Yunpeng Huang

Controllable Synthesis of Ultrathin NiCo2O4 Nanosheets Incorporated onto Composite Nanotubes for Efficient Oxygen Reduction

Exploring non-precious-metal-based oxygen reduction reaction (ORR) electrocatalysts featuring high efficiency, low cost, and environmental friendliness is of great importance for the broad applications of fuel cells and metal-air batteries. In this work, ultrathin NiCo2 O4 nanosheets deposited on 1D SnO2 nanotubes (SNT) were successfully fabricated through a productive electrospinning technique followed by a sintering and low-temperature coprecipitation strategy. This hierarchically engineered architecture has ultrathin NiCo2 O4 nanosheets uniformly and fully erected on both walls of tubular SNTs, which results in improved electrochemical activity as an ORR catalyst, in terms of positive onset potential and high current density, as well as superior tolerance to crossover effects and long-term durability with respect to the commercial Pt/C catalyst. The excellent performance of SNT@NiCo2 O4 composites may originate from their rationally designed hierarchical tubular nanostructure with completely exposed active sites and interconnected 1D networks for efficient electron and electrolyte transfer; this makes these composite nanotubes promising candidates to replace platinum-based catalysts for practical fuel cell and metal-air battery applications.

Low-crystalline mesoporous CoFe2O4/C composite with oxygen vacancies for high energy density asymmetric supercapacitors

Recently, nano/micro-scale Fe-based ferrites with high electrochemical performances have attracted extensive attention. However, almost all the mixed Fe-based oxide research paid close attention to the crystalline phase, despite the low-crystalline or amorphous phase possessing excellent electrochemical performance. Herein, a low-crystalline mesoporous cobalt ferrite and carbon composite (L-CoFe2O4/C) material with high surface area and superior electrical conductivity was prepared via a simple citric acid assisted sol–gel approach and calcination process. The L-CoFe2O4/C electrode exhibits an unprecedented specific capacitance (600 F g−1 at 1 A g−1), which precedes some of the reported mixed Fe-based ferrite electrodes and their crystalline counterparts. The excellent electrochemical performance can mainly be attributed to the sufficient diffusion and reaction of electrolyte ions, more surface defects (e.g. oxygen vacancies) for redox reactions, and the predominant electro-conductivity of the composite during the charging/discharging process. Moreover, an L-CoFe2O4/C-based asymmetric supercapacitor exhibited high energy density and power density, and outperformed most of the reported mixed Fe-based symmetric and asymmetric supercapacitors. These findings promote new opportunities for low-crystalline Fe-based metal oxides as high performance energy storage devices.

Pseudocapacitive performance of binder-free nanostructured TT-Nb2O5/FTO electrode in aqueous electrolyte

TT-Nb2O5 nanoparticles grown on electrically conducting fluorine-doped tin oxide (FTO) glass were successfully synthesized by a facile one-pot hydrothermal method at low temperature. The as-prepared nanostructured TT-Nb2O5/FTO was directly used as the working electrode to investigate its pseudocapacitive performance without any binder or conductive agent, which exhibited a high specific capacitance of 322 F g-1 at a current density of 3.68 A g-1, excellent rate capability (258.1 F g-1 at a high scan rate of 100 mV s-1 is about 91.6% of that at 5 mV s-1), and good cycling stability (the capacitance retention is 74.3% after 3000 cycles). More importantly, it is the first time electrochemical measurements for Nb2O5 electrode in aqueous electrolyte, which are low-cost and easy to operate, have been carried out.

NiMoO4 nanorod deposited carbon sponges with ant-nest-like interior channels for high-performance pseudocapacitors

The mounting challenges of global energy shortage and climate change call for the development of low-cost and high performance energy storage systems. Here, we propose the facile preparation of a 3D sponge electrode material by the uniform deposition of NiMoO4 nanorods on a carbonized melamine sponge (CMS) during a solvothermal reaction. Under the templating of a macroporous CMS backbone, the obtained 3D hierarchical NiMoO4/CMS composite sponge can offer numerous electrochemical sites for faradaic redox reactions and also provide interconnected conducting carbon networks for direct and rapid charge transfer. Particularly, the unique ant-nest-like interior channels in the NiMoO4/CMS composite sponge can ensure fast ion transportation and also buffer the volume change of NiMoO4 during the long-term cycling. Benefiting from these advantages, the NiMoO4/CMS composite electrode exhibits a high specific capacitance of 1689 F g−1 at 1 A g−1, which outperforms most of the previously reported NiMoO4-based electrodes. Moreover, the asymmetric supercapacitor device fabricated utilizing the composite sponge as a binder-free positive electrode also delivers a superior cycling stability (91.9% capacity retention after 2500 cycles) and a high energy density of 48.8 W h kg−1 at a power density of 800 W kg−1. Hence, the current study provides a new protocol for the low-cost fabrication of 3D sponge-like electrodes towards practical supercapacitor applications.

The CoMo-LDH ultrathin nanosheet as a highly active and bifunctional electrocatalyst for overall water splitting

The development of inexpensive and bifunctional electrocatalysts based on earth-abundant elements for electrocatalytic water splitting, including the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), is of great significance. Herein, a new type of CoMo-LDH ultrathin nanosheet was synthesized as a bifunctional electrocatalyst with both OER and HER activity for full water splitting. Benefiting from the ultrathin structure and the tuned electronic structure by the doping of Mo6+, the catalyst exhibits superior OER performance with an overpotential of 290 mV to deliver a current density of 10 mA cm−2. When acting as a HER catalyst, the catalyst shows a low overpotential of 115 mV achieving a current density of 10 mA cm−2. Furthermore, the catalyst also shows bifunctional catalytic activity with a voltage of 1.63 V at 10 mA cm−2 and exhibits excellent stability for 30 h when used in the full water splitting cell. Thus, the novel CoMo-LDH ultrathin nanosheet provides a guideline for the future design of highly active and bifunctional materials for water splitting.

Hierarchical FeCo2S4 Nanotube Arrays Deposited on 3D Carbon Foam as Binder-free Electrodes for High-performance Asymmetric Pseudocapacitors

The ever-increasing global demand for green energy resources calls for more research attention on the development of cheap and efficient energy storage systems. Herein, we propose the rational design of a 3D carbon foam electrode deposited with perpendicularly oriented FeCo2 S4 nanotubes arrays (FeCo2 S4 /CMF) for high-performance asymmetric supercapacitors. In this work, the macroporous CMF served as conducting backbone not only to enhance the electrical conductivity of the composite, but also to promote the uniform growth of FeCo2 S4 nanotubes. Deposited hierarchical FeCo2 S4 nanotubes arrays with open hollow structures can afford numerous exposed electroactive sites for Faradaic redox reaction and provide short interior channels for fast electrolyte transmission. Due to these unique features, obtained 3D hierarchical FeCo2 S4 /CMF composite foam exhibits a high specific capacitance of 2430 F g-1 (specific capacity of 337.5 mAh g-1 ) at 1 A g-1 , and excellent capacitance retention of 91 % after 5000 cycles at a high current density of 9 A g-1 , which is superior to most of those previously reported binary metal sulfide-based electrodes. Moreover, asymmetric supercapacitor device assembled using the FeCo2 S4 /CMF as positive electrode also delivers a high energy density of 78.7 W h kg-1 at a power density of 800.3 W kg-1 . Therefore, this work provides a new strategy for the low-cost synthesis of 3D foam electrodes towards high-performance supercapacitor devices.