Hydrogel-derived nitrogen-doped porous carbon framework with vanadium nitride decoration for supercapacitors with superior cycling performance

Transition metal nitrides(TMNs)and their composites with carbon materials hold tremendous potential for supercapacitor(SC)electrodes because of their excellent electronic conductivity and electrochemical activity.However,realizing cycling stable TMN/carbon-based supercapacitors with economically viable and environmentally-friendly approaches remains a significant challenge.Significantly,polyacrylamide(PAM)hydrogel,as a water-soluble linear polymer electrolyte,is expected to be a remarkable candidate precursor for preparing N-doped porous carbon(NPC)due to the high contents of carbon and nitrogen elements.In this study,vanadium nitride(VN)embedded in PAM hydrogel-derived NPC was fabricated successfully via an ammonia-free process.The VN/NPC delivers a high specific capacitance of 198.3 F g^(−1)at a current density of 1 A g^(−1),with a remarkable cycling stability of 107%after 16,000 cycles.The electrochemical performances of VN/NPC compared to bare VN nanoparticles are strongly improved due to the composite structure.Additionally,the VN/NPC-based solid-state symmetric device delivers an excellent energy density of 21.97µWh cm^(−2)at a power density of 0.5 mW cm^(−2),and an outstanding cycling durability of 90.9%after 18,000 cycles.This work paves the way to design metal nitride/porous carbon materials,which also opens up unique horizons for the recovery of hydrogel electrolyte.

Realization of high-purity 1T-MoS_(2)by hydrothermal synthesis through synergistic effect of nitric acid and ethanol for supercapacitors

Phase engineering of molybdenum disulfide(MoS_(2))can achieve phase transformation from the semiconducting phase(2H-MoS_(2))with poor conductivity to the metallic phase(1T-MoS_(2))with superior electrochemical properties.Therefore,it is desirable to prepare high concentration 1T-MoS_(2)by simple and facile methods.In this work,MoS_(2)with high concentration of 1T phase is successfully prepared by one-pot hydrothermal synthesis through the synergistic effect of HNO_(3)and CH_(3)CH_(2)OH,which is stable for more than half of a year.The as-synthesized MoS_(2)shows high capacitance of 392Fg^(-1)at 1A g^(-1)as used for supercapacitors electrodes,and displays excellent capacitance retention(83%after 10,000 cycles).Asymmetric supercapacitors(ASCs)devices assembled by the as-synthesized MoS_(2)and MnO_(2)on carbon cloths,exhibit high energy and power densities(0.194 m Wh cm^(-2)and 13.466 mW cm^(-2)).These results shed a light to realize 1T phase MoS_(2)through the synergistic effect in hydrothermal processing.

Metal/antiperovskite metal nitride composites Ag/AgNNi_(3)as novel efficient electrocatalysts for hydrogen evolution reaction in alkaline media

Searching for effective hydrogen evolution reaction(HER)electrocatalysts is crucial for water splitting.Transition metal nitrides(TMNs)are very attractive potential candidates since of high electrical conductivity,robust stability,element rich and high activity.Antiperovskite metal nitrides provide chemical flexibility since two different types of transition metal elements are contained,allowing partial substitution both for A-and M-sites.Herein,we report a novel antiperovskite metal nitride Ag_(x)Ni_(1-x)NNi_(3)(0≤x≤0.80)thin film used as highly effective HER electrocatalysts.Pure phase antiperovskite nitride can be successfully obtained for Ag_(x)Ni_(1-x)NNi_(3)with x less than 0.80.The Ag_(0.76)Ni_(0.24)NNi_(3) towards HER shows an overpotential of 122 mV at 10 mA cm^(-2)in alkaline media.Furthermore,considering the role of Ag for adsorbing hydroxyl groups,chemical engineering has been carried out for designing metal/antiperovskite nitride Ag/Ag_(x)Ni_(1-x)NNi_(3)composite electrocatalysts.The 0.18 Ag/Ag_(0.80)Ni_(0.20)NNi_(3)electrocatalyst shows a mere 13 and 81 mV of overpotential to reach 1 and 10 mA cm^(-2),respectively,showing high durability in alkaline media.These results will provide a novel type of HER catalysts based on antiperovskite metal nitrides and a strategic design for metal/antiperovskite metal nitride composite electrocatalysts for HER in alkaline media.