of water to produce H2 and co2 reduction to fuels compared to electrodes containing CDs, which are also efficient technologies for storing electrical energy.

Although many encouraging results have been obtained so far, research on DC-based electrode materials is still in its infancy. This research focuses on five key functions of the application of carbon points in the storage and conversion of electrochemical energy through various processes:

As active centers to provide more electrochemically active sites through inherent structural defects, abundant surface/edge functional groups, and heteroatomic doping;

As regulators to adjust the electronic state and local charge distribution of active centers in other catalytic materials, thereby altering the adsorption capacity of the catalyst to reaction intermediates;

As structural stabilizers to anchor and disperse active components through abundant surface functional groups, to reduce agglomeration of active materials by forming a restricted network, and to attenuate volume changes during the charge-discharge process by forming protective/buffer layers;

As structural agents to induce the crystallization and growth of metallic nanomaterials to form electrochemically beneficial morphologies and microstructures;

As conductive agents to boost ion diffusion and charge transfer kinetics.

As this review illustrates, DC-based materials have unique advantages and great potential in electrochemical energy conversion and storage systems. The authors conclude that with the discovery of advanced methods of synthesis and characterization and a deep understanding of the relationships between structure and performance of DCs, the rational design and construction of high-performance DC-based electrodes will be achieved in a near future, paving the way for the commercialization of a multitude of energy storage and conversion devices containing CD electrodes.