Doping carbons beyond nitrogen: an overview of advanced heteroatom doped carbons with boron, sulphur and phosphorus for energy applications

Abstract

Heteroatom doped carbon materials represent one of the most prominent families of materials that are used in energy related applications, such as fuel cells, batteries, hydrogen storage or supercapacitors. While doping carbons with nitrogen atoms has experienced great progress throughout the past decades and yielded promising material concepts, also other doping candidates have gained the researchers' interest in the last few years. Boron is already relatively widely studied, and as its electronic situation is contrary to the one of nitrogen, codoping carbons with both heteroatoms can probably create synergistic effects. Sulphur and phosphorus have just recently entered the world of carbon synthesis, but already the first studies published prove their potential, especially as electrocatalysts in the cathodic compartment of fuel cells. Due to their size and their electronegativity being lower than those of carbon, structural distortions and changes of the charge densities are induced in the carbon materials. This article is to give a state of the art update on the most recent developments concerning the advanced heteroatom doping of carbon that goes beyond nitrogen. Doped carbon materials and their applications in energy devices are discussed with respect to their boron-, sulphur-and phosphorus-doping. Broader contextThe research and design of novel materials that are applicable in various energy devices represent one of the central and most thriving subjects within today's scientic work. The challenges do not only rely on the tremendous need to overcome traditional fossil fuel based energy recovery. While a lot of sustainable concepts already exist, these require the development of high performance materials that are able to cope with certain challenges, e.g. the dependence on highly expensive and rather not abundantly available noble metals, and also a lack of long term stability of those. Researchers have been carrying out numerous studies concentrating on nding alternative materials that can be applied in novel energy devices. Those alternative materials should most preferably be free of noble metals, avoid expensive precursor systems, be sustainable and not rely on the fossil energy sources that are to be replaced, and of course exhibit high activity in the devices they are designed for. One class of materials in whose development and understanding researchers have put strong effort is heteroatom-doped carbon materials. By heteroatom doping the properties are altered compared to crude carbon materials. The by far most intensely studied doping candidate is nitrogen, capable of not only increasing electric conductivity, but also the catalytic activity of carbons. Such N-doped carbons have advanced tremendously in the past few years, especially by proving their usefulness as electrocatalysts for the reduction of oxygen in fuel cell cathodes, or as electrode materials in supercapacitors. Meanwhile the spectrum of doping has been widened, and novel doped carbons have been reported, indicating the promising pote...

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