The Critical Role of Oxygen-Containing Functional Groups in the Etching Behavior of Activators to Carbon Materials

Abstract

Fully activating the carbon matrix to obtain a high specific surface area (SSA) has been a practical approach to enhance the electrochemical performance of carbon materials. Much research mentioned that the activation has a large influence on the oxygen-containing functional groups (OCFGs) of the porous carbon. However, the potential impact of OCFGs ubiquitous in carbon precursors on the etching behavior of activators is rarely studied. Herein, a pitaya peel with a high oxygen content is employed as the carbon matrix and then a series of porous carbon materials are synthesized by a one-step pyrolysis strategy using different activators. We found that the existence of OCFGs in the carbon materials is conducive to enhancing the etching behavior. Theoretical calculations reveal that OCFGs in the carbon matrix could induce the local charge redistributions, thereby improving the binding affinity between the activators and the carbon atoms near OCFGs. Consequently, activators tend to etch carbon atoms around the OCFGs in the carbon precursors. Based on this, the optimized sample exhibits an ultrahigh SSA of 3699 m 2 g −1 , superior capacitance (373 F g −1 at 1 A g −1 ), and excellent rate performance. This work contributes to understanding the role of OCFGs in the etching behavior of activators to carbon materials.

Synthesis, characterisation and carbon dioxide capture capacities of hierarchically porous Starbons®

“…X300's were selected as substrates for potassium hydroxide activation as they retain oxygen-containing functional groups which facilitate potassium hydroxide activation. 35 Carbon dioxide and oxygen activated materials were prepared from X800's since Starbons ® which have been carbonised at 800 °C retain far fewer oxygen containing functional groups than Starbons ® prepared at 300 °C. Hence, use of X800's as the activation precursor allowed the activation to be better controlled and monitored by TGA-IR.…”

ZnCl2 as a “Nitrogen Bank” to Inhibit Nitrogen Loss during the Thermal Conversion of Nitrogen-Containing Carbon Precursors to Nitrogen-Doped Carbon

“…Moreover, the H 3 PO 4 poisoning experiment (see details in Figure S12) demonstrates that the better catalytic activity of N/C ZnCl 2 (than N/C) primarily arises from its higher N-content, especially the Py-N content (rather than carbon defects). These results suggest that the added ZnCl 2 more likely acts as a N-bank to elevate the N-content (especially the Py-N content) rather than as an activating agent (creating pores and carbon defects) in the resultant carbon materials for lowering the ORR overpotential. ,, …”

“…On the other hand, too much ZnCl 2 additive (i.e., the mass ratio of Zn-HMT:ZnCl 2 = 1:3) not only causes waste of ZnCl 2 but also leads to a significant amount of ZnO intermediate during the pyrolysis (Figure S6), which would react with the N/C and thus reduce the N-content of the synthesized carbon product. 18 These results suggest that the ZnCl 2 additive needs to be at an appropriate level to fully function as the N-bank during the synthesis.…”

“…The insufficient ZnCl 2 additive (i.e., the mass ratio of Zn-HMT:ZnCl 2 = 1:1) could not fully guarantee the N-bank effect because the NH 3 released from the Zn-HMT precursor might not be effectively captured by the ZnCl 2 at such a low quantity. On the other hand, too much ZnCl 2 additive (i.e., the mass ratio of Zn-HMT:ZnCl 2 = 1:3) not only causes waste of ZnCl 2 but also leads to a significant amount of ZnO intermediate during the pyrolysis (Figure S6), which would react with the N/C and thus reduce the N-content of the synthesized carbon product . These results suggest that the ZnCl 2 additive needs to be at an appropriate level to fully function as the N-bank during the synthesis.…”

“…These results suggest that the added ZnCl 2 more likely acts as a N-bank to elevate the N-content (especially the Py-N content) rather than as an activating agent (creating pores and carbon defects) in the resultant carbon materials for lowering the ORR overpotential. 18,24,25 The average electron transfer number (n) of the ORR on N/ C ZnCl 2 was obtained by using the K−L equation (see details in SI). The n is calculated to be around 4.0 (Figure 3b), implying that the N/C ZnCl 2 , like the Pt/C, catalyzes the ORR in a direct 4e − pathway.…”