The ever worsening energy depletion and global warming issues call for not only urgent development of clean alternative energies and emission control of global warming gases, but also more advanced energy storage and management devices. Supercapacitors, offering transient but extremely high powers, are probably the most important next generation energy storage device. [1] To boost the specific capacitance of supercapacitors, the specific surface area of the electrode materials needs to be as high as possible to promote the electric double-layer capacitances and to accommodate a large amount of superficial electroactive species to participate in faradaic redox reactions. In addition, suitable pore sizes, 2-5 nm, of the porous electrode materials are critical to ease the mass transfer of electrolytes within the pores for fast redox reactions and double-layer charging/discharging. [2][3][4][5] Aerogels are a class of mesoporous materials possessing highly specific surface areas and porosities, [6] from which promising applications in a wide range of areas have been investigated. [7][8][9][10] They are composed of 3D networks of nanoparticles with an average pore size of several nanometers, adjustably falling within the optimal pore sizes of 2-5 nm. Consequently, aerogels are a promising candidate for supercapacitor applications.As to the electrode material, electroactive materials possessing multiple oxidation states/structures that enable rich redox reactions for pseudocapacitance generation are desirable for supercapacitors. Transition metal oxides are such a class of materials that have drawn extensive and intensive research attention in recent years. Among them, RuO 2 is the most prominent one with a specific capacitance as high as 1580 F g À1 , [11] probably the highest ever reported. The commercialization of RuO 2 based supercapacitors, however, is not promising because of the high cost and rareness of Ru. Spinel nickel cobaltite (NiCo 2 O 4 ) is a low-cost, environmentally friendly transition metal oxide, which has been employed in electrocatalytic water splitting (oxygen evolution) [12][13][14] and lithium ion batteries. [15,16] Its application in supercapacitors, however, received much less attention. [16,17] Nickel cobaltite has been reported to possess a much better electronic conductivity, at least two orders of magnitude higher, and higher electrochemical activity than those of nickel oxides and cobalt oxides.[18] It is expected to offer richer redox reactions, including contributions from both nickel and cobalt ions, than the two corresponding single component oxides and is a potential cost-effective alternative for RuO 2 .Based on the above considerations, one would expect nickel cobaltite aerogels, with anticipated good electronic conductivity, low diffusion resistance to protons/cations, easy electrolyte penetration, and high electroactive areas to be a promising candidate for the construction of next-generation, ultrahighperformance supercapacitors. Traditionally, aerogels are prepared with sol-gel...

A Schottky barrier can be formed at the interface between a metal electrode and a semiconductor. The current passing through the metal-semiconductor contact is mainly controlled by the barrier height and barrier width. In conventional nanodevices, Schottky contacts are usually avoided in order to enhance the contribution made by the nanowires or nanotubes to the detected signal. We present a key idea of using the Schottky contact to achieve supersensitive and fast response nanowire-based nanosensors. We have illustrated this idea on several platforms: UV sensors, biosensors, and gas sensors. The gigantic enhancement in sensitivity of up to 5 orders of magnitude shows that an effective usage of the Schottky contact can be very beneficial to the sensitivity of nanosensors.

A new single nanowire based nanosensor is demonstrated for illustrating its ultrahigh sensitivity for gas sensing. The device is composed of a single ZnO nanowire mounted on Pt electrodes with one end in Ohmic contact and the other end in Schottky contact. The Schottky contact functions as a "gate" that controls the current flowing through the entire system. By tuning the Schottky barrier height through the responsive variation of the surface chemisorbed gases and the amplification role played by the nanowire to Schottky barrier effect, an ultrahigh sensitivity of 32,000% was achieved using the Schottky contacted device operated in reverse bias mode at 275 degrees C for detection of 400 ppm CO, which is 4 orders of magnitude higher than that obtained using an Ohmic contact device under the same conditions. In addition, the response time and reset time have been shortened by a factor of 7. The methodology and principle illustrated in the paper present a new sensing mechanism that can be readily and extensively applied to other gas sensing systems.