Building microspheres-nanosheets structure in N-doped carbon to improve their performance in oxygen reduction reaction and vanadium redox flow battery
Presented here is a facile, sustainable and green method for the synthesis of N-doped carbon microspheres/nanosheets via hydrothermal carbonization (HTC) of the selected bioprecursor guanosine. The morphology of such carbons presents hierarchical microstructure consisted of carbon microspheres and carbon nanosheets with relatively disordered but mainly sp2 hybridized graphitic structure. Control experiments indicate that the formation of carbon microspheres was mainly related to the HTC process of ribose component in guanosine, while the carbon nanosheets likely originated from the self-templating effect of guanine component in guanosine. This kind of HTC product (Go-HTC-1000) properly compensates for the disadvantages of ribose-based counterpart (such as monotonously microporous structure and non-nitrogen doped nature) as well as guanine-based counterpart (such as low specific surface area and low HTC carbon yield), leading to the formation of a completely new carbon with in-situ high-level nitrogen dopant, moderate defective structure and developed hierarchical porous texture. Owing to such unique morphology and structural features, it is expected to be superior in several catalytic reactions. When representatively using as an electrocatalyst for oxygen reduction reaction (ORR), it exhibits superior performance with a very positive half-wave potential of 0.850 V (vs. RHE) comparable to Pt/C catalyst (0.855 V) and excellent stability. As for serving as an electrode material for vanadium redox reflow batteries (VRFBs), it shows significantly improved performances in both positive and negative reactions compared to the pristine graphite felts (GFs), performing well at various current densities ranging from 100 mA cm-2 to 500 mA cm-2, and achieving high energy efficiency and good rate performance. The work is believed to inspire a new perspective for the facile but efficient fabrication of novel carbon-based materials with high added values.