Production & Supply Chain
A Critical Review on the Principles, Applications, and Challenges of Waste-to-hydrogen Technologies
Sep 2020
Publication
Hydrogen sourced from energy recovery processes and conversion of waste materials is a method of providing both a clean fuel and a sustainable waste management alternative to landfill and incineration. The question is whether waste-to–hydrogen can become part of the zero-carbon future energy mix and serve as one of the cleaner hydrogen sources which is economically viable and environmentally friendly. This work critically assessed the potential of waste as a source of hydrogen production via various thermochemical (gasification and pyrolysis) and biochemical (fermentation and photolysis) processes. Research has shown hydrogen production yields of 33.6 mol/kg and hydrogen concentrations of 82% from mixed waste feedstock gasification. Biochemical methods such as fermentation can produce hydrogen up to 418.6 mL/g. Factors including feedstock quality process requirements and technology availability were reviewed to guide technology selection and system design. Current technology status and bottlenecks were discussed to shape future development priorities. These bottlenecks include expensive production and operation processes heterogeneous feedstock low process efficiencies inadequate management and logistics and lack of policy support. Improvements to hydrogen yields and production rates are related to feedstock processing and advanced energy efficiency processes such as torrefaction of feedstock which has shown thermal efficiency of gasification up to 4 MJ/kg. This will affect the economic feasibility and concerns around required improvements to bring the costs down to allow waste to viewed as a serious competitor for hydrogen production. Recommendations were also made for financially competitive waste-to-hydrogen development to be part of a combined solution for future energy needs.
Electrocatalytic Properties for the Hydrogen Evolution of the Electrodeposited Ni–Mo/WC Composites
May 2021
Publication
The catalytical activity for the hydrogen evolution reaction (HER) of the electrodeposited Ni–Mo/WC composites is examined in 1 M KOH solution. The structure surface morphology and surface composition is investigated using the scanning electron microscopy X-ray diffraction and X-ray photoelectron spectroscopy. The electrocatalytic properties for the HER is evaluated based on the cathodic polarization electrochemical impedance cyclic voltammetry and chronopotentiometry methods. The obtained results prove the superior catalytic activity for the HER of Ni–Mo/WC composites to Ni–Mo alloy. The catalytic activity of Ni–Mo/WC electrodes is determined by the presence of WC nanoparticles and Mo content in the metallic matrix. The best electrocatalytic properties are identified for Ni–Mo/WC composite with the highest Mo content and the most oxidized surface among the studied coatings. The impedance results reveal that the observed improvement in the catalytic activity is the consequence of high real surface area and high intrinsic catalytic activity of the composite.
The Merit and the Context of Hydrogen Production from Water and Its Effect on Global CO2 Emission
Feb 2022
Publication
For a green economy to be possible in the near future hydrogen production from water is a sought-after alternative to fossil fuels. It is however important to put things into context with respect to global CO2 emission and the role of hydrogen in curbing it. The present world annual production of hydrogen is about 70 million metric tons of which almost 50% is used to make ammonia NH3 (that is mostly used for fertilizers) and about 15% is used for other chemicals [1]. The hydrogen produced worldwide is largely made by steam CH4 reforming (SMR) which is one of the most energy-intensive processes in the chemical industry [2]. It releases based on reaction stoichiometry 5.5 kg of CO2 per 1 kg of H2 (CH4+ 2 H2O → CO2 + 4 H2). When the process itself is taken into account in addition the production [3] becomes about 9 kg of CO2 per kg of H2 and this ratio can be as high as 12 [4]. This results in the production of about one billion tons/year of CO2. The world annual CO2 emission from fossil fuels is however much larger: it is about 36 billion tons of which roughly 25% is emitted while generating electricity and heat 20% due to transport activity and 20% from other industrial processes. Because of the link between global warming and CO2 emissions there is an increasing move towards finding alternative approaches for energy vectors and their applications.
The Optimization of Hybrid Power Systems with Renewable Energy and Hydrogen Generation
Jul 2018
Publication
This paper discusses the optimization of hybrid power systems which consist of solar cells wind turbines fuel cells hydrogen electrolysis chemical hydrogen generation and batteries. Because hybrid power systems have multiple energy sources and utilize different types of storage we first developed a general hybrid power model using the Matlab/SimPowerSystemTM and then tuned model parameters based on the experimental results. This model was subsequently applied to predict the responses of four different hybrid power systems for three typical loads without conducting individual experiments. Furthermore cost and reliability indexes were defined to evaluate system performance and to derive optimal system layouts. Finally the impacts of hydrogen costs on system optimization was discussed. In the future the developed method could be applied to design customized hybrid power systems.
A Hot Syngas Purification System Integrated with Downdraft Gasification of Municipal Solid Waste
Jan 2019
Publication
Gasification of municipal solid waste (MSW) with subsequent utilization of syngas in gas engines/turbines and solid oxide fuel cells can substantially increase the power generation of waste-to-energy facilities and optimize the utilization of wastes as a sustainable energy resources. However purification of syngas to remove multiple impurities such as particulates tar HCl alkali chlorides and sulfur species is required. This study investigates the feasibility of high temperature purification of syngas from MSW gasification with the focus on catalytic tar reforming and desulfurization. Syngas produced from a downdraft fixed-bed gasifier is purified by a multi-stage system. The system comprises of a fluidized-bed catalytic tar reformer a filter for particulates and a fixed-bed reactor for dechlorination and then desulfurization with overall downward cascading of the operating temperatures throughout the system. Novel nano-structured nickel catalyst supported on alumina and regenerable Ni-Zn desulfurization sorbent loaded on honeycomb are synthesized. Complementary sampling and analysis methods are applied to quantify the impurities and determine their distribution at different stages. Experimental and thermodynamic modeling results are compared to determine the kinetic constraints in the integrated system. The hot purification system demonstrates up to 90% of tar and sulfur removal efficiency increased total syngas yield (14%) and improved cold gas efficiency (12%). The treated syngas is potentially applicable in gas engines/turbines and solid oxide fuel cells based on the dew points and concentration limits of the remaining tar compounds. Reforming of raw syngas by nickel catalyst for over 20 h on stream shows strong resistance to deactivation. Desulfurization of syngas from MSW gasification containing significantly higher proportion of carbonyl sulfide than hydrogen sulfide traces of tar and hydrogen chloride demonstrates high performance of Ni-Zn sorbents.
Development of Visible-Light-Driven Rh–TiO2-CeO2 Hybrid Photocatalysts for Hydrogen Production
Jul 2021
Publication
Visible-light-driven hydrogen production through photocatalysis has attracted enormous interest owing to its great potential to address energy and environmental issues. However photocatalysis possesses several limitations to overcome for practical applications such as low light absorption efficiency rapid charge recombination and poor stability of photocatalysts. Here the preparation of efficient noble metal–semiconductor hybrid photocatalysts for photocatalytic hydrogen production is presented. The prepared ternary Rh–TiO2–CeO2 hybrid photocatalysts exhibited excellent photocatalytic performance toward the hydrogen production reaction compared with their counterparts ascribed to the synergistic combination of Rh TiO2 and CeO2.
Is Iridium Demand a Potential Bottleneck in the Realization of Large-Scale PEM Water Electrolysis?
Jul 2021
Publication
Proton exchange membrane water electrolysis (PEMWE) is a key technology for future sustainable energy systems. Proton exchange membrane (PEM) electrolysis cells use iridium one of the scarcest elements on earth as catalyst for the oxygen evolution reaction. In the present study the expected iridium demand and potential bottlenecks in the realization of PEMWE for hydrogen production in the targeted GW a−1 scale are assessed in a model built on three pillars: (i) an in-depth analysis of iridium reserves and mine production (ii) technical prospects for the optimization of PEM water electrolyzers and (iii) PEMWE installation rates for a market ramp-up and maturation model covering 50 years. As a main result two necessary preconditions have been identified to meet the immense future iridium demand: first the dramatic reduction of iridium catalyst loading in PEM electrolysis cells and second the development of a recycling infrastructure for iridium catalysts with technical end-of-life recycling rates of at least 90%.
Goal and Scope in Life Cycle Sustainability Analysis: The Case of Hydrogen Production from Biomass
Aug 2014
Publication
The framework for life cycle sustainability analysis (LCSA) developed within the project CALCAS (Co-ordination Action for innovation in Life-Cycle Analysis for Sustainability) is introducing a truly integrated approach for sustainability studies. However it needs to be further conceptually refined and to be made operational. In particular one of the gaps still hindering the adoption of integrated analytic tools for sustainability studies is the lack of a clear link between the goal and scope definition and the modeling phase. This paper presents an approach to structure the goal and scope phase of LCSA so as to identify the relevant mechanisms to be further detailed and analyzed in the modeling phase. The approach is illustrated with an on-going study on a new technology for the production of high purity hydrogen from biomass to be used in automotive fuel cells.
Microalgal Hydrogen Production in Relation to Other Biomass‐Based Technologies—A Review
Sep 2021
Publication
Hydrogen is an environmentally friendly biofuel which if widely used could reduce atmospheric carbon dioxide emissions. The main barrier to the widespread use of hydrogen for power generation is the lack of technologically feasible and—more importantly—cost‐effective methods of production and storage. So far hydrogen has been produced using thermochemical methods (such as gasification pyrolysis or water electrolysis) and biological methods (most of which involve anaerobic digestion and photofermentation) with conventional fuels waste or dedicated crop biomass used as a feedstock. Microalgae possess very high photosynthetic efficiency can rapidly build biomass and possess other beneficial properties which is why they are considered to be one of the strongest contenders among biohydrogen production technologies. This review gives an account of present knowledge on microalgal hydrogen production and compares it with the other available biofuel production technologies.
Free Stream Behavior of Hydrogen Released from a Fluidic Oscillating Nozzle
May 2021
Publication
The H2 internal combustion engine (ICE) is a key technology for complete decarbonization of the transport sector. To match or exceed the power density of conventional combustion engines H2 direct injection (DI) is essential. Therefore new injector concepts that meet the requirements of a H2 operation have to be developed. The macroscopic free stream behavior of H2 released from an innovative fluidic oscillating nozzle is investigated and compared with that of a conventional multi-hole nozzle. This work consists of H2 flow measurements and injection tests in a constant volume chamber using the Schlieren method and is accompanied by a LES simulation. The results show that an oscillating H2 free stream has a higher penetration velocity than the individual jets of a multi-hole nozzle. This behavior can be used to inject H2 far into the combustion chamber in the vertical direction while the piston is still near bottom dead center. As soon as the oscillation of the H2 free stream starts the spray angle increases and therefore H2 is also distributed in the horizontal direction. In this phase of the injection process spray angles comparable to those of a multi-hole nozzle are achieved. This behavior has a positive effect on H2 homogenization which is desirable for the combustion process.
Hydrogen Production on Demand by Redox-mediated Electrocatalysis: A Kinetic Study
Aug 2020
Publication
Producing hydrogen from water using a redox mediator on solid electrocatalyst particles in a reactor offers several advantages over classical electrolysis in terms of safety membrane degradation purity and flexibility. Herein vanadium-mediated hydrogen evolution on a commercial and low-cost Mo2C electrocatalyst is studied through the development of a reaction kinetics model. Based on a proposed mechanistic reaction scheme we established a kinetic rate law dependent on the concentration of V2+ the state-of-charge of the vanadium electrolyte from a vanadium redox flow battery and the amount of available catalytic sites on solid Mo2C. Kinetic experiments in transient conditions reveals a first-order dependence on both the concentration of V2+ and the concentration of catalytic active sites and a power law with an exponential factor of 0.57 was measured on the molar ratio V2+/V3+ i.e. on the electrochemical driving force generated on the Mo2C particles. The kinetic rate law was validated by studying the rate of reaction in steady-state conditions using a specially developed rotating ring-disk device (RRD) methodology. The kinetic model was demonstrated to be a useful tool to predict the hydrogen production via the chemical oxidation of V2+ over Mo2C at low pH (> 1 M H2SO4). For a perspective the model was implemented in a semi-batch reactor. The simulations highlight the optimal state-of-charge (SOC) to carry out the reaction in an efficient way for a given demand in hydrogen.
Influence of Cs Promoter on Ethanol Steam-Reforming Selectivity of Pt/m-ZrO2 Catalysts at Low Temperature
Sep 2021
Publication
The decarboxylation pathway in ethanol steam reforming ultimately favors higher selectivity to hydrogen over the decarbonylation mechanism. The addition of an optimized amount of Cs to Pt/m-ZrO2 catalysts increases the basicity and promotes the decarboxylation route converting ethanol to mainly H2 CO2 and CH4 at low temperature with virtually no decarbonylation being detected. This offers the potential to feed the product stream into a conventional methane steam reformer for the production of hydrogen with higher selectivity. DRIFTS and the temperature-programmed reaction of ethanol steam reforming as well as fixed bed catalyst testing revealed that the addition of just 2.9% Cs was able to stave off decarbonylation almost completely by attenuating the metallic function. This occurs with a decrease in ethanol conversion of just 16% relative to the undoped catalyst. In comparison with our previous work with Na this amount is—on an equivalent atomic basis—just 28% of the amount of Na that is required to achieve the same effect. Thus Cs is a much more efficient promoter than Na in facilitating decarboxylation.
Site-Dependent Environmental Impacts of Industrial Hydrogen Production by Alkaline Water Electrolysis
Jun 2017
Publication
Industrial hydrogen production via alkaline water electrolysis (AEL) is a mature hydrogen production method. One argument in favor of AEL when supplied with renewable energy is its environmental superiority against conventional fossil-based hydrogen production. However today electricity from the national grid is widely utilized for industrial applications of AEL. Also the ban on asbestos membranes led to a change in performance patterns making a detailed assessment necessary. This study presents a comparative Life Cycle Assessment (LCA) using the GaBi software (version 6.115 thinkstep Leinfelden-Echterdingen Germany) revealing inventory data and environmental impacts for industrial hydrogen production by latest AELs (6 MW Zirfon membranes) in three different countries (Austria Germany and Spain) with corresponding grid mixes. The results confirm the dependence of most environmental effects from the operation phase and specifically the site-dependent electricity mix. Construction of system components and the replacement of cell stacks make a minor contribution. At present considering the three countries AEL can be operated in the most environmentally friendly fashion in Austria. Concerning the construction of AEL plants the materials nickel and polytetrafluoroethylene in particular used for cell manufacturing revealed significant contributions to the environmental burden.
AC-DC Converters for Electrolyzer Applications: State of the Art and Future Challenges
May 2020
Publication
The main objective of the article is to provide a thorough review of currently used AC-DC converters for alkaline and proton exchange membrane (PEM) electrolyzers in power grid or wind energy conversion systems. Based on the current literature this article aims at emphasizing the advantages and drawbacks of AC-DC converters mainly based on thyristor rectifier bridges and chopper-rectifiers. The analysis is mainly focused on the current issues for these converters in terms of specific energy consumption current ripple reliability efficiency and power quality. From this analysis it is shown that thyristors-based rectifiers are particularly fit for high-power applications but require the use of active and passive filters to enhance the power quality. By comparison the association combination of the chopper-rectifier can avoid the use of bulky active and passive filters since it can improve power quality. However the use of a basic chopper (i.e. buck converter) presents several disadvantages from the reliability energy efficiency voltage ratio and current ripple point of view. For this reason new emerging DC-DC converters must be employed to meet these important issues according to the availability of new power switching devices. Finally based on the authors’ experience in power conversion for PEM electrolyzers a discussion is provided regarding the future challenges that must face power electronics for green hydrogen production based on renewable energy sources.
Techno-economic Modelling of Water Electrolysers in the Range of Several MW to Provide Grid Services While Generating Hydrogen for Different Applications: A Case Study in Spain Applied to Mobility with FCEVs
Jun 2019
Publication
The use of hydrogen as energy carrier is a promising option to decarbonize both energy and transport sectors. This paper presents an advanced techno-economic model for calculation of optimal dispatch of large-scale multi MW electrolysis plants in order to obtain a more accurate evaluation of the feasibility of business cases related to the supply of this fuel for different end uses combined with grid services' provision. The model is applied to the Spanish case using different scenarios to determine the minimum demand required from the FCEV market so that electrolysis facilities featuring several MW result in profitable business cases. The results show that grid services contribute to the profitability of hydrogen production for mobility given a minimum but considerable demand from FCEV fleets.
Characterization of the Inducible and Slow-Releasing Hydrogen Sulfide and Persulfide Donor P*: Insights into Hydrogen Sulfide Signaling
Jun 2021
Publication
Hydrogen sulfide (H2S) is an important mediator of inflammatory processes. However controversial findings also exist and its underlying molecular mechanisms are largely unknown. Recently the byproducts of H2S per-/polysulfides emerged as biological mediators themselves highlighting the complex chemistry of H2S. In this study we characterized the biological effects of P* a slow-releasing H2S and persulfide donor. To differentiate between H2S and polysulfide-derived effects we decomposed P* into polysulfides. P* was further compared to the commonly used fast-releasing H2S donor sodium hydrogen sulfide (NaHS). The effects on oxidative stress and interleukin-6 (IL-6) expression were assessed in ATDC5 cells using superoxide measurement qPCR ELISA and Western blotting. The findings on IL-6 expression were corroborated in primary chondrocytes from osteoarthritis patients. In ATDC5 cells P* not only induced the expression of the antioxidant enzyme heme oxygenase-1 via per-/polysulfides but also induced activation of Akt and p38 MAPK. NaHS and P* significantly impaired menadione-induced superoxide production. P* reduced IL-6 levels in both ATDC5 cells and primary chondrocytes dependent on H2Srelease. Taken together P* provides a valuable research tool for the investigation of H2S and per-/polysulfide signalling. These data demonstrate the importance of not only H2S but also per-/polysulfides as bioactive signaling molecules with potent anti-inflammatory and in particular antioxidant properties.
Thoughts on the Prospects of Renewable Hydrogen
Oct 2020
Publication
In the last two years or so there has been increasing interest in hydrogen as an energy source in Australia and around the world. Notably this is not the first time that hydrogen has caught our collective interest. Most recently the 2000s saw a substantial investment in hydrogen research development and demonstration around the world. Prior to that the oil crises of the 1970s also stimulated significant investment in hydrogen and earlier still the literature on hydrogen was not lacking. And yet the hydrogen economy is still an idea only.<br/>So what if anything might be different this time?<br/>This is an important question that we all need to ask and for which the author can only give two potential answers. First our need to make dramatic reductions in greenhouse gas (GHG) emissions has become more pressing since these previous waves of interest. Second renewable energy is considerably more affordable now than it was before and it has consistently outperformed expectations in terms of cost reductions by even its strongest supporters.<br/>While this dramatic and ongoing reduction in the cost of renewables is very promising our need to achieve substantial GHG emission reductions is the crucial challenge. Moreover meeting this challenge needs to be achieved with as little adverse social and economic impact as possible.<br/>When considering what role hydrogen might play we should first think carefully about the massive scale and complexity of our global energy system and the typical prices of the major energy commodities. This provides insights into what opportunities hydrogen may have. Considering a temperate country with a small population like Australia we see that domestic natural gas and transport fuel markets are comparable to and even larger than the electricity market on an energy basis.
Flexible Power & Biomass-to-Methanol Plants: Design Optimization and Economic Viability of the Electrolysis Integration
Nov 2021
Publication
This paper assesses the optimal design criteria of a flexible power and biomass to methanol (PBtM) plant conceived to operate both without green hydrogen addition (baseline mode) and with hydrogen addition (enhanced mode) following an intermittent use of the electrolysis system which is turned on when the electricity price allows an economically viable hydrogen production. The assessed plant includes a gasification section syngas cleaning and compression methanol synthesis and purification and heat recovery steam cycle to be flexibly operated. A sorption-enhanced gasification technology allows to produce a tailored syngas for the downstream synthesis in both the baseline and enhanced operating conditions by controlling the in-situ CO2 separation rate. Two designs are assessed for the methanol synthesis unit with two different reactor sizes: (i) a larger reactor designed on the enhanced operation mode (enhanced reactor design – ERD) and (ii) a smaller reactor designed on the baseline operation mode (baseline reactor design – BRD). The ERD design resulted to be preferable from the techno economic perspectives resulting in 20% lower cost of the e-MeOH (30.80 vs. 37.76 €/ GJLHV) with the baseline assumptions (i.e. 80% of electrolyzer capacity factor and 2019 Denmark day-ahead market electricity price). Other important outcomes are: (i) high electrolysis capacity factor is needed to obtain competitive cost of e-MeOH and (ii) advantages of flexibly operated PBtM plants with respect to inflexible PBtM plants are significant in scenarios with high penetration of intermittent renewables leading to low average prices of electricity but also longer periods of high peak prices.
Hydrothermal Conversion of Lignin and Black Liquor for Phenolics with the Aids of Alkali and Hydrogen Donor
Jun 2019
Publication
The potentials of phenolic productions from lignin and black liquor (BL) via hydrothermal technology with the aids of alkalis and hydrogen donors were investigated by conducting batch experiments in micro-tube reactors with 300 °C sub-critical water as the solvent. The results showed that all the employed alkalis improved lignin degradation and thus phenolics production and the strong alkalis additionally manifested deoxygenation to produce more phenolics free of methoxyl group(s). Relatively hydrogen donors more visibly facilitated phenolics formation. Combination of strong alkali and hydrogen donors exhibited synergistically positive effects on producing phenolics (their total yield reaching 22 wt%) with high selectivities to phenolics among which the yields of catechol and cresols respectively peaked 16 and 3.5 wt%. BL could be hydrothermally converted into phenolics at high yields (approaching 10 wt% with the yields of catechol and cresols of about 4 and 2 wt% respectively) with the aids of its inherent alkali and hydrogen donors justifying its cascade utilization.
Heat to Hydrogen by RED—Reviewing Membranes and Salts for the RED Heat Engine Concept
Dec 2021
Publication
The Reverse electrodialysis heat engine (REDHE) combines a reverse electrodialysis stack for power generation with a thermal regeneration unit to restore the concentration difference of the salt solutions. Current approaches for converting low-temperature waste heat to electricity with REDHE have not yielded conversion efficiencies and profits that would allow for the industrialization of the technology. This review explores the concept of Heat-to-Hydrogen with REDHEs and maps crucial developments toward industrialization. We discuss current advances in membrane development that are vital for the breakthrough of the RED Heat Engine. In addition the choice of salt is a crucial factor that has not received enough attention in the field. Based on ion properties relevant for both the transport through IEMs and the feasibility for regeneration we pinpoint the most promising salts for use in REDHE which we find to be KNO3 LiNO3 LiBr and LiCl. To further validate these results and compare the system performance with different salts there is a demand for a comprehensive thermodynamic model of the REDHE that considers all its units. Guided by such a model experimental studies can be designed to utilize the most favorable process conditions (e.g. salt solutions).
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