1- Introduction

2- Electrode materials

3- Mechanisms of electron transport

4- Field standardisation and comparison techniques

5- Conclusions

References

Abstract

Research into alternative renewable energy generation is a priority, due to the ever-increasing concern of climate change. Microbial fuel cells (MFCs) are one potential avenue to be explored, as a partial solution towards combating the over-reliance on fossil fuel based electricity. Limitations have slowed the advancement of MFC development, including low power generation, expensive electrode materials and the inability to scale up MFCs to industrially relevant capacities. However, utilisation of new advanced electrode-materials (i.e. 2D nanomaterials), has promise to advance the field of electromicrobiology. New electrode materials coupled with a more thorough understanding of the mechanisms in which electrogenic bacteria partake in electron transfer could dramatically increase power outputs, potentially reaching the upper extremities of theoretical limits. Continued research into both the electrochemistry and microbiology is of paramount importance in order to achieve industrial-scale development of MFCs. This review gives an overview of the current field and knowledge in regards to MFCs and discusses the known mechanisms underpinning MFC technology, which allows bacteria to facilitate in electron transfer processes. This review focusses specifically on enhancing the performance of MFCs, with the key intrinsic factor currently limiting power output from MFCs being the rate of electron transfer to/from the anode; the use of advanced carbon-based materials as electrode surfaces is discussed.

Introduction

Energy generation, storage and consumption are topics that are increasingly prevalent within modern research fields and are of global interest and importance [1,2]. Research into alternative renewable energy generation sources are increasing exponentially, with vast research showing promising results, in an abundance of areas including: solar [3], wind [4], tidal [5], geothermal [6] and biomass energy generation (Fig. 1) [7,8]. Currently no individual renewable energy source has the ability to compete with and replace the conventional fossil-fuel based energy generation approach, however, combining renewable energy sources such as, solar-wind hybrids and/or solar-hydrogen fuel cells may be alternative routes to be explored [9,10]. One potential alternative energy source is the use of microbial fuel cells (MFCs). MFCs follow a similar concept to traditional fuel cells (Fig. 2). However, MFCs utilise the bio-catalytic capabilities of viable microorganisms and are capable of using a range of organic fuel sources, by converting the energy stored in the chemical bonds, to generate an electrical current instead of relying for example, on the use of metal catalysts [1]. Microorganisms, such as bacteria, can generate electricity by utilising organic matter and biodegradable substrates such as wastewater, whilst also accomplishing biodegradation/treatment of biodegradable products, such as municipal wastewater [1,11]. Table 1 provides an overview of the current literature of MFCs. Clearly, significant attention has been given to MFCs cells due to their ambient operating conditions (e.g. utilisation at low temperatures) and a variety of biodegradable substrates as fuel. This review aims to highlight the current understanding of MFCs, whilst giving a thorough overview of the field. Particular emphasis is placed upon the fundamentals of MFC technologies, electrode materials, mechanism of electron transport and field standardisation.

Introduction

Model development

Model validation

Parametric study

Conclusion

References

Abstract

Fuel cell vehicles offer significant sustainability benefits by eliminating tailpipe emissions, increasing powertrain efficiency, and utilizing hydrogen that can be supplied from various sources including renewables. A pressure regulator in the hydrogen storage system on a fuel cell vehicle is an important component to ensure that the hydrogen delivery to the fuel cell stack meets the pressure and temperature requirements. A validated model of the regulator can be used to support the product design and optimization of the operating strategy. In this work, a pressure regulator model has been developed to capture the hydrogen discharge behaviors from the compressed hydrogen tank to the fuel cell stack. The focus of the model is to develop the pressure and temperature relationship at the regulator outlet given the inlet conditions from the storage tank. Besides the ideal-gas based derivation for pressure response, the model has used a constant-enthalpy approach to capture the hydrogen temperature increase associated with the pressure drop due to the Joule–Thomson effect. The model was validated with various testing data including hysteresis and dynamic flow conditions, showing satisfactory agreement. The validated model was then used for parametric studies. The modeling results concluded that the regulator inlet temperature has the strongest influence on raising the outlet temperature, while the regulator inlet pressure is an important factor although secondary to the inlet temperature. The comprehensive regulator modeling developed in this work provides the foundation for assessing and optimizing a key dynamic component in the hydrogen storage system.

Introduction

A fuel cell vehicle is regarded as an important zero-emission alternative that features comparable driving range and refilling time with internal-combustion-engine vehicles [1]. There are many model-based studies to improve the fuel cell system and control in a vehicular application [2e6]. Bao et al. [2,3] developed a dynamic model of fuel cell system to control and optimize the transient behaviors of air supply and hydrogen recirculation considering the mixed effects of gas flow, pressure and humidity. Hatti and Tioursi [4] demonstrated an artificial intelligence technique to control a proton exchange membrane fuel cell system process using a dynamic neural network. The anode recirculation system has been studied with theoretical modeling by Dadvar and Afshari [5], focusing on the optimization of stack and ejector design parameters. The pressure control components play an important role for the desired system performance. Hong et al. [6] presented a control oriented dynamic model for the fuel delivery system with anode recirculation and anode bleeding. Based on the model, a multi-input-multi-output nonlinear state feedback controller along with an optimized output feedback controller is proposed to maintain adequate hydrogen supply and suitable anode hydrogen concentration. However, as a typical simplification, an ideal behavior of reaching desired pressure from hydrogen tank without fluctuation and delay was assumed in these studies. Realistically, the dynamic response of pressure regulators and valves upon load change could influence the performance of system components and stack. For example, the primary flow rate as well as the recirculation ratio of an anode ejector is dependent on the upstream pressure [7]. Insufficient hydrogen supply upon load change could also lead to anode reversal and durability concern such as carbon corrosion [8], besides impacting the stack performance [9] and the accuracy of the abovementioned control strategies. Some component optimization for anode pressuremanagement has been performed.

Hydrogen, as a clean fuel, can provide all the requirements and characteristics of a clean and reliable energy carrier in the long term as a suitable alternative to fossil fuels. In this paper, a power generation system using hydrogen storage has been investigated. For this purpose, 64 photovoltaic modules with area of 2.16 m 2 for each module and 329 PW and 5.5 kW PEM fuel cell and electrolyzer were used in this hybrid system. The day product of hydrogen day has been calculated as 158 kg. The system has been subjected to exergy analysis and, hence the efficiency and destruction of exergy components have been calculated. The annual average electrical production by photovoltaic system is 4850 W. The average annual exergy efficiency of each component including compressor, electrolyzer, fuel cell, and photovoltaic cell has been calculated as 75.9%, 11.2%, 32.8%, and 10.8%, respectively. The energy and exergy efficiencies of the system have been calculated for different days and its average annual values have been obtained 20.4% and 21.8%, respectively. Cost of electricity is 0.127 $/kWh, which is compatible with solar thermal and wind turbine offshore electricity costs. Finally, according to the advanced exergy analysis in all equipment’s except the photovoltaic cell, the highest exergy destruction has been related to exogenous unavoidable.

Introduction

Hydrogen as a clean fuel can be a suitable alternative to fossil fuels due to the fact that it has the characteristics of a clean and safe energy carrier in the long run, in addition to its highest energy per unit (Mitlitsky et al., 1998). The fuel cell and electrolysis unit’s combination has become a new strategy for suppling the required hydrogen to the fuel cell for power generating unit. This combined system is the main source of power and applications in several units (Rekioua et al., 2014). Hydrogen production for the use in fuel cells has been widely investigated. Bilgen (2004) examined various methods to produce hydrogen from renewable energy resource. A similar study was done be Levene et al. (2007) and Smaoui et al. (2015). Integration of photovoltaic (PV) system with fuel cells has been recently investigated for the purpose of hydrogen production (Babayan et al., 2019). A new PV system integrated with polymer electrolyte membrane (PEM) fuel cell using phase change material (PCM) as a storage medium has been presented (Babayan et al., 2019) to produce hydrogen in a filling station of hydrogen. The study showed that the use of PCM resulted in an improvement of energy and exergy efficiencies of the proposed system. Ashari et al. (2012) investigated a system consisting of PEM fuel cell, reformer, burner, and heat exchanger to provide the required electricity, heat and domestic hot water for a residential building. The study revealed that an 8.5 kW fuel cell could meet all the building loads requirements. Residential electricity cost was calculated to be 0.39 $/kWh which is considered to be a high electricity cost. This type of fuel cell was also investigated by Saidi et al. (Saidi et al., 2005a; Saidi et al., 2005b).

1- Introduction

2- Hybrid renewable energy system configuration

3- Control strategies

4- Case description

5- Results: Comparison of Control Strategies

6- Results: effect of MPC control strategy on sizing

7- Conclusions

References

Abstract

The development of Hybrid Renewable Energy Systems (HRES) under the Distributed Generation (DG) paradigm is the support for substantial reduction of CO2 emissions and for greater penetration of renewable energy sources. The performance and reliability of HRES depend on the interaction between demand, generation, storage and the energy management strategy. In this study a comparison between two different control strategies is presented. In particular, a Rule Based Control (RBC) strategy has been compared with a more sophisticated Model Predictive Control (MPC) for the management of an HRES for residential applications.
Results show that a HRES operating in a connected mode has potential to support grid balancing actions giving economic benefits for both end-users and providers. Moreover, the MPC strategy gives a potential reduction of the unbalanced energy exchange with the grid and a more efficient use of the HRES components. The MPC strategy allows thus for a more effective use of renewable sources if compared with a conventional RBC for a Microgrid of same size, thus allowing for a greater penetration of renewable sources into the energy mix, or equivalently, toward downsizing of storage and programmable source subsystems with economic benefits.

Limitations and further research directions

This research helps luxury practitioners to better understand how luxury brands should choose between standardized and localized social media marketing strategies in the Chinese market. We focus on the effectiveness of localized (vs. standardized) celebrity endorsements on social media interactions and perceived brand luxury. However, in addition to celebrity endorsements, there are many other elements in social media commercials, such as language, background, music, art style, and story-telling. All of these elements can be localized or standardized and their effectiveness has not been fully tested. This research has only measured consumers’ perceived brand luxury as the dependent variable. Localized celebrity endorsements may also influence the likability and perceived globalness of brands as well as the intimacy, trust and purchase intention of consumers. An investigation of these mechanisms could contribute to a more comprehensive effects theory of social media marketing strategies and give luxury practitioners more clues in decision-making. In terms of moderating variables, this research has found patriotism to be a significant moderator for consumers’ perceived luxuriousness from localized celebrity endorsements. A search for more moderators (e. g., luxury consumption experience, collectivism) could be a promising direction for future research and prove helpful for luxury brands seeking to engage in precision marketing. This study was conducted in China. Therefore, the findings could not be directly generalized to all the luxury markets. However, our findings should be valid in culturally similar markets like South Korea and Japan. Considering the increasing luxury consumption in these countries, our findings provide insights into the luxury industry. As recently nationalism and patriotism are rising not only in China, but also all around the world, future studies may explore the moderating effect of patriotism in Western countries.

Introduction

Hydrogen fuel cell electric generator characteristics

Method of application

Performance of hydrogen fuel cell electric generator

Discussion of results

Conclusion

References

Abstract

We analyze the feasibility of a novel, hydrogen fuel cell electric generator to provide power with zero noise and emissions for myriad ground based applications. The hydrogen fuel cell electric generator utilizes a novel, scalable apparatus that safely generates hydrogen (H2) on demand according to a novel method, using a controlled chemical reaction between water (H2O) and sodium (Na) metal that yields hydrogen gas of sufficient purity for direct use in fuel cells without risk of contaminating sensitive catalysts. The sodium hydroxide (NaOH) byproduct of the hydrogen producing reaction, is collected within the apparatus for later reprocessing by electrolysis, to recover the Na reactant. The detailed analysis shows that the novel, hydrogen fuel cell electric generator will be capable of meeting the clean power requirements for residential and commercial buildings including single family homes and light commercial establishments under a wide range of geographic and climatic conditions.

Introduction

There is a need in the modern world to provide sustainable means of producing clean energy economically, on a monumental scale. The world’s population is inexorably increasing toward the 10 billion mark and carbon based fossil fuel consumption has increased accordingly, leading to unacceptable levels of air pollution in the major conurbations of both advanced and developing countries [1e4]. Although much of the pollution arises from burning carbon based fossil fuels inside internal combustion engines (ICEs) of motor vehicles and ships, a significant contribution is also made by coal burning thermal power plants used for electricity generation [5,6]. Hydrogen (H2) which is stored in near limitless quantity in sea water is the only alternative fuel that is more abundant and environmentally cleaner with the potential of having a lower cost than nonrenewable carbon based fossil fuels, assuming that engineering challenges related to safe implementation and economical extraction of the hydrogen are overcome. Research on hydrogen storage and generator systems based on water (H2O) remains active. Extensive work has been reported in the scientific literature using sodium borohydride (NaBH4) dissolved in water (H2O) to form an aqueous solution, as a means of storing hydrogen, with its subsequent catalytic decomposition via hydrolysis to generate hydrogen (H2) on demand and sodium borate (NaBO2) byproduct [7e12]. The metal lithium (Li) and its hydrides, namely, lithium hydride (LiH) and lithium borohydride (LiBH4) have been the focus of considerable research for their reactions with water (H2O) for hydrogen generation [13e15].

Sugar cane molasses is most important raw materials for production of alcohols and amino acids in fermentation industries. However, after use of raw materials, a large quantity (8–15 L of wastewater for every liter of alcohol production) of wastewater is discharged which creates serious environmental issues [1]. The molasses based distillery industries wastewater contains high organic matter in terms of Chemical Oxygen Demand (COD: 65,000–13,0000 mg/L), high concentration of minerals, dark brown color, and burnt sugar odor [2]. Several methods includes chemical, electrochemical, biological (aerobic and anaerobic) methods have been exploited for the treatment and disposal of molasses wastewater [3]. Conventionally, an anaerobic digestion method is used for treating such waste and generates methane gas followed by an aerobic treatment prior to disposal [4]. An intensive conventional wastewater treatment system are required to develop an alternative technology which should be reliable, cost effective and also energy recovery. Microbial fuel cell (MFC) is a novel bio-electrochemical system that generates bioelectricity and simultaneously removes pollutant such as COD, color, salinity etc. from wastewater which is one of the most advantageous [5–7]. The MFC consists of biotic anode and abiotic cathode chamber separated by a proton exchange membrane (PEM). The potential developed between metabolic respiration on electron donors and electron acceptors conditions in the anode and cathode generates electricity and water [8]. Earlier, the MFC was operated using pure organic matter such as glucose, acetate and lactose as a substrate to understand the fundamental of process [9,10]. Nowadays more complex substrates (dairy, domestic, starch processing, and paper recycling wastewater etc.) have been used to improve the performance and exploiting the waste into useful product [11–14]. Though, the molasses based distillery wastewater containing high organic matter that provides a great potential source for electricity generation. Additionally, the MFC used sulfide (that generated during the anaerobic process) as a fuel to generate electricity and oxidize sulfide into elemental sulfur [15]. In recent year, the MFC performance was enhanced by varying the operational and design parameters such as reactor configuration, electrode material, electrode distance, pH, microbial communities and substrate concentration etc. [16–19]. Nevertheless, the wastewater feed pH played a significant role on overall performance in dual chamber MFC, because it controls not only bacterial growth and also supports an efficient movement of protons through PEM. Generally, bacteria respond to change internal and external pH by adjusting their activity associated with many different processes, including proton translocation, amino acid degradation, adaptation to acidic or basic conditions [20]. Since, the wastewater pH in anode chamber should be identified to enhance power generation in the MFC. Mohanakrishna et al. [21] evaluated the MFC performance with distillery wastewater by keeping at acidic environment. Ha et al. [22] adjusted the distillery wastewater at pH 7 using buffer for evaluating the performance using bacteroidetes dominant thermophilic MFC.

China became the largest car producer a decade ago, set to overtake the USA as the world’s biggest oil importer in 2017. New passenger vehicle sales in China will exceed 25 million per annum in 2017 [1]; in September 2017 alone, sales of vehicles in China reached 2,709,000 units, up 5.7% year on September 2016. Increased vehicle production and sales meet exponential growth expectations within the car industry, but the increased emissions from road transport will also have wellquantified impacts on urban air quality and greenhouse gas (GHG) emissions in China [2]. Traffic emissions have become incompatible with Chinese policies on climate change and the protection of human health. This unsustainable model results in real world emissions higher than the regulated emission factors [3], high energy usage and low utilization [4], exacerbating air quality problems in cities like Beijing. Urban air pollution has significant consequence for human health today; in 2013 premature deaths due to air pollution cost the global economy an estimated $225 billion in lost labour income, and $5.11 trillion in welfare losses worldwide, equivalent to the gross domestic product of India, Canada, and Mexico combined [5]. China alone lost ~ 10% of its GDP in 2013 as a result of air pollution according to this World Bank study. If car ownership follows the Western model, there will be 10 billion cars in China by 2100 [6]. Environmental protection and economic growth ambitions have promoted the electrification of urban transport in China, attempting to de-couple transport from urban emissions. Since the 2000s, the Chinese Government championed a national strategy for clean vehicles that is distinct from the Western model, primarily to address urban pollution [7]. At the same time, around the world, fossil fuels are increasingly seen as an investment liability, prompting significant investment shifts into decarbonised clean energy. Several national and local policies in China encouraged the development of New Energy Vehicles (NEVs) which are based on battery technologies, and other non-combustion technologies such as fuel cells (FCs), which can improve battery performance and lifetimes [8]. NEVs are essential for China to meet international climate change obligations GHG emission reduction targets, which are reviewed every 5 years under the United Nations Framework Convention on Climate Change [9]. As a result, Chinese incentives for FC vehicles (FCVs) currently extend beyond those offered for battery NEVs. This paper reviews the background to NEV policies, and the key scientific and market challenges that need to be addressed to accelerate FCs in the rapidly developing NEV market. The global significance of the Chinese market, key players, core FC technologies and future research priorities are discussed.