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Microfluidic fuel cell (MFC) is a burgeoning category of micro fuel cell technology based on laminar flow electrolytes. The merits of MFC, such as the absence of membrane electrolyte, flexible reactants selection, and high electrolyte conductivity, have been attracting researchers to explore this frontier area over the past two decades. However, realizing practical applications of MFCs remains a tremendous challenge. Many research works have been done to expedite research progress and obtain results reflecting inner mechanism via computational modeling and simulation, the general procedure of which is introduced in this paper. These studies primarily investigate the effects of various geometrical and operational parameters on diverse cell performance metrics, such as open-circuit voltage, current and power densities, and fuel utilization efficiency. However, contradictory outcomes and conclusions may arise due to disparities in the structural and parametric characteristics among different MFC models. In this regard, this review comprehensively summarizes prior computational modeling studies on MFC technology, with specific emphasis on different cell components including microchannels, inlets and outlets, electrodes, etc., as well as effects of different operational conditions encompassing electrolyte input, cell vibration, gas bubbling, and gravity. In addition, other related studies involving paper-based MFCs, cell stacking, and twin models are also introduced. Lastly, the future research perspective on MFC computational modeling is proposed, including potential structural innovations and modeling methods. This review paper shows the big puzzle of MFC modeling, the missing part of which is worthy of further study in the future. [Display omitted] • A comprehensive review on microfluidic fuel cell modeling is presented. • Governing equations and modeling method for microfluidic fuel cell are introduced. • Studies on different cell configurations and operational conditions are introduced. • Studies on paper-based fuel cell, fuel cell stack and twin model are also presented. • Future research directions for microfluidic fuel cell modeling are proposed finally. [ABSTRACT FROM AUTHOR]

Since its first appearance in 2002, microfluidic fuel cell has received great attention in the past two decades, which is mainly targeted at its use in portable electronics. This micro fuel cell technology utilizes microfluidic flows as electrolyte instead of conventional polymer membranes. To date, various fuels have been utilized in it, such as vanadium species, hydrogen, hydrocarbons, hydrogen peroxide, borohydride and nitrogenous materials, each of which has its specific merits and demerits. To optimize its power output and fuel utilization, innovative cell structures and advanced catalysts have been continuously developed for different fuels, with remarkable improvements achieved. The power output can be elevated from several mW cm−2 to several W cm−2 at room temperature, while the fuel utilization per single pass can reach 100% by using 3D flow-through electrodes. Also, investigations in recent years have shown that microfluidic fuel cell stacking increases the working voltage. In addition to cells with plastic channel, novel cell designs based on cellulose paper and fabric materials have also been proposed; apart from being lightweight, they are also free from pumping. These innovative cell designs represent a promising route for achieving real applications in areas such as medical diagnostic, wearable healthcare and smart logistics. As for the conventional plastic cells, they are currently less competitive against batteries and other fuel cells because of the extra pumping requirement, which should be resolved in future by developing passive pumps instead. Alternatively, they can be applied in specific circumstances where the extra pumping loss is tolerable. • Microfluidic fuel cells with different types of fuels are summarized and compared. • Various flow configurations and electrode structures are reviewed in detail. • Stacking efficiency is compared among different microfluidic fuel cell stacks. • Paper-based and fabric-based microfluidic fuel cells without pumping are introduced. • An outlook on their future development and application is provided. [ABSTRACT FROM AUTHOR]

Fuel cells convert the chemical energy of fuels directly into electricity. They are not limited by the Carnot efficiency granting theoretical efficiency of up to 100% as per Gibbs free energy and enthalpy of formation ratio. Direct carbon fuel cells (DCFCs) electrochemically convert the chemical energy of solid carbon-rich fuels directly into electricity with efficiencies approaching 90%. Once coupled with a high-grade solid carbon-producing solar methane cracking reactor, DCFCs would essentially produce a pure CO 2 flue stream that is nearly capture-ready. Unlike most fuel cell types that employ gaseous fuels, DCFCs can utilize high-grade carbon derived from solar methane cracking reactors, allowing for nearly complete fuel utilization with the entropy change. Thus the reversible heat of the cell reaction is practically zero eliminating the need for cooling and heating in steady-state operation. Therefore, they have the potential to leapfrog the technical evolution process towards achieving clean power generation with dramatically higher efficiencies and lower emissions by producing a nearly pure CO 2 flue stream that is practically capture-ready. However, despite their advantages, DCFCs experience a complication with respect to solid carbon fuel impurities and ash content of the feedstock. This paper provides a concise overview of recent advances in DCFC technology and elaborates on the potential of high-grade carbon produced from solar methane cracking for use as a fuel in DCFCs. The paper demonstrates a promising system coupling DCFCs with solar methane cracking reactors and lays out the challenges of the proposed system, including carbon agglomeration, deposition, and solar reactor clogging problems. • Review of recent advances in DCFCs. • Discussion of the potential of solar thermally produced carbon for use in DCFCs. • Review of the production of carbon black via solar methane cracking. • A new cleaning mechanism to reduce carbon deposition and clogging. • A novel hybrid DCFC-solar methane cracking system for clean power generation. [ABSTRACT FROM AUTHOR]

The current editorial summarized some of the scientific works presented in the Sustainable Energy and Environmental Protection (SEEP) conference-held at the University of the West of Scotland, UK, 2018. The selected work was directly related to the scope of the Renewable, Sustainable Energy Reviews (RSER) journal. During the conference activities, experts from all around the world in the subjects of: renewable energy, climate change, optimization, and economics presented and discussed the progress made in renewable energy sources, as well as the new strategies for protecting the environment from the hazards connected with fossil fuel utilization. The methods presented in the conference focused on several directions: the development of efficient energy conversion systems with low/no environmental impacts; the suggested policies to widespread renewable energies; the restriction in the emission of greenhouse gases, and the recent progresses in CO 2 capture. This editorial focused on the renewable energy developments and their positive effect on the climate change, and briefly summarized the accepted manuscripts in this issue. • Effects of renewable energy on climate change. • Background on the International Conference on Sustainable Energy and Environmental Protection SEEP. • Summary of selected papers of SEEP 2018. [ABSTRACT FROM AUTHOR]

The current editorial summarized some of the scientific works presented in the Sustainable Energy and Environmental Protection (SEEP) conference-held at the University of the West of Scotland, UK, 2018. The selected work was directly related to the scope of the Renewable, Sustainable Energy Reviews (RSER) journal. During the conference activities, experts from all around the world in the subjects of: renewable energy, climate change, optimization, and economics presented and discussed the progress made in renewable energy sources, as well as the new strategies for protecting the environment from the hazards connected with fossil fuel utilization. The methods presented in the conference focused on several directions: the development of efficient energy conversion systems with low/no environmental impacts; the suggested policies to widespread renewable energies; the restriction in the emission of greenhouse gases, and the recent progresses in CO 2 capture. This editorial focused on the renewable energy developments and their positive effect on the climate change, and briefly summarized the accepted manuscripts in this issue. • Effects of renewable energy on climate change. • Background on the International Conference on Sustainable Energy and Environmental Protection SEEP. • Summary of selected papers of SEEP 2018. [ABSTRACT FROM AUTHOR]