Yinshi Li

High performance of a carbon supported ternary PdIrNi catalyst for ethanol electro-oxidation in anion-exchange membrane direct ethanol fuel cells

In this paper, we report the synthesis of a carbon supported ternary PdIrNi catalyst for the ethanol oxidation reaction in anion-exchange membrane direct ethanol fuel cells (AEM DEFCs). We demonstrate that the use of the ternary PdIrNi catalyst at the anode of an AEM DEFC can increase the peak power density by more than 122% as compared with the use of the monometallic Pd catalyst, 69% as compared with the use of the bimetallic PdIr catalyst, and 44% as compared with the use of the bimetallic PdNi catalyst. Cyclic voltammetry and chronopotentiometry analyses prove that the ternary PdIrNi catalyst is catalytically much more active and more stable than the monometallic Pd catalyst and the bimetallic PdIr and PdNi catalysts.

Charge carriers in alkaline direct oxidation fuel cells

Contrary to conventional wisdom, this study demonstrates that the main charge carrier of alkaline direct oxidation fuel cells (DOFCs) running on ethanol with a cation exchange membrane (typically Nafion) is OH− ions, rather than Na+ ions.

Layer reduction method for fabricating Pd-coated Ni foams as high-performance ethanol electrode for anion-exchange membrane fuel cells

An ideal electrode architecture that boosts the performance of anion-exchange membrane direct liquid fuel cells needs the electrode design to meet all the requirements of electrochemical kinetics and mass and charge transport characteristics. In this regard, here we propose a facile, well-controlled, and binder-free layer reduction method for preparing a three-dimensional foam electrode, which enables the catalytic particles to be directly reduced on the surface of the metal foam. This innovative layer reduction method not only avoids the formation of large catalytic aggregation, but also promises a thin and porous catalyst film that presents a sponge-like morphology uniformly coated onto the skeleton, thus both improving the electrochemical kinetics and enhancing the mass and charge transport of species. The results demonstrate that the application of the layer-reduced Pd/Ni foam electrode in an anion-exchange membrane direct ethanol fuel cell enables a peak power density and the maximum current density as high as 164 mW cm−2 and 1.34 A cm−2 at 60 °C, respectively, which are 1.03 and 1.16 times higher than those of the conventional design.

Hydroxide Self-Feeding High-Temperature Alkaline Direct Formate Fuel Cells

Conventionally, both the thermal degradation of the anion-exchange membrane and the requirement of additional hydroxide for fuel oxidation reaction hinder the development of the high-temperature alkaline direct liquid fuel cells. The present work addresses these two issues by reporting a polybenzimidazole-membrane-based direct formate fuel cell (DFFC). Theoretically, the cell voltage of the high-temperature alkaline DFFC can be as high as 1.45 V at 90 °C. It has been demonstrated that a proof-of-concept alkaline DFFC without adding additional hydroxide yields a peak power density of 20.9 mW cm-2 , an order of magnitude higher than both alkaline direct ethanol fuel cells and alkaline direct methanol fuel cells, mainly because the hydrolysis of formate provides enough OH- ions for formate oxidation reaction. It was also found that this hydroxide self-feeding high-temperature alkaline DFFC shows a stable 100 min constant-current discharge at 90 °C, proving the conceptual feasibility.

A Sodium-Ion-Conducting Direct Formate Fuel Cell: Generating Electricity and Producing Base

A barrier that limits the development of the conventional cation-exchange membrane direct liquid fuel cells (CEM-DLFCs) is that the CEM-DLFCs need additional base to offer both alkaline environment and charge carriers. Herein, we propose a Na+ -conducting direct formate fuel cell (Na-DFFC) that is operated in the absence of added base. A proof-of-concept Na-DFFC yields a peak power density of 33 mW cm-2 at 60 °C, mainly because the hydrolysis of sodium formate provides enough OH- and Na+ ions, proving the conceptual feasibility. Moreover, contrary to the conventional chlor-alkali process, this Na-DFFC enables to generate electricity and produce NaOH simultaneously without polluting the environment. The Na-DFFC runs stably during 13 hours of continuous operation at a constant current of 10 mA, along with a theoretical production of 195 mg NaOH. This work presents a new type of electrochemical conversion device that possesses a wide range of potential applications.

A molecular dynamics study on growth of condensation film on a solid surface

A molecular dynamics simulation for the condensation of vapour on a solid wall was carried out to study the growth of the condensation film. The results show that with the increase in the vapour temperature, the temperature jump and the temperature gradient increase, however, the depth of the potential well and the absolute value of the potential force in the interfacial region decrease. The film growth rate is about 0.96 m/s at 120 K, and will increase nearly linearly with increasing vapour temperature. In addition, the mass flux also increases because larger temperature difference has strengthened the condensation process.

A Molecular Dynamics Study on Obstructed Flow Around Single and Two Paratactic Circular Cylinders

Obstructed flow around single and two paratactic circular cylinders were investigated with two-dimensional molecular dynamics simulation (MDS) methods in the view of discrete particles. The transient and time-averaged profiles of streamline and density were obtained in order to analyze the characteristics of the wake flow. For single cylinder case, different flow patterns, i.e. Stokes flow, steady vortices flow, periodic vortices-shedding flow with the Karman vortex street and supersonic flow, were divided based on Reynolds number (Re), 4 62 respectively. For two paratactic cylinders case, different flow patterns, namely periodic vortices-shedding flow, periodic vortices-shedding flow with gap-flow, bistable flow and synchronized vortex-shedding flow, were observed with different center-to-center pitch ratios (D* /d* ), D* /d* = 1.0, 1.0 1.8 respectively. The results show qualitative or quantitative agreement with those obtained from experiments and other MDS and indicate that most macroscopic obstructed flow patterns still exist even in nanoscale.Copyright

System Design and Performance in Alkaline Direct Ethanol Fuel Cells

Fuel cells that convert the chemical energy stored in a fuel into an electrical energy by electrochemical reactions have been recognized as one of the most promising technologies for the clean energy industry of the future, especially for alkaline direct ethanol fuel cells (DEFCs), because ethanol is less toxic than methanol and can be massively produced from agricultural products or biomass, in addition to the advantage of high specific energy and quicker electro-kinetics of both the ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) in alkaline media. A considerable amount of effort has been devoted to the development of alkaline membranes and electro-catalystsin alkaline DEFCs, including synthesis of anion-exchange membrane and electro-catalysts, and the mechanism study of both the anodic EOR and cathodic ORR. For given materials, the improvement of the cell performance, however, depends mainly on the system design. This chapter provides a brief review of the development of alkaline DEFCs from the point of view of the system.

Challenges and Perspectives in Alkaline Direct Ethanol Fuel Cells

Alkaline direct ethanol fuel cells (DEFCs) that have the quicker electro-kinetics of both the ethanol oxidation reaction and oxygen reduction reaction can yield much better performance than acid direct ethanol fuel cells, even with low-cost non-Pt metals as the electro-catalysts. The liquid-feed alkaline DEFC also possesses the advantages that a direct methanol fuel cell (DMFC) has, including simpler system structures, and fast refueling. Although appealing, many challenges in both material synthesis and system design have to be overcome before extensively commercializing the alkaline DEFCs. In view of these facts, there exists the need to improve the materials and design the novel systems, achieving the high cell performance and durability. This chapter emphasizes on challenges and perspectives in the ethanol electro-oxidation, anion-exchange membrane and the system designs.

Study on nanoscale obstructed flow with Molecular Dynamics Simulation method

Obstructed flow around single cylinder and two paratactic cylinders in nanoscale were investigated in the view of discrete particles. Transient and temporal-averaged flow and density fields were obtained to analyse the wake flow. For single cylinder case, Stokes flow, steady vortex flow, periodic vortex-shedding flow with the Karman vortex street and supersonic flow were distinguished based on Re. For two paratactic cylinders case, periodic vortex-shedding flow, periodic vortex-shedding flow with gap-flow, bistable flow and synchronised vortex-shedding flow were observed with different centre-to-centre pitch ratios. Despite of some special characteristics, the results indicate most macroscopic flow patterns still exist in nanoscale.