Xiaodong Lei

Ultrahigh Hydrogen Evolution Performance of Under-Water “Superaerophobic” MoS2 Nanostructured Electrodes

The adhesion of as-formed gas bubbles on the electrode surface usually impedes mass-transfer kinetics and subsequently decreases electrolysis efficiency. Here it is demonstrated that nanostructured MoS₂ films on conductive substrates show a faster hydrogen evolution reaction (HER), current increase, and a more-stable working state than their flat counterpart by significantly alleviating the adhesion of as-formed gas bubbles on the electrode. This study clearly reveals the importance of a nano-porous structure for HER, which should be general and beneficial for constructing other gas-evolution electrodes.

High pseudocapacitive cobalt carbonate hydroxide films derived from CoAl layered double hydroxides

A thin nanosheet of mesoporous cobalt carbonate hydroxide (MPCCH) has been fabricated from a CoAl-LDH nanosheet following removal of the Al cations by alkali etching. The basic etched electrode exhibits enhanced specific capacitance (1075 F g(-1) at 5 mA cm(-2)) and higher rate capability and cycling stability (92% maintained after 2000 cycles).

Sea urchin-like Ag–α-Fe2O3 nanocomposite microspheres: synthesis and gas sensing applications

Sea urchin-like Ag–α-Fe2O3 nanocomposite microspheres are developed for gas sensing applications. Such hierarchical nanostructures were synthesized by a two step approach including a hydrothermal reaction and a subsequent incipient wetness impregnation process. The large Brunauer–Emmett–Teller (BET) area and highly porous structure of the hierarchical architecture and the chemical and electronic sensitization effect of Ag nanoparticles endow the Ag–α-Fe2O3 nanocomposite microspheres with enhanced gas-sensing properties in comparison to pristine α-Fe2O3 sensors. The possible formation mechanism of the sea urchin-like nanostructures, and their sensing mechanism are discussed.

Hierarchical NiAl Layered Double Hydroxide/Multiwalled Carbon Nanotube/Nickel Foam Electrodes with Excellent Pseudocapacitive Properties

The performances of pseudocapacitors usually depend heavily on their hierarchical architectures and composition. Herein, we report a three-dimensional hierarchical NiAl layered double hydroxide/multiwalled carbon nanotube/nickel foam (NiAl-LDH/MWCNT/NF) electrode prepared by a facile three-step fabrication method: in situ hydrothermal growth of NiAl-LDH film on a Ni foam, followed by direct chemical vapor deposition growth of dense MWCNTs onto the NiAl-LDH film, and finally the growth of NiAl-LDH onto the surface of the MWCNTs via an in situ hydrothermal process in the presence of surfactant sodium dodecyl sulfate. The MWCNT surface was fully covered by NiAl-LDH hexagonal platelets, and this hierarchical architecture led to a much enhanced capacitance. The NiAl-LDH/MWCNT/NF electrode has an areal loading mass of 5.8 mg of LDH per cm(2) of MWCNT/NF surface. It also possesses exceptional areal capacitance (7.5 F cm(-2)), specific capacitance (1293 F g(-1)), and cycling stability (83% of its initial value was preserved after 1000 charge-discharge cycles). The NiAl-LDH/MWCNT/NF material is thus a highly promising electrode with potential applications in electrochemical energy storage.

Hierarchical Ni0.25Co0.75(OH)2 nanoarrays for a high-performance supercapacitor electrode prepared by an in situ conversion process

Ni0.25Co0.75(OH)2 hierarchical nanowire@nanoplatelet arrays were prepared by an in situ conversion from Ni0.5Co1.5(OH)2CO3 nanowire arrays in a highly concentrated basic solution at room temperature. These unique hierarchical nanoarrays showed a 7 times larger areal capacitance and better rate capability than the precursive one-dimensional nanowire arrays.

Nanoarray based “superaerophobic” surfaces for gas evolution reaction electrodes

Electrochemical gas evolution reactions are now of great importance in energy conversion processes and industries. Key to the improvement of catalytic performance lies the development of efficient catalytic electrodes. Besides the exploration of highly active catalysts, the fast removal of the gas products on the electrode surface should be realized because the adhered gas bubbles would block the following catalytic reactions and decrease the efficiency. In this paper, we introduce an ideal structure, a “superaerophobic” surface, to diminish the negative effects caused by the adhered gas bubbles. Several recent works focusing on addressing this issue are presented with the target reactions of hydrogen evolution and oxygen evolution. It is demonstrated that micro/nano-engineering of the catalyst directly on the current collector is a promising approach to minimize the negative effective induced by the gas bubble adhesion. In the last section, we also discuss the promise of this methodology for other energy related systems.

NiTi layered double hydroxide thin films for advanced pseudocapacitor electrodes

The performance of pseudocapacitors usually depends largely on careful manipulation of nano-architectures and suitable composition of the active materials. Herein, NiTi layered double hydroxide (LDH) thin films with uniform density were synthesized by a process including two hydrothermal treatment steps and the composition of the hexagonal NiTi-LDH nanosheets was tunable in a relatively wide range. The obtained NiTi-LDH films on nickel foam show a high areal capacitance of 10.37 F cm−2 at 5 mA cm−2, and good cycling stability (86% of its initial value was preserved after 1000 charge–discharge cycles), much better than β-Ni(OH)2 and basic nickel hydroxides carbonate {Ni2(OH)2CO3·4H2O} films. It is indicated that NH3·H2O in the reaction solution played some important roles including enlarging the particle size, focusing the size distribution, and regulating the stacking modes of NiTi-LDH on nickel foam. This work demonstrated the importance of homogeneous dispersion of Ti atoms in layered nanostructures used in supercapacitors.

Synthesis of hierarchical porous N-doped sandwich-type carbon composites as high-performance supercapacitor electrodes

Sandwich-type graphene based N-doped carbon materials (RGO@HTC) were prepared by the in situ carbonization of glucose molecules on the surface of graphene oxide sheets in the presence of ethylenediamine (EDA), followed by KOH activation to further enhance the porosity. The results revealed that hydrothermal carbon layers uniformly coated both sides of the graphene sheets, achieving sandwich-type composites with a hierarchical porous structure. The introduction of EDA with two amino terminals not only ensured the nitrogen doping into carbon composites, but also induced the hydrothermal carbonization of glucose to take place on the surface of GO as a binder. The influence of the reactant ratio, activation reagent amount, activation temperature on morphology, structure and electrochemical performance were systematically studied. Under the optimized conditions, the carbon composites demonstrated remarkable electrochemical performances as supercapacitor electrodes with an outstanding specific capacitance of 340 F g−1 at a current density of 0.5 A g−1, and retained 203 F g−1 at a high current density of 50 A g−1 in 6 mol L−1 KOH solution. Moreover, the cycling stability was considerably efficient without any decay after 2000 cycles. The outstanding supercapacitor performance was considered to be related to the large surface area, appropriate hierarchical pore structure, N-doping and good electrical conductivity of the RGO@HTC. The electrochemical performance coupled with a facile and low-cost preparation procedure ensured the resulting RGO@HTC as promising electrode materials for supercapacitor applications.

Enhancement of capacitive deionization capacity of hierarchical porous carbon

Capacitive deionization (CDI) has attracted huge interest as an energy-efficient and eco-friendly desalination strategy. Its development is presently limited due to the relatively low CDI capacitances of carbon materials. Herein, hierarchical porous carbon materials (HPCs) derived from ethylenediaminetetraacetic acid (EDTA) upon annealing were used, which showed impressive CDI performance with a maximum desalination capacity of 34.27 mg g−1 in 40 mg L−1 NaCl aqueous solution. Such capability was attributed to the appropriate hierarchical pore structure, high specific surface area (2185.71 m2 g−1), large pore volume (1.368 cm3 g−1) and reasonable graphitization degree, which were also confirmed by the high specific capacitances of 182 F g−1 in 1 mol L−1 NaCl and 260 F g−1 in 6 mol L−1 KOH. Since the physisorption capacity was nearly 0, and the regeneration process was facile and complete, such economical HPCs materials show potential for practical desalination applications in the future. Moreover, the HPCs electrodes presented ion selectivity in competitive multi-ionic solutions by kinetic behavior difference or static capacitance difference.

Phosphorus oxoanion-intercalated layered double hydroxides for high-performance oxygen evolution

Rational design and controlled fabrication of efficient and cost-effective electrodes for the oxygen evolution reaction (OER) are critical for addressing the unprecedented energy crisis. Nickel–iron layered double hydroxides (NiFe-LDHs) with specific interlayer anions (i.e. phosphate, phosphite, and hypophosphite) were fabricated by a co-precipitation method and investigated as oxygen evolution electrocatalysts. Intercalation of the phosphorus oxoanion enhanced the OER activity in an alkaline solution; the optimal performance (i.e., a low onset potential of 215 mV, a small Tafel slope of 37.7 mV/dec, and stable electrochemical behavior) was achieved with the hypophosphite-intercalated NiFe-LDH catalyst, demonstrating dramatic enhancement over the traditional carbonate-intercalated NiFe-LDH in terms of activity and durability. This enhanced performance is attributed to the interaction between the intercalated phosphorous oxoanions and the edge-sharing MO6 (M = Ni, Fe) layers, which modifies the surface electronic structure of the Ni sites. This concept should be inspiring for the design of more effective LDH-based oxygen evolution electrocatalysts.