Xi'an Jiaotong University

About: Xi'an Jiaotong University is a education organization based out in Xi'an, China. It is known for research contribution in the topics: Heat transfer & Dielectric. The organization has 85440 authors who have published 99682 publications receiving 1579683 citations. The organization is also known as: '''Xi'an Jiaotong University''' & Xi'an Jiao Tong University.

Atomic-Scale CoOx Species in Metal-Organic Frameworks for Oxygen Evolution Reaction

Abstract: The activity of electrocatalysts strongly depends on the number of active sites, which can be increased by downsizing electrocatalysts. Single-atom catalysts have attracted special attention due to atomic-scale active sites. However, it is a huge challenge to obtain atomic-scale CoOx catalysts. The Co-based metal-organic frameworks (MOFs) own atomically dispersed Co ions, which motivates to design a possible pathway to partially on-site transform these Co ions to active atomic-scale CoOx species, while reserving the highly porous features of MOFs. In this work, for the first time, the targeted on-site formation of atomic-scale CoOx species is realized in ZIF-67 by O-2 plasma. The abundant pores in ZIF-67 provide channels for O-2 plasma to activate the Co ions in MOFs to on-site produce atomic-scale CoOx species, which act as the active sites to catalyze the oxygen evolution reaction with an even better activity than RuO2.

A Flexible Fiber-Based Supercapacitor-Triboelectric-Nanogenerator Power System for Wearable Electronics.

Abstract: A flexible self-charging power system is built by integrating a fiber-based supercapacitor with a fiber-based triboelectric nanogenerator for harvesting mechanical energy from human motion. The fiber-based supercapacitor exhibits outstanding electrochemical properties, owing to the excellent pseudocapacitance of well-prepared RuO2 ·xH2 O by a vapor-phase hydrothermal method as the active material. The approach is a step forward toward self-powered wearable electronics.

Enhanced cycling stability of hierarchical NiCo2S4@Ni(OH)2@PPy core–shell nanotube arrays for aqueous asymmetric supercapacitors

Abstract: In this article, a novel electrode of NiCo2S4@Ni(OH)2@polypyrrole nanotube arrays supported on nickel foam is fabricated through a facile method. Due to the superior electronic conductivity of the shell material polypyrrole (PPy) and the high pseudocapacitance of Ni(OH)2 together with the short ion transport pathway of NiCo2S4 nanotube arrays, the obtained core–shell NiCo2S4@Ni(OH)2@PPy shows an enhanced pseudocapacitive performance of about 9.1125 F cm−2 at a current density of 5 mA cm−2, which is nearly three times higher than that of the pristine NiCo2S4 sample (3.1875 F cm−2). The kinetic analysis reveals the diffusion controlled faradaic characteristic of NiCo2S4@Ni(OH)2@PPy (43.57% capacitive contribution). Moreover, an asymmetric supercapacitor is successfully assembled with NiCo2S4@Ni(OH)2@PPy as the positive electrode and active carbon (AC) as the negative electrode. The NiCo2S4@Ni(OH)2@PPy//AC device exhibits a relatively high energy density of 34.67 W h kg−1 at a power density of 120.127 W kg−1 and excellent cycling performance (about 98.87% capacitance retention over 30 000 cycles). The results show that the NiCo2S4@Ni(OH)2@PPy core–shell nanotube array is a promising electrode material for high performance supercapacitor applications.

Distributed Beamforming for Physical-Layer Security of Two-Way Relay Networks

Abstract: In this paper, we address the security of a two-way relay network in the presence of an eavesdropper, where each node is only equipped with single antenna. We propose two-phase distributed analog network coding, or distributed beamforming and power allocation to enhance the secrecy sum rate of the data exchange. In the first phase, the two terminals broadcast their information data simultaneously to all the relay nodes. In the second phase, three different security schemes are proposed: optimal beamforming, null-space beamforming, and artificial noise beamforming. In the first scheme, the objective is to achieve the maximum secrecy sum rate of the two terminals. Mathematically, the objective function is difficult to optimize. In the second scheme, we maximize the total information exchanged while we eliminate the information leakage completely, subject to the total transmission power constraint. We show that the problem has a unique and global optimum, which can be solved using bisection method. When the instantaneous channel state information of the eavesdropper is not available, we propose an artificial noise beamforming in the third scheme. We minimize the information transmission power so that the artificial noise power is maximized to eliminate information leakage, under the constraints of quality of service (QoS) required by terminals. It is a second-order convex cone programming (SOCP) problem, thus can be efficiently solved using interior point methods. Numerical results are provided and analyzed to show the properties and efficiency of the proposed designs.