Jinliang Yuan

Fabrication of Binder-Free Pencil-Trace Electrode for Lithium-Ion Battery: Simplicity and High Performance

A binder-free and solvent-free pencil-trace electrode with intercalated clay particles (mainly SiO2) is prepared via a simple pencil-drawing process on grinded Cu substrate with rough surface and evaluated as an anode material for lithium-ion battery. The pencil-trace electrode exhibits a high reversible capacity of 672 mA h g(-1) at 100 mA g(-1) after 100 cycles, which can be attributed to the unique multilayered graphene particles with lateral size of few micrometers and the formation of LixSi alloys generated by interaction between Li(+) and an active Si produced in the electrochemical reduction of nano-SiO2 in the clay particles between the multilayered graphene particles. The multilayered graphene obtained by this process consists of 1 up to 20 and occasionally up to 50 sheets and thus can not only help accommodating the volume change and alleviating the structural strain during Li ion insertion and extraction but also allow rapid access of Li ions during charge-discharge cycling. Drawing with a pencil on grinded Cu substrate is not only very simple but also cost-effective and highly scalable, easily establishing graphitic circuitry through a solvent-free and binder-free approach.

Urine to highly porous heteroatom-doped carbons for supercapacitor: A value added journey for human waste

Obtaining functionalized carbonaceous materials, with well-developed pores and doped heteroatoms, from waste precursors using environmentally friendly processes has always been of great interest. Herein, a simple template-free approach is devised to obtain porous and heteroatom-doped carbon, by using the most abundant human waste, “urine”. Removal of inherent mineral salts from the urine carbon (URC) makes it to possess large quantity of pores. Synergetic effect of the heteroatom doping and surface properties of the URC is exploited by carrying out energy storage application for the first time. Suitable heteroatom content and porous structure can enhance the pseudo-capacitance and electric double layer capacitance, eventually generating superior capacitance from the URC. The optimal carbon electrode obtained particularly at 900 °C (URC-900) possesses high BET surface area (1040.5 m2g−1), good conductivity, and efficient heteroatom doping of N, S, and P, illustrating high specific capacitance of 166 Fg−1 at 0.5 Ag−1 for three-electrode system in inorganic electrolyte. Moreover, the URC-900 delivers outstanding cycling stability with only 1.7% capacitance decay over 5,000 cycles at 5 Ag−1. Present work suggests an economical approach based on easily available raw waste material, which can be utilized for large-scale production of new age multi-functional carbon nanomaterials for various energy applications.

Numerical simulation of two-phase flow and heat transfer in a composite duct

In this work, a three-dimensional computational method has been further developed for a composite duct, to analyze water phase change and liquid water saturation level, two-phase flow and heat transfer in a multi-component mixture. The duct under consideration consists of a flow duct, porous layer and solid structure. Advanced boundary conditions are applied in the analysis, concerning the thermal boundary conditions, mass consumption and generation appearing on the active surface, interfacial conditions between the flow duct and the porous layer etc. The coupled effects of species composition, mass transfer, phase change/balance have been taken into account. It has been found that the two-phase flow is sensitive to the operating parameters, and liquid water transport is dominated by diffusion in the porous layer, based on its mass composition gradient. (Less)

Numerical investigation of transport phenomena in high temperature proton exchange membrane fuel cells with different flow field designs

ABSTRACT In this work, a three-dimensional, non-isothermal, steady-state model for high temperature proton exchange membrane fuel cells with phosphoric acid polybenzimidazole membrane has been developed using computational fluid dynamics. The importance of the gas flow field design on the transport characteristics and cell performance is revealed by solving the mass, momentum, species, energy, and charge conservation equations. The numerical results show that the best cell performance is provided by the fuel cell with serpentine flow channel flow field. However, the pressure drop is also very high due to the large length of the serpentine channel. In addition, the velocity, oxygen mass fraction, and temperature distributions are unevenly distributed over the entire active area of the fuel cell having straight channels with small manifolds, especially at low cell voltages when a large amount of oxygen is required. The cell performance and durability can be significantly affected by the uniformity of the reactants within the fuel cell. It is suggested that the flow field configurations must be optimized to obtain uniform distributions of the reactants, maximize the cell performance, and minimize the pressure drop penalty. The present results provide detailed information about transport characteristics within fuel cells and give guidelines for design and manufacturing of current collectors.

Analysis of compact heat exchangers as an intercooler in pemfc systems

In Proton Exchange Membrane Fuel Cell (PEMFC) systems, an intercooler contributes to proper thermal management of the reactant air into the cathode. However, the structure/performance of it is not clear yet. In this paper, two case studies concerning an intercooler in a 100 kW PEMFC system are carried out. Plate-fin and tube-fin heat exchangers are analyzed as the intercooler, in terms of volume, pressure drop and weight, The e-NTU method is used. As general characteristics of the intercooler, the volume is increased with system operating pressure, while the pressure drop is decreased due to the volume expansion. The plate-fin intercooler contributes to the weight reduction of the system because aluminum is used. However, at the high operating pressure, space consumption is large. The tube-fin intercooler contributes to the volume reduction because the coolant is a liquid. However, the usage of stainless steel contributes to weight increase. The tube-fin intercooler in aluminum may contribute to space and weight reduction. However, a liquid coolant, which is proper for the PEMFC stack cooling without corrosion of aluminum, is needed. Copyright