Glucose-derived hydrothermal carbons as energy storage booster for vanadium redox flow batteries

Fabricating of high performance electrodes by a sustainable and cost effective method is essential to the development of vanadium redox flow batteries(VRFBs).In this work,an effective strategy is proposed to deposit carbon nanoparticles on graphite felts by hydrothermal carbonization method.This in-situ method minimizes the drop off and aggregation of carbon nanoparticles during electrochemical testing.Such integration of felts and hydrothermal carbons(HTC)produces a new electrode that combines the outstanding electrical conductivity of felts with the effective redox active sites provided by the HTC coating layer.The presence of the amorphous carbon layers on the felts is found to be able to promote the mass/charge transfer,and create oxygenated/nitrogenated active sites and hence enhances wettability.Consequently,the most optimized electrode based on a rational approach delivers an impressive electrochemical performance toward VRFBs in wide range of current densities from 200 to 500 mAcm^-2.The voltage efficiency(VE)of GFs-HTC is much higher than the VEs of the pristine GFs,especially at high current densities.It exhibits a 4.18 times increase in discharge capacity over the pristine graphite felt respectively,at a high current density of 400 mAcm^-2.The enhanced performance is attributed to the abundant active sites from amorphous hydrothermal carbon,which facilitates the fast electrochemical kinetics of vanadium redox reactions.This work evidences that the glucose-derived hydrothermal carbons as energy storage booster hold great promise in practical VRFBs application.

Improving ORR activity of carbon nanotubes by hydrothermal carbon deposition method

Nitrogen doped carbons are an important family of materials with ideal activity for oxygen reduction reaction(ORR). It is always interesting to search functional carbons with high heteroatom contents and desirable structure for ORR. Within this study, the surface modification of carbon nanotubes(CNTs) via hydrothermal carbonization(HTC) technique in the presence of glucose and urea was reported, where the surface of CNTs is successfully coated by nitrogen containing hydrothermal carbon layers. The resulting composite combines both advantages of the outstanding electrical conductivity of CNTs and the effective ORR active sites provided by doped nitrogen in the HTC carbon layers. By controlling the ratio of glucose and urea, the nitrogen contents coated on the surface of CNTs can reach up to 1.7 wt%. The resulting materials show outstanding electrochemical activity towards ORR in alkaline electrolyte, making it one of the valuable metal-free electrode materials and a competent alternative to the state-of-the-art Pt/C catalyst.

Two dimensional nanocarbons from biomass and biological molecules:Synthetic strategies and energy related applications

Two-dimensional(2D)carbon materials with ultrathin thickness,large lateral size,large surface area,accessible active sites and unique physical-chemical properties have been proven to be attractive electrode materials or catalysts for high-efficient energy storage and conversion materials.However,the conventional synthesis method for 2D carbon materials heavily depends on fossil-based feedstocks and goes through harsh conditions(e.g.,chemical vapor deposition),which are unsustainable and costly.Besides,the top-down method needs to use massive strong acids/oxidants,which is environmentallyunfriendly.Therefore,it is necessary to commit to seek green,sustainable and cost-effective approach for the synthesis of 2D carbon materials.As of now,biomass or biological molecules as carbon-rich resources have been viewed as a promising candidate for the 2D carbon material preparation owing to its abundance,renewability,nontoxicity and low-cost.Especially for nucleobases,as an emerging molecule have been shown great advantages for the construction of 2D materials guided by its multiple hydrogen-bonding interaction.Recently,our group have proposed a rather innovative strategy to produce 2D carbon materials by carbonization of nucleobases which has relatively high electrode potentials.These nucleobases can form planar network structure through hydrogen bonding interaction.Such hydrogenbonding can be stable at relatively high temperature,which confines C-C or C-N polymerization in a 2D plane.As a result,direct carbonization of nucleobases enables the formation of 2D carbon with highly sp2-conjugated and feature of heteroatom doping.This review systematically summarizes the recent development of the strategies to synthesize 2D sustainable carbon materials from biomass and biological molecules.The corresponding electrochemical applications such as lithium ion batteries,supercapacitors and fuel cell are selectively presented.At the end,the summary and future perspectives in this important field are provided to inspire further exploration.