Review carbon onions for electrochemical energy storage

Are carbon onions electrode materials?

This review provides a critical discussion of the electrochemical properties of different types of carbon onions as electrode materials. It also compares the general advantages and disadvantages of different carbon onion synthesis methods.

What are the physical and chemical properties of carbon onions?

The physical and chemical properties of carbon onions, in particular nanodiamond-derived carbon onions, are described with emphasis on those parameters especially important for electrochemical energy storage systems, including the structure, conductivity, and porosity.

Why do onions improve electrochemical performance?

They attributed this improvement in the electrochemical performance of the onion like endohedral (Ni, Fe) carbon due to the graphitic nature and the pseudocapacitance mechanism occurring between the surface groups like oxygen and nitrogen through the faradaic reaction on the surface of the electrode respectively [ 290 ].

What are carbon onions used for?

The vast majority of electrochemical applications of carbon onions relates to their use for supercapacitor electrodes as an active material, conductive additive, or substrate for redox-hybrid systems. In contrast, only a few studies have investigated their use as anode materials for battery systems, such as lithium ion batteries.

Are carbon onions a supercapacitor electrode?

Carbon onions as supercapacitor electrode materials present a superior rate handling behavior but suffer from a comparatively low specific energy. To overcome this issue, composites with metal oxides, conducting polymers, other redox species, as well as creation of surface functional groups can be used to induce the redox activity of carbon onions.

What influences the electrical conductivity of carbon onion electrodes?

The electrical conductivity of carbon onion electrodes is influenced by the intrinsic electrical conductivity of the material, the degree of particle sintering, the particle arrangement and compaction, as well as the electrode preparation (e.g., use of binder vs. binder-free electrodes).