Use Of Hydrogen Research Articles

Technical evaluation of electrochemical separation of hydrogen from a natural gas/hydrogen mixture

In this work, we investigate the electrochemical separation of hydrogen from a 10% H2/methane natural gas blend using a single cell experimental setup for electrochemical hydrogen pumping (EHP). Results show that the overall efficiency for hydrogen separation is high, ranging from about 87% at 0.2 A/cm2 to 75% at 0.6 A/cm2. In addition, we develop a zero-dimensional model for the hydrogen separation process including the membrane permeation of H2 as well as CH4, N2, and CO2 as the main components in natural gas. We derive analytical expressions for the permeability of these gases as a function of temperature and membrane humidity using available permeability data. Although the presence of dilutive inert gases poses a challenge, the modelled data indicate that it should be possible to produce fuel cell quality hydrogen using a single hydrogen separation stage. Importantly, this indicates technological feasibility of distributing hydrogen for use in fuel cells through existing natural gas infrastructure. Extension of this research to combined hydrogen separation and compression within the same EHP unit is recommended as future work.

Microbial ecology of the deep terrestrial subsurface.

The terrestrial subsurface hosts microbial communities that, collectively, are predicted to comprise as many microbial cells as global surface soils. Although initially thought to be associated with deposited organic matter, deep subsurface microbial communities are supported by chemolithoautotrophic primary production, with hydrogen serving as an important source of electrons. Despite recent progress, relatively little is known about the deep terrestrial subsurface compared to more commonly studied environments. Understanding the composition of deep terrestrial subsurface microbial communities and the factors that influence them is of importance because of human-associated activities including long-term storage of used nuclear fuel, carbon capture, and storage of hydrogen for use as an energy vector. In addition to identifying deep subsurface microorganisms, recent research focuses on identifying the roles of microorganisms in subsurface communities, as well as elucidating myriad interactions-syntrophic, episymbiotic, and viral-that occur among community members. In recent years, entirely new groups of microorganisms (i.e. candidate phyla radiation bacteria and Diapherotrites, Parvarchaeota, Aenigmarchaeota, Nanoloarchaeota, Nanoarchaeota archaea) have been discovered in deep terrestrial subsurface environments, suggesting that much remains unknown about this biosphere. This review explores the historical context for deep terrestrial subsurface microbial ecology and highlights recent discoveries that shape current ecological understanding of this poorly explored microbial habitat. Additionally, we highlight the need for multifaceted experimental approaches to observe phenomena such as cryptic cycles, complex interactions, and episymbiosis, which may not be apparent when using single approaches in isolation, but are nonetheless critical to advancing our understanding of this deep biosphere.

Tuning hydrogen boil-off via inert gas insulation purge in a vapor cooled shielded fuel tank

Vapor cooled polymer composite tanks for liquid hydrogen are a newopportunity for light weight power-system integration into unmanned aerial vehicles. Vapor shielding has the ancillary benefit of pre-conditioning the hydrogen for use by a fuel cell. However, the mass flow rate required by a fuel cell should be matched by the natural boil-off rate of the tank. With limited ability to vary insulation thicknesses, the challenge becomes satisfying the fuel cell consumption in UAVs at different mass flow rates when at varying stages of flight from take-off, cruise, and landing. This paper provides experimental measurements of mass flow rate of hydrogen from the tank considering batch purging with helium or argon in the vapor cool shielded insulation layer. A 5-shell vapor cooled shielded tank is used with two layers of insulation including aerogel, helium or argon, and two vapor channels. A more complete understanding of system-level thermal conductance is determined by mass flow of hydrogen leaving the tank during hypothetical flight.

Hydrogen application in the fuel cycle of compressed air energy storage

The development of large energy systems based on renewable energy sources is accompanied by an increase in the input capacities of large grid storages. Taking into account the vector for decarbonization and maneuverability, the use of hydrogen as a fuel in the cycle of a diabatic compressed air energy storage (CAES) is a promising scientific and technical direction. This paper analyzes the key performance indicators of a compressed air energy storage in the presence and absence of thermal energy recovery within the cycle. In addition, an assessment was made of the prospects for the use of a methane-hydrogen mixture in gas turbines. At the end of the paper, a calculation of the process of plasma pyrolysis of methane is given as one of the possible methods for the production of hydrogen for use in energy purposes.

Techno-economic and life cycle assessment of the integration of bioenergy with carbon capture and storage in the polygeneration system (BECCS-PS) for producing green electricity and methanol

Bioenergy with carbon capture and storage (BECCS) has the potential to produce negative emissions. This study assessed the overall energy efficiency and carbon dioxide (CO2) avoidance costs and emission footprint following the integration of BECCS with a polygeneration system (BECCS-PS) for the co-production of green electricity and methanol. The process was simulated in Aspen Plus and Aspen HYSYS v.11. Oil palm empty fruit bunches were used as the feed in a biomass integrated gasification combined cycle power plant. The flue gas, which contained CO2, was captured for methanol synthesis and carbon storage. Green hydrogen for use in methanol synthesis was produced through proton exchange membrane (PEM) electrolysis powered by solar PV (PV-PEM) and geothermal power with double-flash technology (GEO-PEM). The environmental impacts of the process were investigated by a life cycle assessment and the economic aspects were evaluated using the levelized cost method. The overall system efficiency was higher in the PV-PEM scenario than in the GEO-PEM scenario. For any production capacities, the green electricity generated from the BECCS-PS plant resulted in negative emissions. A biomass power plant with a low production capacity generated higher production and CO2 avoidance costs than that with a larger production capacity. The CO2 − eq emissions and costs for methanol production in the PV-PEM scenario were larger than those in the GEO-PEM scenario, with values of -0.83 to -0.70 kg CO2 − eq/kg MeOH and 1,191–1,237 USD/ton, respectively. The corresponding values were − 1.65 to -1.52 kg CO2 − eq/kg MeOH and 918–961 USD/ton, respectively, for the GEO-PEM scenario.Graphical

Refuelling tests of a hydrogen tank for heavy-duty applications

A transition towards zero-emission fuels is required in the mobility sector in order to reach the climate goals. Here (green) renewable hydrogen for use in fuel cells will play an important role, especially for heavy duty applications such as trucks. However, there are still challenges to overcome regarding efficient storage, infrastructure integration and optimization of the refuelling process. A key aspect is to reduce the refuelling duration as much as possible, while staying below the maximum allowed temperature of 85 °C. Experimental tests for the refuelling of a 320 l type III tank were conducted at different operating conditions and the tank gas temperature measured at the front and back ends. The results indicate a strongly inhomogeneous temperature field, where measuring and verifying the actual maximum temperatures proves difficult. Furthermore, a simulation approach is provided to calculate the average tank gas temperature at the end of the refuelling process.

The operation and applicability to hydrogen fuel technology of green hydrogen production by water electrolysis using offshore wind power

Hydrogen is gaining attention as a transportation fuel due to its potential for long-term and sustainable energy supply, as well as its capacity to address security and environmental concerns. However, the widespread adoption of hydrogen fuel-cell vehicles requires overcoming certain barriers, including the vehicle-infrastructure system and zero-emission hydrogen production. Establishing a hydrogen fueling infrastructure that is compatible with hydrogen vehicles and developing sustainable hydrogen production technologies are of paramount importance. Additionally, factors such as the cost of green hydrogen production and its economic viability must be taken into account. Therefore, the development and dissemination of new technologies for carbon-free or low-carbon hydrogen production are crucial for the hydrogen production and hydrogen fuel sectors. In this study, a comprehensive model is presented for the installation of a green hydrogen production facility. The model focuses on utilizing Offshore Wind Technology (OWF) for hydrogen production through water electrolysis, as well as the storage and transportation of the produced hydrogen for use in hydrogen fuel stations. OWF technology is specifically addressed in this study to overcome its limited approach in the green hydrogen industry and address these limitations. The suggested model for green hydrogen production has been discussed, outlining the stages of hydrogen production, storage, and transportation, with its application in the Edirne-Enez location. Furthermore, a detailed techno-economic analysis of the modeled green hydrogen production facility is conducted. According to this analysis, the cost of producing green hydrogen through OWF is projected to be 6.26 EUR/kg in 2023, decreasing significantly to 1.13 EUR/kg by 2050. When accounting for fuel transportation and fuel station expenses, the overall hydrogen cost is estimated to be 10.7 EUR/kg in 2023 and 2.42 EUR/kg in 2050. Given the current state of hydrogen vehicle technology, the cost per kilometer is projected to be 0.0927 EUR/km in the year 2023 and is expected to decrease to 0.021 EUR/km by the year 2050.

Magnetic monopole's role in hydrogen bubbles formation in rapidly solidified Al–Cu–Zn alloys

Hydrogen hydrides are formed when hydrogen is trapped in the aluminum solid solution of rapidly cooled Al–Cu–Zn alloys. The formation of these hydrides is of great interest because they have unique properties that make them useful in a variety of applications. One potential application is in the field of energy storage, where hydrogen hydrides could be used as a way to store hydrogen for use in fuel cells. Another potential application is in the field of catalysis, where these materials could be used to promote chemical reactions. Highlighting of magnetic monopoles in Al-30 wt%Cu-2wt.%Zn and stable skyrmions, at room temperature, in non-magnetic Al-50 wt%Cu-2wt.%Zn is also groundbreaking development in the field of materials science, as it suggests that there may be new ways to manipulate and control the properties of these materials. We observed a remarkable consequence of these phenomena: the transmutation of aluminum into silicon. This is a significant finding, as we believe we are the first to approach this process in this way. This could lead to breakthroughs in materials science and engineering, with potential applications in fields such as electronics, photonics, and nanotechnology.

Simulation of temperature swing adsorption process to purify hydrogen for fuel cell uses by SAPO34 as adsorbent

To purify hydrogen gas from synthesis gas using a adsorption process, SAPO 34 adsorbent was used. Due to the strong adsorption of carbon dioxide in this adsorbent, it is not possible to recover the adsorbent by reducing the pressure alone, and it is necessary to use thermal operations for recovery. For this purpose, a temperature swing adsorption (TSA) process is used to increase the purity of hydrogen for use in fuel cells. To investigate the optimum operational conditions, various temperatures and different pressures of input gas were investigated to compare the purity and recovery of adsorption process. The TSA process was simulated for pressures of 11, 22 and 33 bars and the recovery percentage of each process was calculated. According to the results obtained, the recovery value at 33 bars is better than the other two pressures, but due to the fact that operational and initial costs increase at high pressures; 22 bar pressure was chosen to present the remaining results. In this work, the total amount of material and the molar rate are also reported. The average purity of the components in the product and waste outlet streams has also been presented. Accordingly, the average molar fraction of hydrogen in the product outlet stream is 99.96% in the temperature increase stage, 99.94% and in the stream used for temperature reduction is 99.96%.

Contribution to net zero emissions of integrating hydrogen production in wastewater treatment plants

The reliability of renewable hydrogen supply for off-take applications is critical to the future sustainable energy economy. Integrated water electrolysis can be deployed at distributed municipal wastewater treatment plants (WWTP), creating opportunity for reduction in carbon emissions through direct and indirect use of the electrolysis output. A novel energy shifting process where the co-produced oxygen is compressed and stored to enhance the utilisation of intermittent renewable electricity is analysed. The hydrogen produced can be used in local fuel cell electric buses to replace incumbent diesel buses for public transport. However, quantifying the extent of carbon emission reduction of this conceptual integrated system is key. In this study, the integration of hydrogen production at a case study WWTP of 26,000 EP capacity and using the hydrogen in buses was compared with two conventional systems: the base case of a WWTP with grid electricity consumption offset by solar PV and the community's independent use of diesel buses for transport, and the non-integrated configuration with hydrogen produced at the bus refuelling location operated independently of the WWTP. The system response was analysed using a Microsoft Excel simulation model with hourly time steps over a 12-month time frame. The model included a control scheme for the reliable supply of hydrogen for public transport and oxygen to the WWTP, and considered expected reductions in carbon intensity of the national grid, level of solar PV curtailment, electrolyser efficiency and size of the solar PV system. Results showed that by 2031, when Australia's national electricity is forecast to achieve a carbon intensity of less than 0.186 kg CO2-e/kWh, integrating water electrolysis at a municipal WWTP for producing hydrogen for use in local hydrogen buses produced less carbon emissions than continuing to use diesel buses and offsetting emissions by exporting renewable electricity to the grid. By 2034, an annual reduction of 390 t–CO2–e is expected after changing to the integrated configuration. Considering electrolyser efficiency improvements and curtailment of renewable electricity, the reduction increases to 872.8 t–CO2–e.

Role of hydrogen on aviation sector: A review on hydrogen storage, fuel flexibility, flame stability, and emissions reduction on gas turbines engines

Hydrogen is being recognized as a versatile energy carrier that can aid in the transition towards a decarbonized energy future due to its high specific energy density. Gas turbine engines are primary source of energy for the modern aircraft. To make the air transportation economical it is essential to achieve higher thermal efficiencies and the capability to operate on carbon–neutral fuels such as hydrogen. The current review article examines the effect of hydrogen in the gas turbine engines. Furthermore, the green routes for the hydrogen production and storage were discussed in detail. Additionally, the implementation of the conceptual design for the onboard hydrogen utilization in the long-range endurance aircrafts was considered. The utilization of hydrogen as a fuel in gas turbines is subject to the influence of different factors, including the functioning of the turbine components, ambient conditions, combustion stability, flame characteristics and operating parameters. This study explores the use of hydrogen as a fuel in aircraft gas turbine engines, which has the potential to reduce NOx emissions, improve fuel efficiency, and increase range while significantly decreasing pollutants such as carbon monoxide. However, modifications to the engine system are necessary, and careful consideration of factors such as fuel storage, combustion, and emissions is essential. While there are significant challenges to storing hydrogen for use as a fuel in aircraft, finding an optimized solution is crucial for reducing carbon emissions and moving towards a more sustainable future. Overall, hydrogen has the potential to be a viable alternative to conventional fuels in aircraft engines.

A microalgal biogas driven multigenerational system developed for producing power, freshwater and hydrogen

This research has developed a novel integrated system that uses biomass energy from microalgae and conducted in-depth thermodynamic modelling and analysis. Using all locally available potential renewable energy sources and generating the useful energy outputs to cover the community needs while minimizing the environmental damage to the ecosystem are more important than ever as the effects of global warming have got much more adverse. Regarding this particular study, the suggested multigenerational microalgae and wheat strains biomass system is developed to generate electricity, freshwater and hydrogen without any energy needs from fossil fuels, and the present system stores both electricity and hydrogen for use at a electric vehicle (EV) charging station and a hydrogen refueling station. The energy and exergy efficiencies, exergy destruction rates for individual system components, thermophysical properties and subsystem capacities are all analysed and assessed using the Engineering Equation Solver software. The results confirm that the present system produces a total of 2372.564 kW of electricity, a capacity of 2900.16 kg/day of freshwater, a capacity of 84.35 kg/day of hydrogen and a capacity of 302 kg/day of biogas by employing biomass source as a renewable energy input. Furthermore, the majority of exergy destructions occurs in the combustion chamber and the anaerobic digester. Moreover, some parametric studies are performed to investigate how varying the reference temperature (from 10 to 35 °C) influences the efficiencies and exergy destructions and how different compression ratios (such as, 9, 18, 27 and 36) affect the overall system performance in general and the Brayton cycle's exergy efficiencies in specific. The system's overall energy and exergy efficiencies are determined as 52.6% and 41.7%, respectively.

Doping Shortens the Metal/Metal Distance and Promotes OH Coverage in Non-Noble Acidic Oxygen Evolution Reaction Catalysts.

Acidic water electrolysis enables the production of hydrogen for use as a chemical and as a fuel. The acidic environment hinders water electrolysis on non-noble catalysts, a result of the sluggish kinetics associated with the adsorbate evolution mechanism, reliant as it is on four concerted proton-electron transfer steps. Enabling a faster mechanism with non-noble catalysts will help to further advance acidic water electrolysis. Here, we report evidence that doping Ba cations into a Co3O4 framework to form Co3-xBaxO4 promotes the oxide path mechanism and simultaneously improves activity in acidic electrolytes. Co3-xBaxO4 catalysts reported herein exhibit an overpotential of 278 mV at 10 mA/cm2 in 0.5 M H2SO4 electrolyte and are stable over 110 h of continuous water oxidation operation. We find that the incorporation of Ba cations shortens the Co-Co distance and promotes OH adsorption, findings we link to improved water oxidation in acidic electrolyte.

Green hydrogen production for oil refining – Finnish case

This study investigates the production of green hydrogen for use in oil refining, as specified in the draft of European union delegated act published in May 2022. The European union plans to set strict requirements of additionality and reporting regarding the criteria of renewable electricity used in hydrogen production. Alkaline electrolyzer, proton exchange membrane electrolyzer and solid oxide electrolyzer are evaluated in various scenarios supplied by wind power: power purchase agreement-based scenarios and wind power investment-based scenarios. In power purchase agreement-based scenarios baseload and pay as produced power purchase agreements (with and without electricity storage) are assessed. According to results, the use of 600 MW compressed air energy storage could reduce the dependency on the grid by 7% but increase the cost of green hydrogen significantly. Investment-based scenarios produce green hydrogen with a lower operation cost, but higher break-even price compared to power purchase agreement-based scenarios. The cheapest green hydrogen can be achieved by alkaline electrolyzer with baseload power purchase agreement. Direct ownership of wind power is outside the operation of oil refining industry, thus power purchase agreements contracting is more likely to realize.

Explicitly controlling electrical current density overpowers the kinetics of the chlorine evolution reaction and increases the hydrogen production during seawater electrolysis

The chlorine evolving reaction (CER) subdues the oxygen evolving reaction (OER) during seawater electrolysis, and impedes hydrogen production without generating harmful chlorine byproducts. We describe a new approach to suppressing CER and increasing the hydrogen production rate by highlighting its distinctive features: using electrical current densities Jc > 10 A cm−2 that are much larger than the 1 A cm−2 currents conventionally employed; and using consumable graphite rod-shaped electrodes. Our approach creates a practical means for reaching an electrochemical regime where CER is drastically reduced and hydrogen production is substantially increased. Finite element modeling indicates the rapid reduction in CER is associated with establishing a steep gradient in the electric field between the electrodes. Our study suggests that explicitly elevating Jc to more than 10 A cm−2 creates opportunities for creating hydrogen for use in large-scale and industrial applications by reducing CER to negligible levels – an environmental incentive – while increasing the OER and hydrogen production – an economic incentive.

Advanced Porous-Transport-Layer Interface Design for PEM Electrolyzers

Proton-exchange-membrane (PEM) water electrolyzers are promising technologies for generating clean hydrogen for use in a variety of sectors. The anode catalyst layer/porous-transport layer (CL/PTL) interface plays a vital role in determining performance of proton-exchange-membrane (PEM) water electrolyzers. This interface impacts ohmic, kinetic, and mass-transport overpotentials experienced by the cell. PTLs with large surface pores cause undesired catalyst layer deformation into pores of the PTL, which exacerbates degradation, and leads to high ohmic and kinetic overpotentials due to insufficient interfacial contact area.1,2 On the other extreme, low surface porosity at the interface leads to accumulation of oxygen gas that inhibit water transfer, resulting in mass-transport overpotentials.3 Thus, ideal PTLs should have hierarchical structure with high bulk porosity and low tortuosity to mitigate mass-transport overpotentials, while low surface porosity is need to enhance interfacial contact area. In this talk, we explore controlling the interfacial pore structure of these layers through a subtractive method, namely, laser ablation. Laser ablation is a facile method for tailoring the interfacial pore structure of PTLs. Heat from the laser melts titanium, granting a unique morphology advantageous to electrolyzer performance. Laser-ablated PTLs provide improved contact with the CL, while maintaining the bulk pore structure elsewhere, thereby facilitating gas removal and water transport. We also examine how laser-modified PTLs can help enable ultra-low catalyst loadings by minimizing interfacial contact resistance with the thinner catalyst layers. Overall, our work reveals that laser ablation is a facile method to enhance PEM electrolyzer performance. Acknowledgements This work was funded under the H2NEW Consortium by the Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231. References T. Schuler, R. De Bruycker, T. J. Schmidt, and F. N. Büchi, J. Electrochem. Soc., 166, F270–F281 (2019)T. Schuler, T. J. Schmidt, and F. N. Büchi, J. Electrochem. Soc., 166, F555–F565 (2019).X. Peng et al., Adv. Sci., 8 (2021).

Main-chain engineering of polymer photocatalysts with hydrophilic non-conjugated segments for visible-light-driven hydrogen evolution

Photocatalytic water splitting is attracting considerable interest because it enables the conversion of solar energy into hydrogen for use as a zero-emission fuel or chemical feedstock. Herein, we present a universal approach for inserting hydrophilic non-conjugated segments into the main-chain of conjugated polymers to produce a series of discontinuously conjugated polymer photocatalysts. Water can effectively be brought into the interior through these hydrophilic non-conjugated segments, resulting in effective water/polymer interfaces inside the bulk discontinuously conjugated polymers in both thin-film and solution. Discontinuously conjugated polymer with 10 mol% hexaethylene glycol-based hydrophilic segments achieves an apparent quantum yield of 17.82% under 460 nm monochromatic light irradiation in solution and a hydrogen evolution rate of 16.8 mmol m−2 h−1 in thin-film. Molecular dynamics simulations show a trend similar to that in experiments, corroborating that main-chain engineering increases the possibility of a water/polymer interaction. By introducing non-conjugated hydrophilic segments, the effective conjugation length is not altered, allowing discontinuously conjugated polymers to remain efficient photocatalysis.

Multi-period multi-objective optimisation model for multi-energy urban-industrial symbiosis with heat, cooling, power and hydrogen demands

Hydrogen is seen as the future energy that will help decarbonise the emissions of global energy use. Hydrogen-related technologies have recently attracted considerable attention due to their relatively low emissions and high energy yield. Even then, little attention was given to hydrogen's use in energy distribution networks. A renewable-based multi-energy system (RMES) considers power, cooling, heating, and hydrogen energy as utility systems for integrated urban and industrial areas to achieve urban-industrial symbiosis. This paper formulates the RMES as a multi-period mixed-integer nonlinear programming (MINLP) model to optimise the RMES, which minimises the financial implications and environmental impacts. Renewable solar energy is provided to the system using the photovoltaic solar system for electrical generation and the solar thermal collector for heat generation. Thermal, battery and hydrogen energy storages are integrated into the RMES to mitigate the energy supply and demand fluctuations and intermittency. A comparative analysis is conducted to individually identify the performance of different energy storage systems for economic and environmental objective functions. The comparison findings indicate that ESS performs better with 45% usage increases under objective environmental functions. The multi-objective optimisation using the ϵ-constraint method obtains the Pareto optimal solutions to the proposed multi-objective problem, which the 4th solution (ATC: 782,500 USD/y; ACE: 2,777.03 kg CO2-eq/y) appears to be the most viable. The solution maintains a high-profit level without sacrificing many opportunities for carbon emissions reduction while satisfying both objective functions simultaneously to a degree of satisfaction of 0.75. Overall, the proposed RMES is proven economical and environmentally friendly for implementation; however, the model is needed to optimise the system based on the specific situation. This study provides the optimisation model for energy recovery and technology optimisation in the multi-energy system for urban-industrial symbiosis, which minimises carbon emission and energy cost. This could lead the energy sector to achieve the Sustainable Development Goals, considering the economically and environmentally viable.

Design and tri-criteria optimization of an MCFC based energy system with hydrogen production and injection: An effort to minimize the carbon emission

The threat of rapid depletion of fossil fuel reserves and the discharge of pollutants due to the depletion of these resources has had catastrophic consequences for the ecosystem. Using efficient energy systems, waste heat recovery from these systems, and decreased carbon dioxide emission cycles is one approach to averting this looming threat in this context. It is proposed in this paper to utilize the electricity generated by the bottoming absorption power cycle to create hydrogen for use in a molten carbonate fuel cell-based energy system. The system is called near-zero carbon since the efficient waste heat utilization allows maximum hydrogen and minimum hydrocarbon fuel use. The concept of the near-zero carbon cycle is being explored from the viewpoints of technology, economics, and the environment. It is necessary to do multi-criteria optimization to establish the optimum operating point of the system under consideration to reduce costs and CO2 emissions while simultaneously increasing efficiency. A parametric analysis is performed to discover the important design parameters that impact the system's performance under consideration. Included among the factors under investigation are the fuel utilization factor (Uf), current density (J), stack temperature (Tstack), and the steam to carbon ratio (rsc). Upon investigation, it was discovered that the suggested system had an energy and exergy efficiency of around 66.21% and 59.5%, respectively. According to the findings of the exergy analysis, the MCFC and afterburner ranked highest in terms of exergy destruction (93.12 MW and 22.4 MW, respectively). The tri-objective optimization findings also reveal that the most optimal solution point has an exergy efficiency of 59.5%, a total cost rate of 11.7 ($/GJ), and CO2 emission of 0.58 ton/MWh.

Harnessing photosynthesis to produce electricity using cyanobacteria, green algae, seaweeds and plants.

The conversion of solar energy into electrical current by photosynthetic organisms has the potential to produce clean energy. Life on earth depends on photosynthesis, the major mechanism for biological conversion of light energy into chemical energy. Indeed, billions of years of evolution and adaptation to extreme environmental habitats have resulted in highly efficient light-harvesting and photochemical systems in the photosynthetic organisms that can be found in almost every ecological habitat of our world. In harnessing photosynthesis to produce green energy, the native photosynthetic system is interfaced with electrodes and electron mediators to yield bio-photoelectrochemical cells (BPECs) that transform light energy into electrical power. BPECs utilizing plants, seaweeds, unicellular photosynthetic microorganisms, thylakoid membranes or purified complexes, have been studied in attempts to construct efficient and non-polluting BPECs to produce electricity or hydrogen for use as green energy. The high efficiency of photosynthetic light-harvesting and energy production in the mostly unpolluting processes that make use of water and CO2 and produce oxygen beckons us to develop this approach. On the other hand, the need to use physiological conditions, the sensitivity to photoinhibition as well as other abiotic stresses, and the requirement to extract electrons from the system are challenging. In this review, we describe the principles and methods of the different kinds of BPECs that use natural photosynthesis, with an emphasis on BPECs containing living oxygenic photosynthetic organisms. We start with a brief summary of BPECs that use purified photosynthetic complexes. This strategy has produced high-efficiency BPECs. However, the lifetimes of operation of these BPECs are limited, and the preparation is laborious and expensive. We then describe the use of thylakoid membranes in BPECs which requires less effort and usually produces high currents but still suffers from the lack of ability to self-repair damage caused by photoinhibition. This obstacle of the utilization of photosynthetic systems can be significantly reduced by using intact living organisms in the BPEC. We thus describe here progress in developing BPECs that make use of cyanobacteria, green algae, seaweeds and higher plants. Finally, we discuss the future challenges of producing high and longtime operating BPECs for practical use.