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Review on progress and challenges of the power generation systems at micro-scales

Chen J. J., Xu D. G.

International Letters of Chemistry, Physics and Astronomy

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2015

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Vol. 47

185--198

EN

The miniaturization of electro-mechanical devices, and the resulting need for micro-power generation (milliwatts to watts) with low weight, long life devices, has led to the recent development of the field of micro-scale combustion and power generation. The primary objective of this new field is to leverage the high energy density of fuels, specifically liquid hydrocarbon fuels relative to batteries and all other energy storage devices other than nuclear fission, fusion or decay. Some brief scaling arguments are given in this work, and more detailed efforts are referred. A brief introduction to several of the fabrication techniques is presented in this work. Hydrogen-based and some preliminary specialty fuel micro-fuel cells have been successfully developed, and there is a need to develop reliable reformers (or direct conversion fuel cells) for liquid hydrocarbons so that the fuel cells become competitive with the batteries. In this work, the technological issues related to micro-scale combustion and the development of thermochemical devices for power generation will be discussed. Some of the systems currently being developed will be presented, ongoing critical study issues under investigation, and other potential areas of development discussed. Comments regarding the opportunities and limitations of each of the techniques are also presented where applicable.

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Recent development and applications in electrodes for URFC

Chen J. J., Xu D. G.

International Letters of Chemistry, Physics and Astronomy

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2015

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Vol. 47

165--177

EN

The design of electrodes for URFC (unitised regenerative polymer electrolyte fuel cells) requires a delicate balancing of transport media. Gas transport, electrons and protons must be carefully optimised to provide efficient transport to and from the electrochemical reaction sites. This review is a survey of recent literature with the objective to identify common components and design and assembly methods for URFC electrodes, focusing primarily on the development of a better performing bifunctional electrocatalyst for the oxygen reduction and water oxidation. Advances in unitised regenerative fuel cells study have yielded better performing oxygen electrocatalysts capable of improving energy efficiency with longer endurance and less performance degradation over time. Fuel cells using these electrocatalyst have a possible future as a source of energy.

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Progress and Challenges in the Direct Carbon Fuel Cell Technology

Chen J. J., Gao X. H., Yan L. F., Xu D. G.

International Letters of Chemistry, Physics and Astronomy

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2015

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Vol. 49

109--129

EN

Fuel cells are under development for a range of applications for transport, stationary and portable power appliances. Fuel cell technology has advanced to the stage where commercial field trials for both transport and stationary applications are in progress. Direct Carbon Fuel Cells (DCFC) utilize solid carbon as the fuel and have historically attracted less investment than other types of gas or liquid fed fuel cells. However, volatility in gas and oil commodity prices and the increasing concern about the environmental impact of burning heavy fossil fuels for power generation has led to DCFCs gaining more attention within the global study community. A DCFC converts the chemical energy in solid carbon directly into electricity through its direct electrochemical oxidation. The fuel utilization can be almost 100% as the fuel feed and product gases are distinct phases and thus can be easily separated. This is not the case with other fuel cell types for which the fuel utilization within the cell is typically limited to below 85%. The theoretical efficiency is also high, around 100%. The combination of these two factors, lead to the projected electric efficiency of DCFC approaching 80% - approximately twice the efficiency of current generation coal fired power plants, thus leading to a 50% reduction in greenhouse gas emissions. The amount of CO2 for storage/sequestration is also halved. Moreover, the exit gas is an almost pure CO2 stream, requiring little or no gas separation before compression for sequestration. Therefore, the energy and cost penalties to capture the CO2 will also be significantly less than for other technologies. Furthermore, a variety of abundant fuels such as coal, coke, tar, biomass and organic waste can be used. Despite these advantages, the technology is at an early stage of development requiring solutions to many complex challenges related to materials degradation, fuel delivery, reaction kinetics, stack fabrication and system design, before it can be considered for commercialization. This paper, following a brief introduction to other fuel cells, reviews in detail the current status of the direct carbon fuel cell technology, recent progress, technical challenges and discusses the future of the technology.